U.S. patent application number 14/734661 was filed with the patent office on 2015-12-10 for methods and devices to decrease tissue trauma during surgery.
The applicant listed for this patent is PHYSCIENT, INC.. Invention is credited to Hugh Charles Crenshaw, Charles Anthony Pell, Jeffrey P. Williams.
Application Number | 20150351734 14/734661 |
Document ID | / |
Family ID | 44992063 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150351734 |
Kind Code |
A1 |
Crenshaw; Hugh Charles ; et
al. |
December 10, 2015 |
METHODS AND DEVICES TO DECREASE TISSUE TRAUMA DURING SURGERY
Abstract
Methods and devices are disclosed to reduce tissue trauma when a
physician retracts a patient's tissues for surgery. In one part,
methods and devices are disclosed for controlling retraction force
and pace. In another part, methods and devices are disclosed for
oscillating force when opening. In another part, methods and
devices are disclosed for detecting trauma during retraction. In
another part, methods and devices are disclosed for balancing
forces on multiple retraction elements. In another part, methods
and devices are disclosed for reducing forces in multiple
dimensions. In another part, methods and devices are disclosed for
engaging ribs. In another part, methods and devices are disclosed
to compensate for deformation of a retractor under load. In another
part, methods and devices are disclosed that combine these methods
and devices. In another part, methods and devices are disclosed for
controlling pressure inside inflatable devices used for deforming
biological tissues.
Inventors: |
Crenshaw; Hugh Charles;
(Durham, NC) ; Pell; Charles Anthony; (Durham,
NC) ; Williams; Jeffrey P.; (Hillsborough,
NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHYSCIENT, INC. |
Durham |
NC |
US |
|
|
Family ID: |
44992063 |
Appl. No.: |
14/734661 |
Filed: |
June 9, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13111577 |
May 19, 2011 |
9049989 |
|
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14734661 |
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|
12422584 |
Apr 13, 2009 |
8845527 |
|
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13111577 |
|
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61395915 |
May 19, 2010 |
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Current U.S.
Class: |
600/202 ;
606/192 |
Current CPC
Class: |
A61B 17/0218 20130101;
A61B 17/12136 20130101; A61B 17/02 20130101; A61M 25/104 20130101;
A61B 2017/00172 20130101; A61B 2562/0219 20130101; A61B 5/442
20130101; A61B 2090/065 20160201; A61B 90/03 20160201; A61B
2017/00734 20130101; A61B 2017/00314 20130101; A61B 2017/0256
20130101; A61B 17/025 20130101; A61B 2017/00544 20130101; A61B
5/7239 20130101; A61B 2090/0809 20160201; A61B 2090/064 20160201;
A61B 2017/00323 20130101; A61B 17/0293 20130101; A61B 2017/00557
20130101; A61B 2017/0262 20130101; A61B 5/0051 20130101; A61B
2017/00398 20130101; A61B 17/0206 20130101; A61B 7/00 20130101;
A61B 2017/0225 20130101; A61B 2017/00539 20130101; A61B 2017/00181
20130101; A61B 2017/00022 20130101 |
International
Class: |
A61B 17/02 20060101
A61B017/02; A61M 25/10 20060101 A61M025/10 |
Claims
1. A fluidic system for deforming a biological tissue, comprising:
an inflatable device comprising a wall configured to be pressed
against biological tissue to apply a pressure through the wall to
the biological tissue; a tube attached to the inflatable device,
the inflatable device attached at a distal end of the tube and in
fluid communication with the tube; a pump in fluid communication
with a proximal end of the tube configured to inflate the
inflatable device; and a compliance flow control device,
comprising: a pressure release device configured to decrease fluid
pressure at the proximal end of the tube; and a controller
communicatively coupled to the pressure relief device and
configured to receive signals from measuring devices associated
with the biological tissue, determine if fluid pressure at the
proximal end of the tube should be decreased based on the received
signals, and in response cause the pressure relief device to
decrease fluid pressure at the proximal end of the tube.
2. The device of claim 1, wherein the controller is further
configured to control the rate of pumping of the pump.
3. The device of claim 1, wherein the pressure-release device is
comprised of a valve that is normally closed and, on signal from
the controller, releases fluid from the fluidic system through a
path of low fluid resistance.
4. The device of claim 1, wherein the pressure release device is
configured to be inactivated after a predetermined period of
time.
5. The device of claim 4, wherein when the pressure release device
is inactivated, the controller is configured to cause the pump to
turn on and re-pressurize the fluidic system to the pressure at
which the compliance flow control device activated the pressure
release device; and the pump resumes inflating the inflatable
device.
6. The device of claim 5, wherein the pump is configured to pause
after reaching a predetermined pressure to allow stress relaxation
of the biological tissue before further inflating the inflatable
device.
7. The device of claim 1, wherein the compliance flow control
device further composes: a first pressure measuring device in fluid
communication with the proximal end of the tube a controller
configured to: receive a signal from the first pressure measuring
device; perform a plurality of measurements based on the pressure
signal over time; compare a substantially instantaneous measurement
of the pressure signal to a variance in the plurality of
measurements over an interval of time preceding the instantaneous
measurement; and detect rupture based on the comparison.
8. The device of claim 7, wherein the plurality of measurements are
comprised of a plurality of first time derivatives of the first
signal.
9. The device of claim 7, wherein the plurality of measurements are
comprised of a plurality of second time derivatives of the first
signal.
10. The device of claim 7, wherein the variance is comprised of a
root-mean-square of the plurality of measurements.
11. The device of claim 7, wherein the control system is further
configured to determine if the ratio between the variance in the
plurality of measurements and the substantially instantaneous
measurement exceed a threshold value.
12. The device of claim 1, wherein the compliance flow control
device further composes: a first flow measuring device located at
the outlet of the pump; a second flow measuring device located at
the proximal end of the tube in fluid communication with the
inflatable device; the controller being in communication with the
first flow measuring device and the second flow measuring device
and adapted to compare the flows measured by the first measuring
device and the second flow measuring device; and flow measured by
second flow measuring device being substantially greater than flow
measured by the first flow measuring device indicates rupture of
either the biological tissue or the wall of the inflatable
device.
13. The device of claim 1, wherein the compliance flow control
device further composes: a differential pressure measuring device
in fluid communication with the fluid at two different points
inside the fluidic system such that first pressure measuring point
is closer to the pump and second pressure measuring point is
further from the pump; a fluid path having fluid resistance
separating the first and second points inside the fluidic system;
and wherein the controller is further configured to receive signals
from the differential pressure measuring device.
14. The device of claim 1, wherein the compliance flow control
device further comprises: a first differential pressure measuring
device in fluid communication with the fluid at first and second
pressure measuring points inside the fluidic system such that first
pressure measuring point is closer to the pump and second pressure
measuring point is further from the pump; a first fluid path having
high fluid resistance separating the first and second points inside
the fluidic system; a second differential pressure measuring device
in fluid communication with the fluid at third and fourth pressure
measuring points inside the fluidic system such that the third
pressure measuring point is further than the second measuring point
from the pump and fourth pressure measuring point is further than
the third pressure measuring point from the pump; a second fluid
path having high fluid resistance separating the third and fourth
points inside the fluidic system; and a comparator adapted to
determine the nearly instantaneous ratio of the signals from the
two differential pressure measuring devices. wherein the controller
is further configured to receive the signal from the
comparator.
15. The device of claim 14, wherein the controller is further
configured to perform a plurality of measurements based on the
ratio of the second differential pressure signal to the first
differential pressure signal over time; and compare a substantially
instantaneous measurement of the ratio to a variance in the
plurality of measurements over an interval of time preceding the
instantaneous measurement; and detect rupture based on the
comparison.
16. The device of claim 15, wherein the plurality of measurements
are comprised of a plurality of first time derivatives of the
ratio.
17. The device of claim 15, wherein the plurality of measurements
are comprised of second time derivatives of the ratio.
18. The device of claim 15, wherein the variance is comprised of a
root-mean-square of the plurality of measurements.
19. The device of claim 15, wherein the control system is further
configured to determine if the ratio exceeds a threshold value.
20. A method of deforming a biological tissue, comprising: pump a
fluid from a proximal end of a tube to a distal end of a tube, the
distal end of the tube in fluid communication with an inflatable
device to inflate a wall of inflatable device against biological
tissue to apply a pressure through the wall to the biological
tissue; receiving signals at a controller from measuring devices
associated with the biological tissue; determining in the
controller if fluid pressure at the proximal end of a tube should
be decreased based on the received signals; if the fluid pressure
should be decreased, the controller causing the pressure relief
device to decrease fluid pressure at the proximal end of the tube.
Description
PRIORITY AND RELATED APPLICATIONS
[0001] The present application is a continuation application to
U.S. patent application Ser. No. 13/111,577, entitled "METHODS AND
DEVICES TO DECREASE TISSUE TRAUMA DURING SURGERY," filed on May 19,
2011, which claims priority to U.S. Provisional Patent Application
No. 61/395,915, entitled "METHODS AND DEVICES TO DECREASE TISSUE
TRAUMA DURING SURGERY," filed on May 19, 2010, which are
incorporated herein by reference in their entireties.
[0002] U.S. patent application Ser. No. 13/111,577 is also a
continuation-in-part application to U.S. patent application Ser.
No. 12/422,584, entitled "METHODS AND DEVICES TO DECREASE TISSUE
TRAUMA DURING SURGERY," filed on Apr. 13, 2009, which is
incorporated herein by reference in its entirety. U.S. patent
application Ser. No. 12/422,584 claims priority to: [0003] a. U.S.
patent application Ser. No. 12/422,584 claims priority to U.S.
Provisional Patent Application No. 61/123,806, entitled
"OSCILLATING LOADING TO MINIMIZE TISSUE TRAUMA DURING SURGICAL
PROCEDURES," filed on Apr. 11, 2008, which is incorporated herein
by reference in its entirety, and [0004] b. U.S. patent application
Ser. No. 12/422,584 claims priority to U.S. Provisional Patent
Application No. 61/044,154, entitled "METHODS FOR DETECTING TISSUE
TRAUMA DURING SURGICAL RETRACTION," filed on Apr. 11, 2008, which
is incorporated herein by reference in its entirety, and [0005] c.
U.S. patent application Ser. No. 12/422,584 claims priority to U.S.
Provisional Patent Application No. 61/127,575, entitled "SURGICAL
RETRACTOR ARMS FOR REDUCED TISSUE TRAUMA," filed on May 14, 2008,
which is incorporated herein by reference in its entirety, and
[0006] d. U.S. patent application Ser. No. 12/422,584 claims
priority to U.S. Provisional Patent Application No. 61/127,491,
entitled "APPARATUS AND METHODS FOR REDUCING MECHANICAL LOADING AND
TISSUE DAMAGE DURING MEDICAL PROCEDURES," filed on May 14, 2008,
which is incorporated herein by reference in its entirety, and
[0007] e. U.S. patent application Ser. No. 12/422,584 claims
priority to U.S. Provisional Patent Application No. 61/131,752,
entitled "APPARATUS AND METHODS FOR ENGAGING HARD TISSUES TO AVOID
SOFT TISSUE DAMAGE DURING MEDICAL PROCEDURES," filed on Jun. 12,
2008, which is incorporated herein by reference in its
entirety.
FIELD OF THE DISCLOSURE
[0008] The field of the disclosure relates to spreaders,
retractors, angioplasty balloons, and retraction devices used to
deform tissue during surgery or other medical procedures.
BACKGROUND
[0009] Deformation of tissues is commonly performed during surgery
or other medical procedures either to achieve surgical access or to
specifically alter the dimensions of one part of the anatomy.
Examples of deformations of tissue for surgical access include
spreading ribs during a thoracotomy, spreading a bisected sternum
during a sternotomy, and separating the vertebrae of the spine for
surgery on the intervertebral disk. Examples of deformation of
tissues to alter the dimensions of the tissue include angioplasty
to open blocked arteries, valvuloplasty to enlarge heart valves,
and distraction to adjust the position of vertebrae. Such
deformations are collectively referred to herein as
"retraction".
[0010] Spreaders, retractors, distractors, and even angioplasty
balloons (collectively called "retractors" here) can impose
significant forces on the surrounding tissues during retraction.
The resulting strain on these tissues, and on associated tissues
such as the ligaments attaching ribs to vertebrae, can be large,
leading to damage of these tissues, including the fracture of ribs
and the rupture or irreversible deformation of ligaments and other
fibrous tissues.
[0011] Retraction occurs in two different phases-deforming the
tissue (referred to herein as the first phase or retraction) and
holding the tissue at that deformation (referred to herein as the
second phase of retraction). Usually both are done with the same
instrument. For example, a rib spreader is used both to force the
ribs apart during a thoracotomy and to hold the ribs apart during
the surgical procedure. Sometimes two different instruments are
used, especially if the deformation is to be permanent. For
example, an angioplasty balloon is used to force open an
atherosclerotic plaque, and then a stent is used to hold the artery
open; or a distractor is used to separate vertebrae, and a metal
plate is used to secure the vertebrae in that position. An example
of two different instruments being used when the deformation is not
permanent is disclosed in U.S. Pat. No. 5,201,325 by McEwen
(McEwen, Auchinleck et al. 1993), therein a surgeon manually
retract an incision with a disclosed retractor blade, and an
automated mechanism is then used to hold the incision open. In the
medical literature, both phases are frequently referred to as
retraction.
[0012] Both phases of retraction traumatize tissue. Trauma from the
first phase of retraction can include the rending and tearing of
tissues--bones bend and break; muscles stretch beyond normal
limits; ligaments and other connective tissues stretch and tear; or
nerves are stretched. Trauma from the second phase of retraction
can include ischemia of the tissue due to elevated tissue pressure,
for example, under a retractor blade; blockage of nerves; and
blockage of blood vessels causing ischemia in tissues distant from
retraction.
[0013] Tissue trauma and ensuing complications resulting from
retraction can be greater than the trauma resulting from the
medical procedure that required the retraction. For example,
thoracotomies are extremely traumatic, and can result in
post-surgical pain and respiratory complications that exceed that
of the thoracic procedure, such as a lung segmentectomy.
[0014] There is, therefore, need for improved methods and devices
to perform one or both phases of retraction.
SUMMARY OF THE DETAILED DESCRIPTION
[0015] The embodiments disclosed herein provide retraction devices
adapted to retract tissue. In one embodiment, such a device
comprises at least one pair of opposed retraction members, with
each retraction member being able to operably engage the tissue to
be retracted. A drive mechanism is operably engaged with at least
one of the retraction members in each of the at least one pair of
retraction members. The drive mechanism is adapted to provide a
continuous, smooth deformation of the tissue, following, for
example, a parabolic distance/time curve during retraction.
[0016] In another embodiment, retraction devices that are adapted
to provide a constant force during retraction of tissue. The
retraction devices comprise at least one retraction member, with
the at least one retraction member being able to operably engage
the tissue to be retracted. A drive mechanism is operably engaged
with the at least one retraction member.
[0017] In another embodiment, a retraction device includes
automated control while detecting imminent fracture. In this
manner, the automated control comprises measuring the retraction
force and monitoring for transients in the force signal, such as a
negative-going spike or an increased variance in the force
signal.
[0018] In another embodiment, a retraction device includes at least
one pad in contact with the margins of an incision. The pad is
adapted to cool the tissue at and surrounding the margin of the
incision to reduce inflammation and minimize temporary ischemia of
the tissue.
[0019] In another embodiment, a retraction device includes at least
one pad in contact with the margins of an incision. The pad is
adapted to elute pharmacologically active compounds into the
tissues at the margin of the incision to achieve beneficial
outcomes, such as hemostasis or reduced inflammation.
[0020] In another embodiment, a retraction device is provided to
retract tissue. In this manner, multiple tissue engagers that
automatically self-balance force comprise at least one retraction
member, with the at least one retraction member being able to
operably engage the tissue to be retracted. A drive mechanism is
operably engaged with the at least one retraction member.
[0021] In another embodiment, a retraction device is provided to
retract tissue with forces aligned with the retraction. The
retraction device comprises at least one pair of opposed retraction
members, with each retraction member being able to operably engage
the tissue to be retracted. A drive mechanism is operably engaged
with at least one of the retraction members in each of the at least
one pair of retraction members. At least one of the retraction
members comprises an arm that can rotate around an axis
perpendicular to the drive axis connecting the two retraction
members, permitting the retraction members to align with respect to
the retraction.
[0022] In another embodiment, a retraction device is provided to
retract tissue. In this manner, the retraction member comprises a
retractor arm fitted with tissue engagers that engage hard tissues
while minimizing deformation of soft tissues.
[0023] In another embodiment, a retraction device to retract
tissues is disclosed wherein the creep of the tissues is
accommodated. The retraction device comprises at least one pair of
opposed retraction members, with each retraction member being able
to operably engage the tissue to be retracted. A servo-drive
mechanism is operably engaged with at least one of the retraction
members in each of the at least one pair of retraction members such
that the retraction members are driven apart. At least one
retraction member comprises a retractor arm fitted with a force
measuring device that measures force on the at least one retraction
member. This measured force is used to determine the deformation of
the retraction member, and the servo-drive mechanism adjusts the
separation of the retraction members to accommodate for creep of
the tissues.
[0024] In another embodiment, a fluidic system that uses an
inflatable member for deforming biological tissue is disclosed
wherein compliance flow into the inflatable member is controlled to
reduce trauma to the biological tissue. The fluidic system
comprises an inflatable device attached to a tube that conveys
fluid pressurized by a pump to inflate the inflatable device. A
compliance flow control device uses sensors to determine if
pressure in the fluidic system should be decreased. If pressure
should be decreased, then the compliance flow control device causes
a pressure release device to decrease the pressure in the fluidic
system.
[0025] In another embodiment, the above fluidic system also
controls the rate of pumping of the pump.
[0026] In another embodiment, the above fluidic system uses a valve
as the pressure release device. The valve is usually closed, and it
opens when the compliance flow control system determines that
pressure should be released from the fluidic system.
[0027] In another embodiment, the compliance flow device activates
the pressure release device for a predetermined period of time.
[0028] In another embodiment, after the compliance flow control
device inactivates the pressure release device the pump is turned
back on to re-pressurize the fluidic system to resume inflating the
inflatable device.
[0029] In another embodiment, when re-pressuring the fluidic system
to resume inflating the inflatable device, the pump pauses after
reaching a set pressure to allow stress relaxation of the
biological tissue before further inflating the inflatable
device.
[0030] In another embodiment, a fluidic system that uses an
inflatable member for deforming biological tissue is disclosed
wherein compliance flow into the inflatable member is controlled to
reduce trauma to the biological tissue. The fluidic system
comprises an inflatable device attached to a tube that conveys
fluid pressurized by a pump to inflate the inflatable device. A
compliance flow control device uses pressure measuring devices to
determine if pressure in the fluidic system should be decreased. If
pressure should be decreased, then the compliance flow control
device causes a pressure release device to decrease the pressure in
the fluidic system. In determining whether the pressure should be
decreased, the controller in the compliance flow control device
detects rupture of the biological tissue by using a plurality of
measurements based on the pressure signal over time, comparing the
signal at the present time to the signal preceding the present
time.
[0031] In another embodiment, the comparisons over time examine the
first time derivative of the signal.
[0032] In another embodiment, the comparisons over time examine the
second time derivative of the signal.
[0033] In another embodiment, the controller compares the present
value to earlier variance in the signal.
[0034] In another embodiment, the controller determines if the
ratio between the variance in the plurality of measurements and the
substantially instantaneous measurement exceed a threshold
value
[0035] In another embodiment, a fluidic system that uses an
inflatable member for deforming biological tissue is disclosed
wherein compliance flow into the inflatable member is controlled to
reduce trauma to the biological tissue. The fluidic system
comprises an inflatable device attached to a tube that conveys
fluid pressurized by a pump to inflate the inflatable device. A
compliance flow control device uses two flow measuring devices to
determine if pressure in the fluidic system should be decreased. If
pressure should be decreased, then the compliance flow control
device causes a pressure release device to decrease the pressure in
the fluidic system. In determining whether the pressure should be
decreased, the controller in the compliance flow control device
detects rupture of the biological tissue by comparing flow rates at
two different points in the fluidic system.
[0036] In another embodiment, a fluidic system that uses an
inflatable member for deforming biological tissue is disclosed
wherein compliance flow into the inflatable member is controlled to
reduce trauma to the biological tissue. The fluidic system
comprises an inflatable device attached to a tube that conveys
fluid pressurized by a pump to inflate the inflatable device. A
compliance flow control device uses a differential pressure
measuring device to determine if pressure in the fluidic system
should be decreased. If pressure should be decreased, then the
compliance flow control device causes a pressure release device to
decrease the pressure in the fluidic system.
[0037] In another embodiment, a fluidic system uses two
differential pressure measuring devices to determine if pressure in
the fluidic system should be decreased. The fluidic system compares
the pressure differences measured by the two differential pressure
measuring devices, calculating a ratio of the two differential
pressures, to determine if pressure in the fluidic system should be
decreased. If pressure should be decreased, then the compliance
flow control device causes a pressure release device to decrease
the pressure in the fluidic system.
[0038] In determining whether the pressure should be decreased, the
controller in the compliance flow control device detects rupture of
the biological tissue by using a plurality of measurements based on
the differential pressure signal over time, comparing the signal at
the present time to the signal preceding the present time.
[0039] In another embodiment, the comparisons over time examine the
first time derivative of the signal.
[0040] In another embodiment, the comparisons over time examine the
second time derivative of the signal.
[0041] In another embodiment, the controller compares the present
value to earlier variance in the signal.
[0042] In another embodiment, the controller determines if the
ratio between the variance in the plurality of measurements and the
substantially instantaneous measurement exceed a threshold
value
[0043] In another embodiment, a method of deforming a biological
tissue is disclosed, comprising a pumping a fluid into a tube to
inflate an inflatable device is attached such that the wall of the
inflatable device press against and apply a pressure to the
biological tissue. Meanwhile, receive signals at a controller from
measuring devices associated with the biological tissue and
determine in the controller if fluid pressure at the proximal end
of a tube should be decreased based on the received signals; and if
the fluid pressure should be decreased, the controller cause the
pressure relief device to decrease fluid pressure at the proximal
end of the tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIGS. 1A and 1B illustrate two tests of a biological sample
demonstrating the biomechanical phenomena of force relaxation and
creep, respectively;
[0045] FIG. 2 is a diagram of a prior art retraction device;
[0046] FIG. 3 is a diagram of one embodiment of a device for
separating anatomical elements using a spring that exerts
substantially constant force on the anatomical elements;
[0047] FIG. 4 is a diagram of another embodiment of a device for
separating anatomical elements using a spring attached to a
moveable drive block that exerts substantially constant force on
the anatomical elements;
[0048] FIG. 5 is a diagram of another embodiment of a device for
separating anatomical elements using a spring attached to a
moveable drive block that exerts substantially constant force on
the anatomical elements, wherein the device also includes an
adjustable indicator that is used to adjust the force exerted by
the spring and a mechanical stop to limit the range of motion of a
retraction element;
[0049] FIG. 6 is a diagram of another embodiment of a device for
separating anatomical elements using a pneumatic cylinder to exert
a substantially constant force, where in a pressure reservoir can
be used to keep the pressure in the pneumatic cylinder
substantially constant as the cylinder expands, and wherein a pump
can be used to keep the pressure in the reservoir nearly
constant;
[0050] FIG. 7 is a diagram of another embodiment a device for
separating anatomical elements using a motor to exert a
substantially constant force, wherein the electrical current
driving the motor is kept substantially constant to keep the force
substantially constant;
[0051] FIG. 8 is a diagram of another embodiment of a device for
separating anatomical elements using a motor to exert a
substantially constant force, wherein a force measuring device is
used to determine the force, and a feedback loop is used to control
the motor such that the force is substantially constant;
[0052] FIG. 9 is a diagram of another embodiment of a device for
separating anatomical elements using a motor to exert a
substantially constant force which includes an alternate means for
mechanical coupling of the motor;
[0053] FIG. 10 is a diagram of another embodiment of a device for
separating anatomical elements with an alternate configuration
using more than one retraction element and also using a visual
indicator of the motion of the retraction elements;
[0054] FIGS. 11A and 11B illustrate exemplary time/displacement
trajectories for retraction with oscillating loading;
[0055] FIG. 12 illustrates a prototype motorized retractor
utilizing a bi-directional lead screw and that measures force on
both retractor blades and separation of the blades;
[0056] FIG. 13 illustrates a force/time trace for a thoracotomy
performed with the prototype motorized retractor of FIG. 12;
[0057] FIGS. 14A and 14B show acceleration of force relaxation
during bouts of oscillating loading;
[0058] FIG. 15 shows a retraction for a thoracotomy in which
oscillating loading is periodically applied;
[0059] FIG. 16 shows an example of a Finochietto thoracic retractor
in the prior art;
[0060] FIG. 17 shows a thoracic retractor of the prior art with a
standard hand-cranked rack-and-pinion and a thoracic retractor in
which the hand crank is replaced with a motor;
[0061] FIG. 18 shows a thoracic retractor driven by a computer
controlled motor on a ball screw;
[0062] FIG. 19 shows a thoracic retractor driven by a hydraulic
cylinder;
[0063] FIG. 20 shows a thoracic retractor having two actuators, a
first hand-driven actuator drives apart the arms of the retractor,
and a second motorized retractor that drives oscillating
motion;
[0064] FIG. 21 illustrates a thoracic retractor having a first
hand-driven actuator that drives apart the arms of the retractor
and a second hydraulically driven pressure pad used to drive
oscillating motion;
[0065] FIG. 22 shows a thoracic retractor having a first
hand-driven actuator that drives apart the arms of the retractor
and a second voice coil actuator used to drive oscillating
motion;
[0066] FIG. 23 shows a retractor having multiple arms and actuators
that apply oscillating loads;
[0067] FIG. 24 shows a retractor having multiple pairs of arms and
actuators, wherein one actuator separates the pairs of arms, while
actuators on each arm drive oscillating motion;
[0068] FIG. 25 shows an angioplasty system for dilating tissues
with an oscillating motion;
[0069] FIG. 26 shows another angioplasty system with an oscillating
motion;
[0070] FIGS. 27A through 27C illustrates an angioplasty system with
two compartments to generate oscillating motions having higher
frequencies;
[0071] FIGS. 28A and 28B show another angioplasty system with two
compartments to generate oscillating motions having higher
frequencies;
[0072] FIGS. 29A and 29B show another angioplasty system in which
all components are contained in a single compartment to permit
oscillating motions having higher frequencies;
[0073] FIGS. 30A and 30B show another angioplasty system in which
oscillating motions are driven by a thermally expanded bubble;
[0074] FIG. 31 illustrates how the time constant can be determined
for force relaxation;
[0075] FIG. 32 illustrates how effective stiffness can be compared
for sequential cycles of an oscillating loading;
[0076] FIG. 33 depicts an example retractors in the prior art;
[0077] FIG. 34 illustrates the retractor of FIG. 33 fitted with a
set of calipers for measuring the separation of retraction elements
and with strain gauges for measuring the forces on each of the
blades of the retraction elements;
[0078] FIG. 35 shows a prototype retractor having a motorized
drive, a linear potentiometer for measuring the separation of the
retraction elements, and strain gauges for measuring the forces on
each of the blades of the retraction elements;
[0079] FIG. 36 shows force and displacement with respect to time
for a retraction during an experimental thoracotomy on a pig
carcass;
[0080] FIG. 37 shows force and displacement with respect to time
for a retraction during an experiment thoracotomy on a pig using a
Finochietto-style retractor;
[0081] FIGS. 38A through 38C shows force and displacement with
respect to time for a second retraction during another experimental
thoracotomy on a pig carcass, wherein a larger break and two
smaller breaks occurred during this retraction and two force events
and a slope event preceded the larger break;
[0082] FIG. 39 shows the force and the slope of the force in an
expanded view of the retraction in FIG. 38. This shows how
examination of the slope provides a clearer signal of the slope and
force events;
[0083] FIGS. 40A and 40B illustrate the force and the slope of the
force over time for a third retraction during another experimental
thoracotomy on a pig carcass;
[0084] FIGS. 41A and 41B illustrate the force and a second time
derivative of the force (d2F/dt2) for two experimental
retractions;
[0085] FIG. 42 shows an algorithm for detecting an imminent tissue
fracture and pausing retraction in response;
[0086] FIG. 43 shows how acoustic events during retraction can
occur over time during a retraction and how they can be used as
predictors of tissue fracture;
[0087] FIG. 44 shows an example of a Finochietto thoracic retractor
in the prior art;
[0088] FIGS. 45A and 45B show an experimental thoracic retractor in
the prior art;
[0089] FIG. 46 show the orientations and motions of a swingletree
and the forces on the swingletree;
[0090] FIG. 47 shows the orientations and motions of a doubletree
and the forces on the doubletree;
[0091] FIGS. 48A and 48B shows an example of the prior art in which
a derrick-like arm suspends a swingletree over an incision;
[0092] FIGS. 49A, 49B.1 and 49B.2 show the use of a balancing
assembly in a thoracic retractor having multiple retractor
blades;
[0093] FIG. 50A through SOC show how a balancing assembly can be
adjusted to provide any ratio of forces on multiple retractor
blades;
[0094] FIG. 51 shows a balancing assembly having multiple tiers of
balance bars;
[0095] FIG. 52 shows a balancing assembly having a number of blades
that is not a multiple of 2;
[0096] FIG. 53 shows a retractor having a cable that permits a
balance bar to rotate;
[0097] FIG. 54 shows a balancing assembly having multiple tiers,
with each tier free to rotate;
[0098] FIGS. 55A through 55C show top, side, and front views,
respectively, of a balance assembly used for retracting a rib,
wherein hooks that descend from the balance bars engage the
rib;
[0099] FIGS. 56A through 56C shows top, side, and front views,
respectively, of a balance assembly used for retracting a rib,
wherein hooks that descend from the balance bars engage the rib and
an articulation in the balance bar permits the hooks to orient to
the curvature of the rib;
[0100] FIG. 57 shows a thoracic retractor with a balancing
assembly, wherein the arms of the retractor has articulations;
[0101] FIG. 58 shows a balancing assembly in which balance bars
overlap;
[0102] FIGS. 59A through 59E shows another embodiment of a
retractor having articulations in the arms, retraction hooks to
engage the tissues, and cables to provide automatic force balancing
on the hooks;
[0103] FIGS. 60A and 60B show the embodiment depicted in FIGS. 59A
through 59E, but as part of a retractor driven on a dual-thrust
lead screw;
[0104] FIG. 61 shows another embodiment of a retractor using
hydraulic cylinders to provide automatic force balancing on
multiple retractor blades;
[0105] FIG. 62 shows another embodiment in which hydraulic
cylinders provide automatic force balancing for multiple retraction
hooks;
[0106] FIGS. 63A through 63E show another embodiment in which
fenestrated bars on a fulcrum provide automatic force balancing for
multiple retraction hooks;
[0107] FIG. 64 show another embodiment in which pivots are used to
provide adjustable pivot points for swingletrees;
[0108] FIG. 65A through 65C show side views of the assembly in FIG.
64.
[0109] FIGS. 66A and 66B show another embodiment in which pivots
are used to provide adjustable pivot points for swingletrees;
[0110] FIG. 67 shows an example of a thoracic retractor in the
prior art used in a thoracotomy;
[0111] FIGS. 68A and 68B show examples of retractors in the prior
art;
[0112] FIG. 69 diagrams the forces thought to act on the opposing
blades of a retractor;
[0113] FIGS. 70A through 70D show additional examples of the prior
art in which curved blades or swiveling joints permit accommodation
to forces of retraction;
[0114] FIG. 71 shows a more complete accounting of the forces and
torques on a retractor;
[0115] FIG. 72 shows data from an experimental thoracotomy showing
that the force is not equal on two opposing blades of a
retractor;
[0116] FIG. 73 shows an embodiment in which the retraction units
are driven by a dual-thrust lead screw;
[0117] FIG. 74 shows another embodiment in which the retraction
units are driven by a dual-thrust lead screw, demonstrating
rotational freedom of the arms;
[0118] FIG. 75 shows side and end views, respectively, of an
embodiment of a retractor drive mechanism comprising a roller drive
with a shaft having rectangular cross-section;
[0119] FIG. 76 shows how torques on the arms of a retractor
increases forces on the drive rollers of a roller drive;
[0120] FIG. 77 shows a roller drive with a circular shaft and how
alignment of the rollers with respect to the circular shaft drives
rotation and translation of the shaft;
[0121] FIG. 78 illustrates multiple views of a roller drive with a
circular shaft depicting how varying the alignment of the rollers
with respect to the circular shaft provides variable control of
shaft rotation and translation;
[0122] FIG. 79 shows another embodiment of a retractor using a
roller drive with a circular shaft;
[0123] FIG. 80 shows a another n embodiment of a retractor having
dovetail joints to permit additional motions of the retractor
arms;
[0124] FIG. 81 shows another embodiment of a retractor arm having
two dovetail joints to permit additional motions of the retractor
arms;
[0125] FIGS. 82A and 82B shows another embodiment of a retractor
having two dual-thrust lead screws permitting an additional degree
of freedom of motion;
[0126] FIG. 83 shows another embodiment of a retractor for
thoracotomy comprising retractor blades pulled by straps attached
to a patient;
[0127] FIG. 84 shows another embodiment of a retractor for
sternotomy comprising retractor blades pulled by two ends of a
strap that wraps around a patient;
[0128] FIG. 85 shows another embodiment of a retractor for
sternotomy comprising retractor blades pulled by the two ends of a
strap that wraps around a patient and inflatable balloons for
generating tension;
[0129] FIG. 86 shows an example of a Weitland retractor in the
prior art for retracting skin inserted into an incision in the
skin;
[0130] FIG. 87 shows another embodiment of a retractor comprising
retractor blades pulled by straps that wrap around the patient's
wrist and having pull tabs for generating retraction forces;
[0131] FIGS. 88A and 88B shows the anatomy of a chest wall around
an incision for a thoracotomy;
[0132] FIG. 89 shows the deformation of the tissues of the chest
wall by retractor blades during a thoracotomy;
[0133] FIG. 90 shows pinch points generated by retractor blades on
the ribs and neurovascular bundle during a thoracotomy;
[0134] FIG. 91 shows regions of potential damage to tissues caused
by elevated tissue pressure during thoracotomy;
[0135] FIGS. 92A through 92C show an embodiment of a tissue
engaging element comprising posts placed into holes drilled into
adjacent ribs;
[0136] FIG. 93 shows another embodiment of a retractor comprising
posts that engage the arms of the retractor;
[0137] FIGS. 94A and 94B show another embodiment of a retractor
comprising clips that grasp the ribs and attach to the arms of a
retractor;
[0138] FIGS. 95A and 95B show embodiments of retractor clips having
one or two spikes, respectively, for engaging the ribs;
[0139] FIG. 96 shows a top view of another embodiment of a
retractor comprising two retractor arms and multiple clips for
engaging the ribs for a thoracotomy;
[0140] FIGS. 97A through 97D show the top and side views of another
embodiment of a retractor comprising two retractor arms having
descender posts for engaging ribs, and two side views of a
descender posts having hooks and rotatable mounts;
[0141] FIGS. 98A and 98B show another embodiment of a descender
post comprising a hook engaged with the retractor arm via a
rotatable mount;
[0142] FIG. 99 shows a 3D model of a retractor having descender
posts with hooks rotatably mounted on retractor arms;
[0143] FIG. 100 shows another embodiment of a retractor arm
comprising an arm and a plurality of descender posts for engaging a
rib;
[0144] FIGS. 101A through 101E shows another embodiment of a
descender post comprising a projection that projects laterally from
the descender post and terminates in a tip having one of several
configurations;
[0145] FIG. 102 shows another embodiment of a retractor comprising
two retractor arms each having a first and a second descender post
for engaging a rib;
[0146] FIG. 103 shows another embodiment of a retractor comprising
multiple arms, each having descender posts and configured to engage
multiple ribs on each side of a thoracotomy incision;
[0147] FIGS. 104A through 104C shows another embodiment of a
descender post comprising a post with clips on one end, wherein the
clips close on a rib when pushed against the rib;
[0148] FIGS. 105A and 105B show the deformations under loading of a
thoracic retractor in the prior art;
[0149] FIG. 106 shows an embodiment comprising a retractor having
two opposing blades, a servo-motor, a servo-controller, and linear
potentiometer;
[0150] FIG. 107 shows an algorithm in which force on the retractor
is used to determine and correct for deformation of the retractor
when loaded;
[0151] FIG. 108 shows an embodiment of a device for compensating
for changes in retractor deformation comprising a force measuring
device, a force-to-deformation translator, a servo-controller and a
servo-motor;
[0152] FIG. 109 shows an embodiment of a device for compensating
for changes in retractor deformation comprising a force measuring
device, a force-to-deformation translator, a servo-controller and a
servo-motor in which all components fit onto one arm of the
retractor;
[0153] FIG. 110 shows an embodiment of a thoracic retractor;
[0154] FIG. 111 shows an embodiment of a retraction driver;
[0155] FIG. 112 shows an embodiment of a retractor arm assembly for
a thoracotomy;
[0156] FIG. 113 shows an enlarged view of a rotatable mount on a
thoracic retractor;
[0157] FIG. 114 shows the design of the balance arms of a retractor
arm assembly;
[0158] FIG. 115 shows an example of a user interface built into a
thoracic retractor;
[0159] FIGS. 116A and 116B show force and displacement for two
automated thoracotomy retractions performed with a prototype
thoracic retractor; and
[0160] FIGS. 117A through 117C show the force on a left arm and an
Event Detection Signal for the automated retractions shown in FIGS.
116A and 116B.
[0161] FIGS. 118A through 118C show and example of the prior art in
which an angioplasty balloon is expanded to dilate a blood
vessel.
[0162] FIG. 119 shows a device made of non-compliant materials to
reduce compliance flow in a system for dilating a biological
tissue.
[0163] FIG. 120 shows a device made of non-compliant materials that
includes a pressure gauge to reduce compliance flow in a system for
dilating a biological tissue.
[0164] FIG. 121 shows a system for dilating a biological tissue
with a mechanism that includes a switching valve for adding
additional fluid to a system for dilating a biological tissue.
[0165] FIG. 122 shows the system in FIG. 121 but with the switching
valve in the position for adding fluid.
[0166] FIG. 123 shows a catheter with sheath enclosing multiple
smaller tubes.
[0167] FIG. 124 shows a catheter with sheath enclosing multiple
smaller tubes and wires.
[0168] FIG. 125 shows a means for sealing the end of a catheter
having a sheath with multiple smaller tubes and wires.
[0169] FIG. 126 shows a device for attaching multiple pumps to
multiple smaller tubes and wires to an electrical board.
[0170] FIG. 127 shows a device having multiple small tubes and
wires enclosed in a common sheathing that connect with an
angioplasty balloon and a pressure gauge attached to the wire
inside the lumen of the balloon.
[0171] FIG. 128 shows an angioplasty balloon and catheter with
multiple tubes and wire enclosed in a common sheathing and with one
tube in fluid communication with the lumen of the vessel, one tube
in fluid communication with the lumen of the balloon, and the wire
connected to a pressure gauge.
[0172] FIG. 129 shows a non-compliant fluidic system for inflating
an angioplasty balloon with precisely controlled pressure and
volume of inflation while also delivering a second fluid downstream
of the angioplasty balloon.
[0173] FIG. 130 shows pressure and the slope of pressure varying
over time when a component of a plaque fails.
[0174] FIG. 131 shows pressure and its second time derivative
varying over time when a component of a plaque fails.
[0175] FIG. 132 shows an algorithm for detecting imminent tissue
trauma in a plaque or blood vessel wall.
[0176] FIG. 133 shows a non-compliant fluidic system with a
pressure gauge measuring pressure inside a small tube.
[0177] FIG. 134 shows a 6-port switching valve used to inject a
fluid into the stream of fluid from a syringe pump.
[0178] FIG. 135 shows a catheter with sheath enclosing multiple
smaller tubes, wires, and fiber optics.
[0179] FIG. 136 shows another embodiment for controlling flow into
an angioplasty balloon.
[0180] FIG. 137 shows an alternate means by which resistance to
flow in a tube can be achieved by using a small internal diameter
over only the distal region of the tube.
[0181] FIG. 138 shows a fluidic system in which a second pump can
be placed in fluid communication with the proximal end of a tube to
reduce pressure in the fluidic system.
[0182] FIG. 139 shows a fluidic system that uses a pressure
measuring device to detect failure of a biological tissue and then
control compliance flow.
[0183] FIG. 140 shows a fluidic system that uses flow measuring
devices to detect failure of a biological tissue and then control
compliance flow.
[0184] FIG. 141 shows a fluidic system that uses a single flow
measuring device to detect failure of a biological tissue and then
control compliance flow.
[0185] FIG. 142 shows a fluidic system that uses two flow measuring
devices to detect failure of a biological tissue and then control
compliance flow.
[0186] FIG. 143 shows a fluidic system that uses two pressure
measuring devices to detect failure of a biological tissue and then
control compliance flow.
[0187] FIG. 144 shows a fluidic system that uses a different
configuration of two pressure measuring devices to detect failure
of a biological tissue and then control compliance flow.
[0188] FIG. 145 shows a fluidic system that uses two pressure
measuring devices and a compliant fluidic component to detect
failure of a biological tissue and then control compliance
flow.
[0189] FIG. 146 shows a flow measuring device comprising a
differential pressure measuring device and a fluidic channel of
known resistance to flow.
[0190] FIG. 147 shows a fluidic system that uses a differential
pressure measuring device to detect failure of a biological tissue
and then control compliance flow.
[0191] FIG. 148 shows a fluidic system that uses two differential
pressure measuring devices to detect failure of a biological tissue
and then control compliance flow.
DETAILED DESCRIPTION
[0192] A. Constant Force (creep)
[0193] Many biological materials are viscoelastic, so they exhibit
time-dependent mechanical properties (Wainwright et al., 1976,
Mechanical Design in Organisms, John Wiley & Sons; Woo et al.,
1999, Animal Models in Orthopaedic Research, CRC Press. pp. 175-96;
Provenzano et al., 2001, Ann. Biomed. Eng. 29:908; Vanderby and
Provenzano, 2003, J. Biomech. 10:1523; Yin and Elliott, 2004, J.
Biomech. 37:907). To simplify this discussion, consider the force
(the stress) required to stretch a sample of biological material.
Consider FIG. 1A which illustrates test on a sample A200 of a
biological material whereby the sample A200 is stretched by an
instrument has a stationary unit A202 that measures force and a
moving unit A204 that measures displacement while stretching a
sample. The sample A200 is initially stretched by having the moving
unit A204 move away from the stationary unit A204. The stationary
unit A204 then remains at a fixed position, holding the sample A200
at constant deformation. Over time, the measured force decreases.
This is an example of "force relaxation" or "stress relaxation".
FIG. 1B shows a similar test on sample A200. Initially, the sample
A200 is stretched; however, now moving unit A204 moves such that a
constant force is applied to sample A200, and now the sample A200
stretches longer over time, a phenomenon known as "creep". Force
relaxation and creep occur when retracting an incision. The
deformations of the tissues around the incision are more complex
than the simple stretch shown in FIGS. 1A and 1B, but the tissues,
nevertheless, exhibit force relaxation and creep.
[0194] Standard practice during a sternotomy or thoracotomy is to
spread the ribs slowly to a few centimeters, hold for a minute or
so (allowing stress relaxation), and then slowly open over several
minutes (allowing continued viscous deformation/stress relaxation)
to the final opening.
[0195] The time dependent behavior of biological tissues has been
specifically considered in the design of some retraction devices.
U.S. Pat. No. 4,899,761 to Brown and Holmes discloses a distractor
for separating vertebrae to measure spinal instability. The
distractor of Brown and Holmes uses constant velocity deformation
to standardize measurements of the mechanical properties of the
motion segment of a spine to diagnose whether surgical intervention
is necessary. Additionally, US Patent Application Publication No.
2006/0025656 to Buckner and Bolotin discloses stress relaxation as
a means of reducing force during retraction.
[0196] Creep has not been considered in the design of retraction
devices. However, application of a constant force ensures that (a)
an unexpectedly or inappropriately large force is applied as would
be the case for manual or motor driven retraction devices, and (b)
viscoelastic deformation is allowed to proceed, thereby reducing
the loads on anatomical elements that might rupture.
[0197] Different embodiments are disclosed, with reference to the
figures, of assemblies and devices that apply a substantially
constant force to one or more anatomical elements to move the
anatomical elements. Not all embodiments of the invention are
shown. Indeed, these inventions may be embodied in many different
forms and should not be construed as limited to the embodiments set
forth herein; rather, these embodiments are provided so that this
disclosure satisfies applicable legal requirements.
[0198] FIG. 2 illustrates a retraction device in the prior art.
Retractor A2 is a mechanical device utilizing two opposed
retraction elements A6, AS. Each retraction element A6, AS has a
blade A4 that is inserted into an incision, each blade A4 engaging
one side of an incision. One retraction element AS is moveable with
respect to the other retraction element A6, with motion being
driven by a rack-and-pinion drive AI0 that is manually driven with
a drive handle A12. The retraction elements A6, AS exert a force on
the anatomical elements on either side of the incision to separate
the anatomical elements, thereby opening the incision. A limitation
of this device is that the force can vary dramatically with small
displacements, thus an operator might exert an inappropriate force
while attempting to move the retraction elements A6, AS only a
small distance.
[0199] FIG. 3 illustrates an embodiment of the present invention
which is designed to apply a constant force. It is a mechanical
device utilizing two opposed retraction elements A16 and AIS. Each
retraction element A16, AIS has a blade A14 (similar to blade A4)
that is inserted into an incision, each blade A14 engaging one side
of the incision. One retraction element A16 is moveable with
respect to the other retraction element AIS and is mounted on a
sliding carriage A20. The sliding carriage A20 is driven by a
spring A26 that exerts a substantially constant force over the
range of motion such that the force exerted by the opposing
retraction elements A16, A18 on the anatomical elements is
substantially constant. The spring A26 is connected to a moveable
anchor block A22 that allows an operator to adjust the stretch of
the spring A26 and, thereby, the force exerted by the spring A26 on
the anatomical element via the sliding carriage A20. The moveable
anchor block A22 has a lock screw A24 to secure the position of
moveable anchor block A22 after adjustment. Thus, the spring A26
serves to exert a substantially constant force, and this force
cannot be accidentally exceeded by, for example, attempting to move
the retraction elements A16 and A18 a small distance. Furthermore,
if the spring A26 does not have a large spring constant, then the
distance from the sliding carriage A20 to the moveable anchor block
A22 can be sufficiently large that small errors in adjustment of
this distance do not introduce large errors in the force.
[0200] FIG. 4 illustrates another embodiment of the present
invention which is designed to apply a substantially constant force
that is larger than that depicted in FIG. 3. It is a mechanical
device utilizing two opposed retraction elements A30, A32. Each
retraction element A30, A32 has a blade A28 (similar to blade A4)
that is inserted into an incision, each blade A28 engaging one side
of the incision. One retraction element A30 is moveable with
respect to the other A32, being mounted on a sliding carriage A34.
The sliding carriage A34 is driven by a spring A39 that exerts a
substantially constant force over the range of motion such that the
force exerted by the opposing retraction elements A30 and A32 on
the anatomical elements is substantially constant. The spring A39
is connected to a driven anchor block A36 that allows an operator
to adjust the stretch of the spring A39 and, thereby, the force
exerted by the spring A39 on the anatomical element via the sliding
carriage A34. The driven anchor block A36 has a manual drive
mechanism, such as a ratchet or a rack-and-pinion, driven by a
handle A38 for manual drive and, optionally, a lock screw to secure
the position of the driven anchor block A36 after adjustment.
[0201] FIG. 5 illustrates another embodiment of the present
invention that provides an indicator of the force exerted on the
tissue. It is a mechanical device utilizing two opposed retraction
elements A42, A44. Each retraction element A42, A44 has a blade A40
(similar to blade A4) that is inserted into an incision, each blade
A40 engaging one side of the incision. One retraction element A42
is moveable with respect to the other retraction element A44, and
is mounted on a sliding carriage A46. The sliding carriage A46 is
driven by a spring A54 that exerts a substantially constant force
over the range of motion such that the force exerted by the
opposing retraction elements A42, A44 on the anatomical elements is
substantially constant. The spring A54 is connected to a driven
anchor block A48 that allows an operator to adjust the stretch of
the spring A54 and, thereby, the force exerted by the spring A54 on
the anatomical element via the sliding carriage A46. The driven
anchor block A48 has a manual drive mechanism, such as a ratchet or
a rack-and-pinion drive, driven by a handle A50 for manual drive
and, optionally, a lock screw to secure the position of the driven
anchor block A48 after adjustment. There is also a force indicator
A60 that is a graduated rod, with graduations indicating force
exerted by the spring A54 for the indicated stretch, that is used
to indicate where to place the driven anchor block A48 or whether
the driven anchor block A48 should be moved to maintain appropriate
stretch of the spring A54 to maintain a substantially constant
force on the moveable retraction element A42. The position of the
force indicator A60 is secured by an indicator set screw A52. There
is also a mechanical stop A56 with its position secured by the stop
set screw AS 8 such that the motion of the sliding carriage A46
cannot exceed a predetermined motion.
[0202] FIG. 6 illustrates another embodiment of the present
invention that uses a pneumatic piston to exert a substantially
constant force. It is a mechanical device utilizing two opposed
retraction elements A64, A66. Each retraction element A64, A66 has
a blade A62 (similar to blade A4) that is inserted into an
incision, each blade A62 engaging one side of the incision. One
retraction element A64 is moveable with respect to the other
retraction element A66, and is mounted on a sliding caiTiage A68.
The sliding carriage A68 is driven by a pneumatic piston A74 that
exerts a substantially constant force over the range of motion such
that the force exerted by the opposing retraction elements A64, A66
on the anatomical elements is substantially constant. The piston
A74 is connected to a pressure reservoir A80 by a pressure hose
A76. The pressure reservoir A80 has sufficient volume of gas such
that changes in the volume of the piston A74 as the piston A74
moves do not introduce large changes in the pressure. The pressure
reservoir A80 can be fitted with a pressure gage A78 that allows an
operator to observe the pressure. The pressure reservoir A80 can be
connected to a pressure pump A86 that permits an operator to
increase the pressure in the reservoir both to initiate the force
at the piston A74 or to prevent pressure from dropping in the
pressure reservoir A80 should the motion of the piston A74 be too
large, causing a drop in pressure, or to allow the piston A74 to
change from a first substantially constant force to a second
substantially constant force. The pressure reservoir A80 also can
have a bleed valve A82 that allows an operator to reduce the
pressure, to release the pressure, or to move from a first
substantially constant force to a second substantially constant
force. Additionally, there can be a mechanical stop A70 with its
position secured by a stop set screw A72 such that the motion of
the sliding carriage A68 cannot exceed a predetermined motion.
[0203] FIG. 7 illustrates another embodiment of the present
invention which utilizes a motorized drive to exert a substantially
constant force. It is a mechanical device utilizing two opposed
retraction elements A90, A92. Each retraction element A90, A92 has
a blade A88 (similar to blade A4) that is inserted into an
incision, each blade A88 engaging one side of the incision. One
retraction element A90 is moveable with respect to the other
retraction element A92, and is mounted on a sliding carriage A94.
The sliding carriage A94 is driven by a motor A96 that exerts a
substantially constant force over the range of motion such that the
force exerted by the opposing retraction elements A90, A92 on the
anatomical elements is substantially constant. The motor A96 is
connected by an electrical cable A98 to a motor controller (not
shown). The motor controller ensures that the torque generated by
the motor A96 is substantially constant such that the force exerted
by the opposing retraction elements A90, A92 on the anatomical
elements is substantially constant.
[0204] FIG. 8 illustrates another embodiment of the present
invention which utilizes a feedback system to exert a substantially
constant force. It is a mechanical device utilizing two opposed
retraction elements A102, A104. Each retraction element AIO2, A104
has a blade A1OO (similar to blade A4) that is inserted into an
incision, each blade AIOO engaging one side of the incision. One
retraction element A102 is moveable with respect to the other A104
and is mounted on a sliding carriage A106. The sliding carriage
A106 is driven by a motor A1ii that exerts a substantially constant
force over the range of motion such that the force exerted by the
opposing retraction elements A102, A104 on the anatomical elements
is substantially constant. The motor A Ill is connected by an
electrical cable A108 to a motor controller A114. A force measuring
device A110 is attached to the retraction element AI04 (or
optionally to retraction element AI 02) such that the force
measuring device A110 determines the force exerted by the
retraction element A104 on the anatomical element. The force
measuring device AIIO is connected to the motor controller A114 via
a signal cable A112 such that the force is transmitted as a signal
to the motor controller A114. The motor controller A114 implements
a feedback loop such that the force measured by the force measuring
device A110 is substantially constant such that the force exerted
by the opposing retraction elements AI02, AI04 on the anatomical
elements is substantially constant. Motor controller A114 can,
optionally, be connected to another device (not shown) by cable
A116 to, for example, provide additional processing abilities or to
provide a display of force.
[0205] FIG. 9 illustrates another embodiment of the present
invention that is similar to that disclosed in FIG. 7 but in which
a motor A124 is mounted differently. Motor A124 is directly
attached to retractor element A120 by mount A126, and retractor
element A122 is directly attached to the linear drive shaft A127.
This permits use of a differently configured motor, possibly with
integrated motor controller (not shown) or connected by a cable
A128.
[0206] FIG. 10 illustrates another embodiment of the present
invention which is a mechanical device utilizing multiple moveable
retraction elements A132, A134 that are mounted on a frame A130.
Each moveable retraction element A132, A134 can be independently
moved. The various mechanisms described in FIGS. 3 through 9 for
exerting a substantially constant force via the blades A138
(examples of blades include curved or bent blades that extend into
the incision) of retraction elements can be implemented for each of
these moveable retraction elements A132, A134. The mechanisms can
be implemented such that the force exerted by each individual
moveable retraction element A132, A134 is independent of the force
exerted by any other moveable retraction element A132, A134.
Optionally, position measuring devices (not shown, examples include
linear potentiometers, LVDTs, optical encoders) can be placed on
each moveable retraction element A132 and A134 such that an
independent measure of position is determined and displayed on a
visual position indicator A136 on the frame A130. Alternatively,
the force exerted by blades A138 of retraction elements A132, A134
on their respective anatomical elements can be measured by a force
measuring device (not shown, examples include appropriately placed
strain gauges), and the forces displayed on indicators (not shown)
also on the frame A130. An electrical cable A137 can be used to
provide power to electrical devices on the frame A130 and to convey
electrical signals from electrical devices on the frame A130 or
elsewhere on the retractor to a separate motor controller (not
shown) or computer (not shown).
B. Oscillating Loading
[0207] Deformation of biological materials during the first phase
of retraction is usually done one-directionally--the deformation
pushes anatomical elements apart (e.g., thoracotomy) or stretches
arteries open (e.g., angioplasty). The direction of motion during
deformation is rarely reversed and then only to correct for errors,
such as to reposition a rib retractor that has slipped or to free a
blood vessel that has accidentally been captured under a retractor
blade.
[0208] Trauma to the displaced tissue is a common consequence of
these deformations. Ribs fracture during thoracotomy, costosternal
joints dislocate during sternotomy, muscles tear during retraction,
and blood vessel walls rip during angioplasty. Even for those
deformations used to change anatomical position or shape, damage to
the tissue can be larger than desired; for example, a fibrous
capsule might tear when stretching is preferred.
[0209] Many biological materials are viscoelastic, so they exhibit
time-dependent mechanical properties (Wainwright, Biggs et al.
1976; Woo, Manson et al. 1999; Provenzano, Lakes et al. 2001;
Vanderby and Provenzano 2003; Yin and Elliott 2004; Erdogan,
Erdogan et al. 2005).
[0210] One behavior of biological complex materials that has not
been considered in the design of retractors is "work" or "stress"
softening. Work softening is evident during cyclic
loading/unloading and is characterized as a reduction in the force
at a given deformation during successive cycles, relative to the
initial loading. Viscoelastic materials exhibit stress softening,
but the initial stiffness recovers with rest for most
non-biological viscoelastic materials (e.g. filled rubbers). For
many biological materials, initial stiffuess is not recovered,
reflecting changes in the non-viscous components of the material,
thought to arise from the irreversible dislocation of components
(such as the unentanglement of tangled polymers), from plastic
deformation of polymeric components, or from failure of microscopic
components (such as the fracture of single molecules). The
underlying phenomenology of stress softening is not well understood
(Horgan, Ogden et al. 2004), especially for biological materials
(Vincent 1975; Weisman, Pope et al. 1980; Fleck and Eifler 2003;
Kirton, Taberner et al. 2004; Kirton, Tabemer et al. 2004; Speich,
Borgsmiller et al. 2005; Chaudhuri, Parekh et al. 2007; Dorfmmm,
Trimmer et al. 2007). Nevertheless, the generally observed
phenomenon of work softening, or any change in material property
when subjected to oscillating loading, can be exploited.
[0211] Thus, an alternate means of deforming tissue, relative to
traditional unidirectional loading, is to cyclically load the
tissue. For example, the blades of a retractor move forward and
backward, or an angioplasty balloon cyclically inflates and
deflates.
[0212] Oscillatory motion provides at least three benefits. First,
it can "work soften" the material, decreasing the forces required
to achieve a deformation. Second, oscillatory motion can be used to
measure the viscoelastic parameters of the material (elastic and
viscous moduli), and the results of these measurements can
optionally be used to guide additional manipulations of the tissue.
Third, a large number of small deformations in series can lead to
small scale failure of components thus avoiding catastrophic
failure of the entire structure --similar to the release of energy
at a geologic fault line by many small tremors as opposed to one
large earthquake.
[0213] Note that oscillation can be at different frequencies. A
frequency sweep can be used to identify a harmonic. "White noise"
can be used in dynamic analysis to determine multiple resonant
frequencies that can arise from the composite nature of biological
materials. Oscillation can be conducted at two different
frequencies, either one following the other or with both
frequencies superimposed, to act upon different components of the
composite material comprising the tissue. For example, a lower
frequency can be used to work soften a ligament and a higher
frequency can be used to work soften a polymer by vibrating the
molecules in the polymer. These frequencies can be fractions of a
Hertz to a megaHertz. Thus, oscillations can include mechanical
vibrations, acoustic vibrations, ultrasound, and any other
reciprocating motion.
B.1 Reduction of the Force of Retraction & Reducing
Catastrophic Failure
B.1.1 Tissue Spreaders and Retractors
[0214] Oscillatory motion of a spreader or retractor can be
generated in many different ways, depending on the necessary
frequency and amplitude of actuation, which when coupled with the
force of retraction and the mass of the oscillating system
(retractor blade and tissue) determine the power requirements for
the motor or other actuator.
[0215] For the following discussion, two motions are defined:
[0216] 1. the retraction motion, which is the overall, or average,
motion during the first phase of retraction that is used to achieve
the final deformation of the tissue; and [0217] 2. the oscillation
motion, which is a motion that is superimposed on the retraction
motion.
[0218] As shown in FIG. IIA, the two motions can be performed
separately in time, with a retraction motion B4 proceeding to a
given separation and then pausing, followed by an oscillation
motion B2. Alternatively, as shown in FIG. liB, the retraction
motion B4 and the oscillation motion B2 can be superimposed in
time, thus the retraction motion B6 would be a near-zero frequency
component of the motion, and the oscillation motion would be the
higher frequency component.
B.1.1.1 Experimental Results from Oscillating Loading of
Tissues
B.1.1.1.1 An Example of a Retractor for Oscillating Motion
[0219] A retractor is shown in FIG. 12 that uses a bi-directional
ball screw BIO (i.e., having two bearings that travel in opposite
directions) that is driven by a stepper motor B8, which here is an
MDrive 23Plus made by Intelligent Motion Systems, Inc. The
bi-directional ball screw B10 is mounted to a rail B14 with two
linear translation stages B12, which here are LWHG 25 made by IKO,
such that each translation stage B12 attaches to one of the
bearings of the bi-directional ball screw BIO, thus when the
bi-directional ball screw B10 is rotated by the motor B8, the
translation stages B12 travel in opposite directions. A retractor
arm B18, fabricated by hand from mild steel angle iron that was
cut/bent/welded into shape, is mounted to each translation stage
B12. Each retractor arm B18 has a retractor blade B20 that is
fabricated by hand with mild steel.
[0220] A linear potentiometer B16, which in this case is a 5 k0hm
100 mm made by Schaevitz, is used to measure separation of the
retractor blades B20. The static mount of the potentiometer B16 is
affixed to the rail B14, and the piston of potentiometer B16 is
affixed to one of the translation stages B12. Note that any means
of measuring displacement can be used here, such as optical
encoders, contact and non-contact proximity sensors, digital
calipers, and the like.
[0221] The retractor blades B20 are instrumented with a full-bridge
strain gauge assembly which includes two (2) gauges, which in this
case are model CEA-06-125UN-350 made by Vishay Micro-Measurements,
on each side of each retractor blade B20. The signal from the
strain gauges is then amplified by a signal conditioner (not shown)
which in this case is a Model OM-2 from 1-800-LoadCells. Note that
force can be measured by any of several means, such as drive
current on the motor (and other means of measuring torque on the
drive mechanism), fiber optic strain gauges, optical sensors of
deformation, and the like.
[0222] All signals from the potentiometer B16 and the signal
conditioners/strain gauges are read by a Windows-based computer
using a data acquisition card, which in this case is a National
Instruments Model USB-6211 and software, such as LabVIEW made by
National Instruments, with software prepared by Katya Prince of
Prince Consulting.
[0223] The stepper motor B8 is controlled with IMS Terminal
software, made by made by Intelligent Motion Systems, Inc. Note
that a servo-motor can also be used.
[0224] The strain gauges were calibrated by hanging known weights
from each blade B20 of the retractor. The linear potentiometer B16
was calibrated with a metric ruler.
B. 1.1.1.2 Experiments
[0225] A series of experiments were conducted with the retractor
presented in FIG. 12 using parts from pig cadavers. The parts were
a "front quarter" purchased from Nahunta Pork Center (Pikeville,
N.C.). A front quarter is basically a whole pig cut at the waist
(forming a front half) and split down the vertebrae (forming left
and right quarters); thus, each quarter had an intact rib cage (one
side), spine (bisected), and shoulder. All parts had been
refrigerated after slaughter, used within 24 hours of slaughter,
and warmed by immersion in warm water (while wrapped in a plastic
bag to prevent soaking of the tissue) to near body temperature
(31.degree. C. to 37.degree. C.). The quarters ranged in size from
8 to 12 kg.
[0226] Thoracotomies were performed between three (3) to four (4)
rib pairs on each quarter, almost always performing an incision
between ribs five (5) and six (6), seven (7) and eight (8), nine
(9) and ten (10), and eleven (11) and twelve (12). Thoracotomies
were performed by: [0227] cutting the skin with a scalpel over the
range of the thoracotomy; [0228] bisecting the muscles overlying
the ribs with a scalpel; [0229] cutting through the intercostal
tissues with a scalpel; [0230] pushing a finger between the ribs to
make a small opening; [0231] inserting the closed blades of the
retractor into the opening; [0232] positioning the retractor such
that the blades sat just dorsal of the midline and its axis of
opening were parallel with the midline; and [0233] initiating
opening according to a specified algorithm via computer control of
the stepper motor.
[0234] Incisions were typically 110 mm to 130 mm long, with longer
incisions being performed on larger quarters.
[0235] Experimental retractions with the retractor shown in FIG. 13
are the first simultaneous measurements of force and displacement
during thoracic retraction.
[0236] FIG. 13 shows the displacement B21 of the blades B20 (i.e.,
the distance between the blades B20), and force B22 on one blade
B20 with respect to time for a "standard retraction", similar to
that defined by Bolotin et al. (Bolotin, Buckner et al. 2007),
which proceeds as follows: [0237] a first move, opening to 40 mm in
one (1) minute (2/3 offinal opening), [0238] pause 2 minutes for
force relaxation, [0239] a second move, opening to 60 mm in three
(3) minutes (to the final opening).
[0240] Thus, a total opening of 60 mm is reached in 6 minutes in
this example. Retraction was of a fully automated--the computer
controlled the motor B8, and the motor drove the blades B20 apart.
Each of the two moves is constant velocity (40 mm/min for the first
and 6.8 mm/min for the second). This somewhat matches the pace
described by thoracic surgeons, but there is no standard clinical
practice. Surgeons use a procedure defined by their training,
personal experience, patient condition, and estimates of force
applied at the handle of a hand-cranked retractor. Force
relaxation, as described by Buckner and Bolotin (Buckner and
Bolotin 2006; Bolotin, Buckner et al. 2007) is evident during a
two-minute pause B23--the force required to maintain the 40 mm
opening decreases with time. The points on the force B22 marked
with arrows B24 mark significant tissue breaks, as evidenced by the
change in the force/time slope and by audible "snaps" during the
retraction.
[0241] FIG. 14A shows a retraction in which the displacement B21 is
shown by the upper trace, and force B22 on one blade is shown by
the lower trace. There are four small retractions B25 (2 mm each
over 10 seconds, velocity=0.2 mm/is) of which the second two were
followed by pauses B26 of approximately 50 seconds and the first
two were followed by pauses B27 of 50 seconds interrupted by
oscillation motions B28. The oscillation motions B28 were 11 Hz
with one (1) mm amplitude, 400 cycles, and given the high frequency
of oscillation, they appear on the displacement trace as thickened
regions of the trace. Force relaxation was seen for each of the
four pauses B26, B27, as evidenced by the decrease in force that
follows the onset of each pause. During each oscillation motion
B28, the force oscillated with each cycle of opening/closing.
Importantly, when the force minima are examined over successive
cycles, the force dropped rapidly.
[0242] FIG. 14B shows what the force/time curve looks like when
only the force minima are considered--there is an accelerated force
relaxation (AFR) B30, during the oscillation motions B28, as
illustrated by the grey regions in FIG. 14B. Thus, while the force
declined during normal force relaxation (NFR) B32, as depicted
during the two-minute pause in FIG. 13 and during the 3rd and 4th
pauses B26 in FIG. 14B, the force declined much more rapidly during
the AFR B30 (1st and 2nd pauses B27 of FIG. 14B) than during the
NFR B32. Also, the AFR B30 had a larger magnitude when the
oscillation motion B28 was initiated earlier in the pause, as
evidenced when the 2nd pause/oscillation motion B28 is compared to
the 1st pause/oscillation motion B28--the oscillation motion B28
started sooner in the 2nd pause oscillation and a larger AFR B30
was seen.
[0243] FIG. 15 shows a retraction in which a different trajectory
is followed than for a standard retraction, which is called an
"oscillating retraction" for this discussion. Displacement, or
separation of the blades B20, is shown by trace B36. Force on one
blade B20 is shown by trace B38. During the experiment depicted in
FIG. 15, the incision was opened and oscillated repeatedly. Three
general features observed during oscillating retractions like this
are: [0244] 1. the retraction force does not peak as high as is
seen during the first opening of the standard clinical pace
retraction (compare to FIG. 13); [0245] 2. the maximum force during
oscillating retraction is frequently lower than the maximum force
in a standard clinical pace (compare to FIG. 13); and [0246] 3.
there are fewer large, obvious breaks during oscillating
retractions than during standard clinical pace retractions.
[0247] The latter point is shown in FIG. 13 where breaks B24 are
marked with arrows B24--the breaks appear as rapid changes in the
slope of the force/time trace that are almost always accompanied by
loud snaps or cracks. These events are common during standard
retractions, especially in the final 20 seconds of the first,
one-minute opening and during the last two minutes of the second,
three-minute opening. These rapid changes in slope, accompanied by
loud snaps or cracks, are almost never seen/heard during
oscillating retractions. This point is especially important in
light of the tissue trauma that is frequently observed during
normal surgical practice-broken ribs, dislocated costo-chondral
joints, and torn ligaments and tendons (Vander Salm, Cutler et al.
1982; Greenwald, Baisden et al. 1983; Baisden, Greenwald et al.
1984; Woodring, Royer et al. 1985; Bolotin, Buckner et al. 2007;
Lewis 2007).
[0248] Thus, there are several advantages conferred by oscillating
retractions: [0249] 1. accelerated force relaxation rapidly
decreases the force required for opening; [0250] 2. the large peak
in force seen during the first, one-minute opening of a standard
retraction is not evident; [0251] 3. the maximum force experienced
during retraction is frequently smaller during oscillating
retraction; and [0252] 4. there are fewer, large tissue breaks
during oscillating retraction.
[0253] All of these advantages can result in reduced tissue trauma
during retraction.
B.1.1.2 Single-Actuator Retractors
[0254] FIG. 16 shows a Finochietto retractor in the prior art
(similar to retractor A2 in FIG. 2). It has a fixed retraction
element B44 attached to a rack B45 of a rack-and-pinion drive B46.
A moveable retraction element B42 is attached to the rack and
pinion drive B46 that drives motion B52 of the moveable retraction
element when manual handle B48 is rotated. Each of the retraction
elements B42, B44 has a single blade B40 (similar to blade A4 in
FIG. 2) that engages the tissue to be retracted.
[0255] One way to implement a retractor with both a retraction
motion and an oscillation motion is to use a single actuator that
drives both the retraction and the oscillation motions, such as the
retractor shown in FIG. 12.
[0256] FIG. 17 shows another embodiment of a single actuator
retractor, in which a motor B60 replaces the hand crank B48 of a
typical Finochietto-style rack-and-pinion retractor. The motor B60
can be any motor appropriate for generating the desired motions
B52, such as a servo-motor or a stepper motor. The instructions to
the motor generate any desired motions for retraction motions as
well as oscillations for oscillation motions. Thus, the retractor
can perform retraction and oscillation motions that either are
separated in time or are superimposed in time.
[0257] FIG. 18 shows another embodiment in which the
rack-and-pinion drive B46 is replaced with a lead screw B62 turned
by a motor B74, either a stepper motor or a servomotor. The motor
B74 moves the moveable retraction element B70 with respect to fixed
retraction element B72 to achieve the desired motion B68. Control
of the motor B74 can be either on-board with the motor B74 or
off-board connected by an electrical cable B76.
[0258] In yet another embodiment shown in FIG. 19, the
rack-and-pinion drive B46 is replaced by a hydraulic cylinder B82.
A pressure pump B94 is connected to a pressure reservoir B88 by a
pressure hose 92, and the pressure reservoir B88 is connected to
the hydraulic cylinder B82 by a pressure hose B84. Pressurization
of the hydraulic fluid in the pressure pump B94 pressurizes the
pressure reservoir B88 that feeds the hydraulic cylinder B82 which
forces a moveable retraction element B78 and a fixed retraction
element B80 apart. A pressure gauge B86 reports the pressure in the
system, and a bleed valve B90 permits release of pressure.
Oscillation of the pressure in the hydraulic fluid generates the
oscillation motion. Oscillation can be driven by one of several
means, such as a piston B85 attached to pressure reservoir B88 that
is driven in and out by motor B87.
B.1.1.3 Dual-Actuator Retractors
[0259] The retraction and oscillation motions can be generated by
separate actuators. For example, a first actuator drives the
retraction motion, and a second actuator drives the oscillation
motion. This confers several advantages: [0260] different actuators
can be matched to the different power requirements for the two
different motions; [0261] different actuators can be matched to the
displacements required for the two different motions; and [0262]
different distributions of masses are permitted, e.g. removing
bulky components required for the large amplitude motions of the
retraction motion from the components that must be driven at higher
frequency but lower amplitude for the oscillation motions.
[0263] In one embodiment shown in FIG. 20, a retraction motion is
generated by a first actuator which in this example is a
rack-and-pinion drive B98 driven by hand crank B99 along a rack
B100 on a conventional Finochietto-style retractor. The first
actuator moves a moveable retraction element B101. The oscillation
motion B102 is generated by a motor-driven acentrically mounted cam
B104 that rides on two surfaces, a first surface B106 attached to
the rack B100 of the retractor and a second surface B107 attached
to an oscillation motion element B108 that is mounted to the rack
B100 by a hinge B109. When the acentrically mounted cam B104
rotates, the oscillation motion element B108 oscillates with motion
B102 with the frequency of rotation of the motor and with amplitude
determined by the diameter and acentricity of the cam B104 and the
lever-arm of the oscillation motion element B108.
[0264] In another embodiment shown in FIG. 21, a hand-cranked
rack-and-pinion drive B110 is used for performing the retraction
motion. A second actuator B112 drives the oscillation motion. The
second actuator B112 presented here is a thin hydraulic cylinder or
pressure pad 13120 mounted on each retractor blade B114 and is
driven by a hydraulic system capable of generating the necessary
pressures and volumes to drive the requisite motion. In this
example, a pressure hose B124 attached to pressure pads B120 and to
an external pressure source (not shown) permits cyclic oscillation
of the pressure pads B120 via an oscillating flow B126 of fluid.
The second actuator B112 could be any actuator that mounts to the
retractor blades B8114 of retraction elements B116, B18, such as a
voice coil, a linear motor, a hydraulic cylinder or other actuator
capable of generating the oscillation motion. A semi-transparent
view of a retractor blade 114 is provided to allow a more complete
view of the assembly.
[0265] In another embodiment shown in FIG. 22, a retractor has a
motorized lead screw drive B130 that drives along the lead screw
B132 for the retraction motion. Voice coils B134 mounted onto
blades B136 of the retraction elements drive an oscillation motion
B138.
B.1.1.4 Multiple-Actuator Retractors
[0266] FIG. 23 shows an embodiment in which a retractor B140 with
multiple arms and actuators can apply oscillating loads. The
retractor B140 has a frame B 42 to which independent actuators B144
and arms with attached blades B146 are mounted. The actuators B144
can be motors, hydraulic cylinders, or other appropriate actuators
and can be actuated by one of a variety of methods, including all
moving in synchrony, opposing pairs of actuators B144 or other
functional groupings of actuators B144 moving in synchrony but not
in synchrony with other functional groupings of actuators B144, or
all actuators B144 moving independently. The actuators B144 perform
both the retraction motion and the oscillation motion. The
actuators B144 can be wire or cable wound onto a spool that is
driven by a servo-motor or by a manually driven worm drive, with
the blades B146 of the retraction elements attached to the wire or
cable. Optionally, the retractor B140 can be instrumented with
sensors that measure the force on the blades B146 of the retraction
elements, or the displacements of the blades B146 of the retraction
elements, or any other parameter relevant to the motion of the
blades B146 of the retraction elements. The output from the sensors
can be displayed by indicators B148 on the frame of the retractor
B142 or on the monitor of a computer attached to the retractor B140
via an electrical cable B150.
[0267] FIG. 24 shows another embodiment of a retractor B160 with
multiple arms and actuators. Here there is a first actuator that
generates the retraction motion by separating two halves B162, B164
of the retractor frame that resembles a Finochietto-style
retractor.
[0268] This first actuator is a rack-and-pinion B166 driven by a
hand crank, but, optionally, could be driven by a motor or other
appropriate actuator. Additional actuators B168 attached to both
halves B162, B164 of the retractor frame drive the oscillation
motion of retractor blades B170. The additional actuators B168 can
be driven by any appropriate actuator, such as a motor, a voice
coil, a piezoelectric driver, or a hydraulic actuator. The
additional actuators B168 can be rack-and-pinion in which the
retractor blades B170 are attached to the rack. The additional
actuators B168 can be wire or cable wound onto a spool that is
driven by a servo-motor with the cable attaching to the blade B170
of the retraction element. Alternatively, the actuators can be
linear motors.
B.1.2 Angioplasty Balloons and Stents
[0269] Another common actuator for deforming anatomical tissues is
the balloon used for angioplasty with or without placement of a
stent. The deflated balloon is inserted via a catheter into the
blood vessel to be enlarged, and the balloon is inflated such that
it presses against the walls of the blood vessel, enlarging the
radius of that portion of the blood vessel. Similar methods are
used in valvuloplasty, where the diameter of a heart valve is
enlarged. Similar methods are used in tuboplasty to enlarge
portions of the urinary tract and other surgical procedures to
enlarge tubular anatomical elements, such as biliary tubes.
[0270] In the prior art, motions of the balloons are
one-directional--they are simply inflated with a sterile fluid.
Sometimes several balloons of increasing diameter are used to
enlarge the anatomical element in increments, but each balloon is
simply opened.
[0271] For angioplasty and valvuloplasty, inflation of the balloon
is similar to the "retraction motion" described earlier for
retractors. We present inventions to impose an "oscillation
motion", as described above. To simplify the following discussion,
each cycle of oscillation is divided into an "inflation phase" and
a "deflation phase".
[0272] In one embodiment depicted in FIG. 25, an angioplasty
balloon B200 is inflated by a sterile fluid that passes through a
catheter B202 from a first syringe B204 that is used to generate
the pressure to inflate the balloon B200: The retraction motion is
inflation of the balloon B200, which is driven by the plunger B206
of the first syringe B204. These retraction motions are shown in
solid black, single-headed arrows. A second syringe B210 is also
connected to the catheter B202. A plunger B212 of the second
syringe B210 oscillates in and out, cycling a pressure that drives
the oscillation motion of the balloon B200. The oscillation motion
of the balloon B200, and the associated oscillating drive of the
plunger B212, are shown as asymmetric, double-headed arrows with
one arrow shape depicting the inflation phase and the other arrow
shape depicting the deflation phase. Thus, oscillation of the
pressure is achieved with a reciprocating motion of the plunger
B212 such that the plunger B212 stroke length determines the
amplitude of the oscillation and the pltmger B212 stroke frequency
determines the frequency of the oscillation motion. Motion of fluid
during the deflation phase can be driven both by the combined
elastic strain in the wall of the balloon B200 and in the wall of
the anatomical element and by the rearward motion of the plunger
B212.
[0273] In another embodiment depicted in FIG. 26, motion of fluid
up the catheter B202 for inflation of the balloon B200 is driven by
a first syringe B204 as described for FIG. 25. The oscillation
motion is driven by a piston B224 that impinges on a drive membrane
B222 separating fluid from the piston B224. This separation of
fluid from the piston B224 facilitates cleaning and sterilization
of the moving parts for maintenance of sterility of the fluid.
During the oscillation motion, the motion of fluid up the catheter
B202 during the inflation phase is driven by the piston B224.
Motion of fluid in the opposite direction during the deflation
phase is driven by the combined elastic strain in the wall of the
balloon B200 and in the wall of the anatomical element and by
rearward motion of the piston B224.
[0274] One limitation of driving the inflation and deflation
motions of the fluid up and down the lumen of the catheter is the
resistance to fluid motion imposed by the long, narrow catheter
lumen. This high resistance to fluid motion limits the frequencies
and amplitudes attainable for the oscillation motion.
[0275] One means of eliminating the limitation is to restrict fluid
motion during both phases of the oscillation motion to short
distances through larger diameter connections. This is achieved in
the embodiments depicted in FIGS. 27 and 28. Consider FIG. 27, the
balloon has two compartments. A first larger diameter compartment
B207 functions to force the anatomical element B211 open (see FIG.
27C), and a second smaller diameter compartment B206 functions as a
fluid reservoir. Second compartment B206 can be placed upstream, as
depicted, or downstream from the first compartment B207. Fluid
flows easily between the two compartments through connecting
channel B208. The retraction motion is driven, as in the prior art,
by pumping fluid up the catheter B212 to inflate the first
compartment B207. The oscillation motion is generated by forcing
fluid back and forth from the second compartment B206 to the first
compartment B207. The oscillation motion is thus driven by a second
actuator, comprising the second compartment B206.
[0276] One means for driving the motions of the second compartment
B206 is shown in FIG. 28A. FIG. 28B shows an enlarged view of
second compartment B206. The second compartment B222 can be
helically wound B226 with a wire or cable made of a shape memory
material, such as Nitinol. Electrical actuation of the Nitinol
decreases the diameter, and thus the volume, of the second
compartment B222, forcing fluid through connecting channel B208
into the first compartment B207 to drive the inflation phase of the
oscillation motion. The deflation phase is then driven by the
combined elastic strain in the wall of first compartment B207 and
the wall of the anatomical element. The elastic strain driving the
deflation phase can also be augmented by a second helical wind (not
shown) of spring material around the first balloon compartment
B207.
[0277] In another embodiment depicted in FIG. 29, the angioplasty
balloon B230 has a single compartment B232 and is shaped as a
cylinder, and the oscillation motion is generated in the walls of
the compartment B232. FIG. 29A shows compartment B232 deflated, and
FIG. 29B shows compartment B232 inflated. Compartment B232 is
inflated by flow B234 through catheter B212, driving the retraction
motion. The two phases of oscillation motion are driven by a first
helical wind B236 of shape-memory material, such as Nitinol, and a
second helical wind B238 of an elastic spring material. The first
helical wind B236 of shape-memory material causes the cylindrical
compartment B232 to decrease diameter (and elongate to maintain
constant volume), thereby driving the deflation phase. The second
helical wind B238 of spring material stores elastic strain energy
during the deflation phase that then drives the inflation phase
when electrical actuation of the first helical wind B236 ends.
Similarly, the two helical winds B236, B238 can be wound such that
electrical actuation of the first helical wind of shape-memory
material increases the diameter of the balloon driving the
inflation phase, and elastic energy storage in the second helical
wind of material decreases the diameter of the balloon driving the
deflation phase. Furthermore, shape memory material and elastic
spring material can be included in the first helical wind B236 and
in the second helical wind B238 such that actuation of one helical
wind B236, B238 and then the other helical wind B236, B238 drives
both phases of oscillation. Furthermore, only shape memory material
can be included in the first helical wind B236 and in the second
helical wind B238 such that actuation of one helical wind B236,
B238 and then the other helical wind B236, B238 drives both phases
of oscillation.
[0278] In another embodiment depicted in FIG. 30A, the angioplasty
balloon B250 has a single compartment B252 and the oscillation
motion is driven by a bubble generated inside the compartment B252.
The retraction motion is driven by inflation of the compartment
B252 by fluid motion up the lumen of the catheter B212. The
oscillation motion is driven by a small electrical heater B254
mounted onto a wire B256 inside catheter B212 underlying the
compartment B252 such that a bubble B258 of water vapor is formed,
driving the inflation phase of the oscillation motion. Heat
dissipation to the surrounding fluid and tissue causes the vapor
bubble B258 to collapse, driving the deflation phase of the
oscillation motion. Similarly, electrolytic bubble generation of a
bubble B258 inside the compartment B252 could drive the oscillation
motion.
[0279] In another embodiment depicted in FIG. 30B, high frequency
of oscillation is generated by a piezoelement. Angioplasty balloon
B270 has a single compartment B272 and the oscillation motion is
driven by a piezo-vibrator B274 mounted on a wire B276 inside the
compartment B272. The retraction motion is driven by inflation of
the compartment B272 by fluid motion up the lumen of the catheter
B212. The oscillation motion is driven by actuation of
piezo-vibrator B274 which emits high-frequency pressure waves B280
which transmit as high-frequency, low-amplitude oscillations of the
wall of compartment B272.
B.2 Measurement of Tissue Properties
[0280] Oscillating deformation of a tissue with simultaneous
measurement of selected parameters (e.g., force, displacement) can
yield important information about the tissue's material properties
and physiological state.
[0281] Leveque et al. (Leveque, Rasseneur et al. 1981) disclose
oscillating loading for measurement of the Young's modulus and the
internal damping factor of a viscoelastic material, including
excised biological tissues, by oscillating loading. Long et al.
(Long 1992; Long, Pabst et al. 1997) disclose measurement of the
dynamic bending stiffness and damping coefficients of isolated
intervertebral joints that are loaded by oscillating bending.
[0282] There are two disclosures for measuring the mechanical
properties of an intact biological tissue: [0283] 1. Brown and
Holmes (Brown and Holmes 1990) disclose a method for measuring the
mechanical properties of intact tissues, and they disclose only
constant velocity deformation as a means for standardizing
measurements for spinal instability; and [0284] 2. Huszar (Huszar
1984) discloses a modified version of the technique of Leveque et
al. (Leveque, Rasseneur et al. 1981) to make a measuring device
that applies a force on the uterine cervix to measure the modulus
of extensibility of the tissue in situ; the purpose is to assess
the status of the cervix during obstetric procedures, especially
for pregnancy, and Huszar also suggests use for ear or skin.
[0285] Measurements on intact tissues, as opposed to excised
tissues, limits direct applicability of the above techniques
disclosed for measuring mechanical properties by oscillating
loading. This is due to the unknown dimensions of the intact
tissues, unknown mass and connectivity to surrounding tissues, etc.
However, modifications we disclose permit the collection of
information relevant to the mechanics and physiology of the tissue
being retracted or dilated. Importantly, these modifications can
provide information relevant to the processes of retraction or
dilation.
[0286] In one embodiment, as disclosed in Section B.1.1.1 and shown
in FIG. 12, simultaneous measurement of force and displacement
during oscillating loading permit measurement of effective
stiffness (the slope of force/distance of displacement) and of
viscous losses (area bound by hysteresis of the force/displacement
curve seen during one cycle of loading/unloading). Furthermore,
accelerated force relaxation APR can be measured as disclosed in
Section B.1.1.1.2 and shown in FIG. 31 to determine when to end an
oscillation period. As shown in FIG. 31, a time constant D for
accelerated force relaxation APR can be determined by fitting a
decay curve to the minimum force points for each oscillation, and
cyclic loading can then be terminated when a fraction of the time
constant has expired. For example, when retracting a tissue, the
following sequence of steps can be followed: [0287] (1) a
retraction motion B300 is performed; [0288] (2) retraction is
paused; [0289] (3) an oscillation motion B302 is performed with
measurement of force and real-time calculation of the time constant
D D D D D D D of the force relaxation as shown in FIG. 31; such
that when a time equal to the time constant D D D D D D D has
elapsed; [0290] (4) oscillation motion B302 ceases; and [0291] (5)
retraction motion B300 resumes. This algorithm can be used to
optimize the reduction of force during a retraction (maximum force
decrease in the smallest amount of time). Similarly, the
oscillation can be stopped when some fraction or multiple of the
time constant is achieved. Conversely, the force decrease can be
monitored, and the oscillation motion terminated when the force has
declined by a specified amount or percentage of the starting
force.
[0292] In another embodiment shown in FIG. 32, decline in effective
stiffness of a tissue can be measured arising from oscillating
loading via phenomena such as work softening. Effective stiffness
(force/displacement, dF/dx where F is force and x is distance)
decreases in a tissue that displays work softening. Measurement of
force and distance during repeated cycles of loading/unloading
permit comparison of stiffness during each successive loading (or
unloading). Thus, as shown in FIG. 32, which shows two (2) cycles
of loading, the force displacement trace begins at B310 and ends at
B312. As an example, the effective stiffness of the material during
the first cycle of loading is estimated as the slope of the line
B314, drawn between the limits of minimum and maximum displacement
for that cycle, and, again, during the second cycle as the slope of
the line B316. The decrease in slope from line B314 to line B316 is
then used as an estimate of the degree of work softening.
Comparisons of effective stiffness can be made repeatedly, in real
time, during oscillating loading. The embodiment of a retractor
described in Section B.1.1.1 would serve for such measurements.
Another embodiment would be an angioplasty balloon in which
pressure and volume in the balloon are measured during oscillating
loading, such that volume is used as an estimate of displacement
and pressure is used as an estimate of force. Pressure can be
measured with any appropriate pressure gauge. If loading is at a
low frequency, then measurement anywhere in the fluidic system
would suffice because pressure gradients that drive flow into the
balloon would be small. If loading is at higher frequencies, the
measurements can be made inside the balloon with several methods
including miniaturized pressure sensors (membrane deflection,
capacitance based, etc.) Volume can be measured by measuring the
displacement of fluid in the balloon by means such as piston
displacement, or with a mass flow sensor placed along the channel
to the balloon. The diameter of the balloon can also be used to
directly determine deformation of the anatomical part or to
estimate the volume of the balloon. The diameter of the balloon can
be measured acoustically or optically via reflection of radiation
off the wall of the balloon.
[0293] Viscous losses during deformation of the tissue can be
estimated by any of several methods, including: measuring the phase
lag between force and displacement, measuring the area bound by the
hysteresis curve during one cycle of loading/unloading, or
measuring the difference in work performed by the motor during
loading and unloading.
[0294] The resonant frequency of the materials may be measured by
oscillating at different frequencies as disclosed by Leveque et al.
(Leveque, Rasseneur et al. 1981), by identifying the frequency at
which the force required for deformation is smallest, by
identifying the frequency at which viscous loss is smallest, or by
other methods known in the fields of mechanics and
biomechanics.
[0295] Many methods of testing by oscillation require testing at
multiple frequencies of oscillation. This can be accomplished by
testing at multiple discrete frequencies, testing via a frequency
sweep, or testing with "white noise".
B.3 Tissue Deformation Via Oscillating Loading, Tissue Measurement,
and Feedback
[0296] Information obtained by measurements such as those disclosed
in Section B.2 can be used to make decisions about how best to
perform a tissue deformation by either oscillating loading (e.g.,
an oscillation motion) or normal one-directional loading (e.g., a
retraction motion).
[0297] In one embodiment, force and displacement are measured by a
retractor.
[0298] Alternating retraction motion and oscillation motion are
used. A retractor similar to that in Section B.1.1.1.1 and shown if
FIG. 12 can be used. The first phase of retraction proceeds as
follows: [0299] (1) The retraction motion starts, during which the
distance is measured, and the retraction motion is stopped when a
fraction of the desired opening is reached, e.g. 10% or 30%; [0300]
(2) Oscillation motion is then imposed to determine the frequency
that results in the smallest time constant D for accelerated force
relaxation (AFR). [0301] (3) Oscillation motion is then continued
for a duration of 1.5 D and then stopped; and [0302] (4) Retraction
motion is resumed.
[0303] This cycle is repeated, possibly with different opening
extents (e.g. another 10% of desired opening or another 20% of
desired opening) until the desired opening is obtained.
[0304] In another embodiment, the stiffness of the material is used
to determine when an oscillation motion begins. Force (F) and
distance (x) are measured by the retractor, and stiffness is
measured in real-time as dF/dx. Alternating retraction motion and
oscillation motion are used as described in the preceding
paragraph. Retraction proceeds as follows: [0305] (1) Retraction
begins with a retraction motion, and stiffness is measured
throughout motion. When stiffness starts to decrease, indicating
the material properties of the tissue are changing, retraction
motion stops; [0306] (2) Oscillation motion commences with an
amplitude of approximately 2 mm and a frequency of approximately 5
to 10 Hz, or with an amplitude of approximately 4 to 8 mm and a
frequency of approximately 0.5 to 2 Hz; [0307] (3) Oscillation
occurs for approximately 10 to 50 cycles to alter the material
properties of the tissue such that stresses in the tissue are
relieved and large-scale tissue components don't break; and [0308]
(4) retraction motion is resumed.
[0309] Other frequencies and amplitudes can be used, and frequency
and amplitude can be adjusted for the tissue to be retracted, with
bone, for example, being oscillated at a frequency of kHz and an
amplitude of micrometers. The oscillation motion can be any
combination of frequency and amplitude that achieves appropriate
modification of the tissue being retracted.
[0310] In another embodiment, retraction and oscillation motions
are superimposed. Retraction follows a pre-determined trajectory
(e.g., a trajectory in which the retractor blades move apart
quickly at first but increasingly slowly as retraction proceeds
such that the desired opening is achieved in a proscribed time,
such as that shown in FIG. 11B).
[0311] Force and distance are measured. Oscillation serves both to
accelerate force relaxation, which now occurs concomitantly with
continuous deformation, and to permit repeated stiffness
measurements, as shown in FIG. 32) to regulate the velocity of the
retraction motion about the predefined trajectory (e.g., if
stiffness is too high, then the velocity of the retraction motion
slows, or if the stiffness is too low, then the retraction motion
accelerates).
[0312] In another embodiment, pressure in the tissue is measured by
a catheter sensor, such as the miniaturized sensors from Scisense,
Inc. of London, ON, Canada and ADInstruments of Colorado Springs,
Colo., USA. One or more pressure sensors are placed into the tissue
near the retractor blades, such that the pressure sensors sense
internal tissue pressure and how internal tissue pressure rises
during retraction. Alternating retraction and oscillation motions
are used. Retraction motion starts and proceeds until tissue
pressure reaches a threshold (e.g., a level that indicates that
perfusion of the tissue has stopped). Retraction motion is halted
and oscillation motion is started. Oscillation motion is used for
accelerated force relaxation until the pressure drops below the
threshold. Retraction motion is resumed, and the process repeated
until the desired opening is achieved.
C. Detecting Tissue Trauma During Retraction
[0313] FIG. 33 presents an example of a Finochietto-style retractor
C4 in the prior art. The retractor C4 has a fixed retraction
element C6 attached to one end of a rack C8 of a rack-and-pinion
drive C10 driven by a manual drive handle C12. A moveable
retraction element C14 is attached to the rack-and-pinion drive C10
and moves along the rack C8. Each of the retraction elements C6,
C14 has a single blade C16 that engages the tissue to be
retracted.
[0314] A retractor C4, such as that shown in FIG. 33, can be
instrumented to measure several parameters during retraction. For
example, the blades C16 of the retractor C4 can be fitted with
force sensors (such as strain gauges or a load cell), and the
separation of the blades C16 can be measured by fitting a
displacement sensor onto the retraction elements C6, C14 (such as a
linear potentiometer or an optical encoder). The output from these
sensors can be fed into a display (such as a digital numeric
display or a bank of light emitting diodes LEDs) for direct
readout, or the signal can be fed into an analog-to-digital
converter and read by a computer for subsequent calculations and
display. Multiple sensors measuring a parameter (for example, a
plurality of load cells and/or accelerometers indicating forces
and/or accelerations acting on a corresponding plurality of
retractor blades) can provide a map in two dimensions (2D), three
dimensions (3D), or four dimensions (4D, with time) of the forces
and moments acting on the system consisting of the body of the
patient and the retractor C4.
[0315] FIG. 34 depicts the retractor C4 showing how it might be
fitted with a set of calipers C22 for measuring the separation of
the retraction elements C6, C14. Additionally, strain gauges C20
can be placed on each of the two blades C16 of the retraction
elements C6, C14 ("retractor blades") to measure forces on the
retractor blades C16.
[0316] FIG. 35 shows a retractor C28 that uses a bi-directional
ball screw C30 (i.e., having two followers that travel in opposite
directions) that is driven by a stepper motor C32 which in this
case is a MDrive 23Plus from Intelligent Motion Systems, Inc. The
bi-directional ball screw C30 is mounted to a rail C34 with two
linear translation stages C36 which in this case is the IKO LWHG 25
from IKO, Inc. such that each translation stage C36 attaches to one
of the bearings on bi-directional ball screw C30, thus when
bi-directional ball screw C30 is rotated by the stepper motor C32,
the translation stages C36 travel in opposite directions. A
retractor arm C38 fabricated by hand from mild steel angle iron
that was cut/bent/welded into shape, is mounted to each translation
stage C36. Each retractor arm C38 has a retractor blade C40
fabricated by hand with mild steel.
[0317] A linear potentiometer C42 which in this case is a 5 k0hm,
100 mm linear potentiometer from Schaevitz is used to measure
separation of the retractor blades C40. The static mount of the
potentiometer C42 is affixed to the rail C34, and the piston of the
potentiometer C42 is affixed to one of the translation stages C36.
Note that any means of measuring displacement could be used here,
such as optical encoders, contact and non-contact proximity
sensors, digital calipers, and the like.
[0318] The retractor blades C40 are instrumented with a full-bridge
strain gauge assembly (not shown) which includes two (2) gauges,
which in this case are model CEA-06-125UN-350 from Vishay
Micro-Measurements, Inc., on each side of the blade. The signal
from the strain gauges is the amplified by a signal conditioner
(not shown) which in this case was model OM-2 from 1-800-LoadCells.
Note that force could be measured by any of several means, such as
drive current on the motor (and other means of measuring torque on
the drive mechanism), fiber optic strain gauges, optical sensors of
deformation, and the like.
[0319] All signals from the linear potentiometer C42 and the signal
conditioners/strain gauges are read by a Windows-based computer
using a data acquisition card, which in this case is a model
USB-6211 from National Instruments, and software, which in this
case is LabVIEW from National Instruments, Inc. using a custom
program prepared by Katya Prince of Prince Consulting. The stepper
motor C32 is controlled with IMS Terminal software from Intelligent
Motion Systems, Inc. Note that a servo-motor could also be used.
The strain gauges were calibrated by hanging known weights from the
retractor blades C40 of the retractor C28. The linear potentiometer
C42 was calibrated with a metric ruler.
[0320] A series of experiments were conducted with the prototype
retractor C28 described above using parts from pig cadavers. The
parts were a "front quarter" purchased from Nahunta Pork Center
(Pikeville, N.C.). A front quarter is basically a whole pig cut at
the waist (forming a front half) and split down the vertebrae
(forming left and right quarters); thus, each quarter had an intact
rib cage (one side), spine (bisected), sternum (bisected), and
shoulder. All parts had been refrigerated after slaughter, used
within 24 hours of slaughter, and warmed by immersion in warm water
(while wrapped in a plastic bag to prevent soaking of the tissue)
to near body temperature (31.degree. C. to 37.degree. C.). The
quarters ranged in size from 8 to 12 kg.
[0321] We performed thoracotomies between 3-4 rib pairs on each
quarter, almost always performing an incision between ribs 5-6,
7-8, 9-10, and 11-12. Thoracotomies were performed by: [0322]
cutting the skin with a scalpel over the range of the thoracotomy,
and in a direction parallel to the ribs, [0323] bisecting the
muscles overlying the ribs with a scalpel, [0324] cutting through
the intercostal tissues with a scalpel, [0325] pushing a finger
between the ribs to make a small opening, [0326] inserting the
closed blades of the retractor into the opening, [0327] positioning
the retractor such that the blades sat approximately halfway
between the spine and the sternum and the retractor's axis of
opening was approximately parallel with the spine, [0328]
initiating opening according to a specified algorithm via computer
control of the stepper motor.
[0329] Incisions were typically 110 mm to 130 mm long, with longer
incisions being performed on larger quarters.
[0330] FIG. 36 shows data from the retractor C38, with force C50
and displacement C52 (distance measured by the linear potentiometer
C42) plotted with respect to time for a "standard retraction",
similar to that defined by Bolotin et al. (US Patent Application
Publication Number 2006/0025656 and 2007, J. Thorac. Cardiovasc.
Surg. 133:949), which proceeds as follows: [0331] open to 40 mm in
one (1) minute (2/3 of final opening); [0332] pause two (2) minutes
for force relaxation; and [0333] open to 60 mm in three (3) minutes
(i.e., to the final opening).
[0334] Thus, a total opening of 60 mm is reached in 6 minutes. Each
of the two moves is constant velocity (40 mm/min for the first and
6.8 mm/min for the second). These moves were controlled by a
computer program executed in a computer with the IMS Terminal
software. Thus, unlike Buckner and Bolotin et al. (US Patent
Application Publication Number 2006/0025656 and 2007, J. Thorac.
Cardiovasc. Surg. 133:949) the velocity of the retraction motions
was precisely controlled. This somewhat matches the pace described
to us by other thoracic surgeons, but there is no standard clinical
practice. Surgeons use a procedure defined by their training,
personal experience, patient condition, and sense-of-touch (i.e.,
non-quantitative) estimates of force applied at the handle of a
hand-cranked retractor. Furthermore, surgeons have no velocity
control, other than hand-eye coordination. Importantly, the
self-locking Finochietto-style rack-and-pinion drive C10 engages
and advances in rather abrupt half-step turns of the handle CIO,
producing a non-linear relationship between rotation and motion of
the retractor blades C16, making control of velocity and force
difficult.
[0335] FIG. 37 shows the displacement and force on both arms for a
Finochietto retractor instrumented like the retractor shown in FIG.
34, except that a linear potentiometer is used to measure
displacement, instead of the caliper shown in FIG. 34. These
measurements are from a thoracotomy performed on an anesthetized
pig (female, 50 kg weight, procedures similar to those in FIG. 36
except that opening was to 52 mm in one minute without a long pause
in retraction). The force and displacement traces in FIG. 37 are
not smooth. Both traces show the step-by-step increases generated
by the Yz-rotations of the crank. Furthermore, even small
adjustments or other motions of the crank resulted in large
deflections in the force trace. For example, when the surgeon
simply adjusted the position of his hand on the crank at 42 s, an
approximately 30 N change in force is seen in the force trace for
both retractor blades. During this retraction, a rib broke.
Importantly, the point on the trace where the rib broke could not
be identified in any of the traces. The point C56 on the trace
where the rib broke was identified by careful analysis of a
time-correlated video recording of the procedure in which the break
could be heard as a "crack". Thus, it is not possible from these
force or displacement traces to detect that a rib is about to
break. Nor is it possible to determine if a rib breaks.
[0336] Returning to FIG. 36, the force of the motorized retraction
rises rapidly over the first minute of retraction (opening to 40
mm). Force relaxation, as described in Buckner and Bolotin et al.
(US2006/0025656 and 2007, J. Thorac. Cardiovasc. Surg. 133:949),
and also illustrated in FIG. 1, is evident during the two-minute
pause--the force required to maintain the 40 mm opening decreases
with time. Force again rises when retraction is resumed at 3
minutes, rising at a time-varying rate, but the increase in force
is smooth up until 60 mm retraction is achieved.
[0337] No significant tissue breaks occurred during the retraction
shown in FIG. 36. Two small breaks are evident over the first 50-60
s interval, as evidenced by small downward deflections in the force
trace (marked by arrows). The absence of significant breaks is
unusual. Most retractions of this type resulted in large tissue
breaks, as seen in FIGS. 38A-38C and 40A-40B (discussed below).
[0338] FIG. 38A shows data from another retraction, using the same
motorized standard retraction as in FIG. 36. A large break is
seen--a break that spanned several seconds (46-70 s on the graph,
marked with an asterisk) and ended only with the start of the pause
period. There are also several smaller breaks (marked with arrows),
also evident as significant drops in the slope of the force plot.
FIG. 38B shows an expanded view of the data from 20 to 70s, showing
the large break. There are two types of events that precede this
large break. The first type of event is a decrease in the slope of
the curve beginning at 38 s (illustrated by the two dashed
lines--termed a "slope event"). The second type of event is a small
break seen as a drop C60 in force at 42 s, marked with an arrow in
FIG. 38B (termed a "force event"). Note that there is a second
force event C62 at 44 s. FIG. 38C shows the interval from 41.5 to
45 seconds on an expanded scale; the two force events, the first
force event C60 at 42 s and the second force event C62 at 44 s, are
clearly visible.
[0339] The two types of events, slope events and force events,
preceding the large break are better seen in FIG. 39 which plots
both the force (kg) and the slope of the force (kg/s) for the
interval of 10 to 46 s in the retraction shown in FIG. 38. A slope
event C70 beginning at 38 s is more visible, and the two small
breaks are now much more prominent as negative-going peaks marking
the first force event C60 and the second force event C62.
[0340] FIGS. 40A and 40B present another example of a standard
retraction--FIG. 40A presents data from the entire retraction, and
FIG. 40B presents a magnified view of one minute of data from 30 s
to 90 s. In this retraction, there is, again, a large break C100 at
the end of the first 1-minute of retraction, beginning at about 72
s. Several small force events occur (e.g., at 57 s, 59 s, 61 sand
others), but preceding these is a slope event C102 beginning at 57
s. This drop in slope C102 is more obvious than the slope event C70
seen in the retraction shown in FIGS. 38 and 39. The slope event
C102 in FIG. 40 is evident in the force trace, but is more easily
seen in the slope trace. Another common feature is evident
here--both the force trace and the slope trace become noisier;
their variance increases. This provides third and fourth indicators
of an imminent break--termed a "force variance event" and a "slope
variance event".
[0341] All four of these events, (a) a force event, (b) a slope
event, (c) a force variance event, and (d) a slope variance event
are frequently seen preceding a large break and can be used as
indicators that a large break is about to occur.
[0342] Note that higher order time derivatives of the force trace
(e.g., d2F/dt2, etc) also present information relevant to imminent
breaks and can make a distinction from baseline simpler because the
signal stays near zero. FIGS. 41A and 41B show the second time
derivative, d.sup.2F/dt.sup.2, of the force for the retractions
presented in FIGS. 38, 39, and 40. (FIG. 41Aa presents the
retraction from FIGS. 38 and 39, and FIG. 41B presents the
retraction from FIG. 40.) In FIG. 41A, the force event C60 at 42
sand the force event C62 at 44 s are now clearly resolved as
negative-going spikes C200 and C202. In FIG. 41B, the slope event
at 57 s is now clearly resolved as a large, negative-going spike
C210. Thus, the second time derivative of the force provides both
(a) a flat baseline over much of the retraction and (b) a
negative-going spike at force and slope events providing a clear
signal indicating the onset of the variance. Detection of the spike
can be accomplished by comparison of substantially instantaneous
values of d2F/dt2 versus a time-averaged value of d2F/dt2, with the
ratio of instantaneous/time-averaged values of d2F/dt2 exceeding a
predefined threshold, or by comparison of instantaneous values of
d2F/dt2 with variance of d2F/dt2 measured over a preceding time
interval, such as the ratio of the instantaneous value of d2F/dt2
with the sum of squares of d2F/dt2 over the preceding 20 s or over
the preceding 4 s. There are many such detection algorithms
well-established in the art of signal processing that can be used
to detect a negative-going spike in d2F/dt2.
[0343] Implementation of these indicators within automated control
systems in medical devices would permit both (a) the presentation
of indicators to the physician, permitting the physician to take
corrective action before a break occurs, and (b) automated
operation whereby the device contains appropriate mechanisms to
implement corrective action. Software executed by microprocessors
can perform appropriate signal processing (e.g., Butterworth
filter, Fourier analysis, etc.) of signals from sensors to improve
signal-to-noise, and this software can also perform automatic event
detection with automatic response. For example, an automated system
can initiate a pause in the first phase of retraction if a
negative-going spike in d.sup.2F/dt.sup.2 is detected, or an
automated system can initiate an oscillating motion in the first
phase of retraction if a negative-going spike in d2F/dt2 is
detected.
[0344] Importantly, detection of these events requires a stable
force-time trace. This requires a means of regulating the velocity
of retraction to ensure that it maintains a commanded velocity free
of substantial variations in velocity; for example, the retraction
velocity remains constant during measurement, or the trajectory of
motion during the first phase of retraction follows a substantially
parabolic profile, retracting more quickly at first and
increasingly slower as retraction approaches a desired opening of
the surgical incision or a desired dilation of the artery. This can
be accomplished with a retraction system with manual actuation
permitting very smooth motion, such as a hydraulic actuator or a
fine pitched lead screw. Preferably, retraction is performed by a
motor-driven retractor such that velocity can be maintained at
predetermined rates by internal control, such as by an open-loop
system with a stepper motor that is capable of generating
sufficient torque as to not be impeded by retraction forces or by a
closed-loop system with a servo-motor. Closed loop control of
velocity in a hydraulically-actuated system is also possible. The
velocity of retraction can be constant, but this is not necessary.
For example, a smoothly time-varying velocity can be used.
[0345] FIG. 42 depicts an example of an algorithm C300 for
detecting imminent tissue trauma. The algorithm C300 can be used
for any retraction profile (displacement over time) with any device
that measures force. The algorithm C300 searches for both a
negative-going spike in the force trace and for an increased
variability ("noisier") force trace. The user inputs two
thresholds, Ts for detecting the negative-going spike and Tv for
detecting increased variance. The thresholds Ts and Tv allow the
user to set the sensitivity of the algorithm C300. For example, a
surgeon might choose to use a more sensitive setting for a patient
expected to have fragile bones. Variability in the force signal is
calculated as the root-mean-square (RMS) of the force trace, as
shown in FIG. 42. Execution of the algorithm C300 starts (block
C302) at the initiation of retraction. Retraction proceeds for
N+O.1 seconds (block C304), with force sampled at a rate equal to
or greater than 10 Hz. The algorithm C300 then calculates RMS of
d.sup.2F/dt.sup.2 over the last N seconds (block C306), skipping
the first 0.1 second to avoid transients from the start of
retraction (e.g., motor stiction, etc.). The algorithm C300 first
looks for a negative going spike in d.sup.2F/dt.sup.2 by comparing
the last measurement to the RMS over the last N seconds (RMSN)
multiplied by the threshold Ts input by the user
(d.sup.2F/dt.sup.2<(0-TS RMSN)) (block 308). If the force is
more negative than this parameter, then a 20 s pause in retraction
(block C310) is triggered permitting force relaxation in the
tissues, and the algorithm C300 returns to the start (block C302).
If d.sup.2F/dt.sup.2 is not more negative than this parameter, then
the algorithm C300 checks for increased variability in
d.sup.2F/dt.sup.2 by comparing the RMS over the past 0.5 seconds
(RMS.sub.0.5) to the RMS over the past N seconds (RMSN) multiplied
by the threshold Tv (block C312). If RMS.sub.0.5 is greater then a
20 second pause (block C310) in retraction is triggered permitting
force relaxation in the tissues, and the algorithm C300 returns to
the start (block C302). If RMS.sub.0.5 is not greater then
retraction proceeds for another 0.1 second (block C314) and checks
again (block 306). Thus, force is checked for a negative-going
spike in d.sup.2F/dt.sup.2 and for increased variability in
d.sup.2F/de every 0.1 seconds. The force trace can be checked more
or less frequently. Other sampling frequencies can be used. The 0.1
second added tON in block C304 can be any other time interval
sufficient to avoid transients in the force trace on starting the
motor or around any other event deemed spurious to detecting tissue
trauma. The event triggered by the detection algorithm (a 20 second
pause in this case) can be any event that is appropriate to the
detected signal. For example, retraction can pause with continued
measurement of force and then retraction can resume after the slope
of the force trace becomes shallow, indicating that force
relaxation has approached a limit. Another example is to initiate
an oscillation of the retractor to accelerate force relaxation, or
to pause for a first period and then to oscillate for a second
period.
[0346] There is a fifth event for predicting imminent large breaks
in tissue during retraction. Breaks are audible. Snaps and pops
("audible events") are heard throughout a retraction. Big breaks
are louder. The large break at 46-70 sin FIG. 38B was actually a
series of repeated fractures of the tissue. This was audible as a
rapid series of loud audible events. Thus, the audible events of
tissues breaking can be used as an indicator of tissue trauma, and
audible events, including less loud events, can be used as
indicators that a larger traumatic event is about to occur. Also,
the qualities of an acoustic signal (e.g., the frequency of
occurrence of audible events) can be used as an indicator of
impending trauma. In the preceding example, the frequency of
occurrence of acoustic events becomes higher as trauma
increases.
[0347] FIG. 43 depicts how such a trace would look-two breaks
occur, one at about 55 sand another at about 255 s (marked with an
asterisk). These are preceded by audible events (marked by arrows).
These audible events might be distinguished from background noise
by sound intensity, spectral composition, or both. In another
example, the acoustic frequency (i.e., the pitch) of each acoustic
event might change; for example, the pitch of earlier events might
be higher than the pitch of later events as the tissue approaches a
large fracture.
[0348] Sound measurement can be performed by microphones or other
sound sensors placed in the air near the incision; on the
retraction device, such as with a contact microphone; or on the
patient's body, for example, with a contact microphone embedded in
a gel beneath an adhesive pad, in which the gel matches the
acoustic conduction of the body. If the sound measuring device is
placed on the patient's body, then multiple sound measuring devices
placed at distinct locations can be used to detect the position of
the fracture either by relative intensity of the sound or by
detecting time-of-arrival for triangulation of the location of the
fracture or the propagation of a locus of damage.
[0349] Acceleration can serve as a sixth event indicator. When a
large ligament snaps during retraction, the entire retractor
suddenly shakes, as will all or a portion the body of that patient
(depending on the magnitude of the tissue trauma event). With a
smooth retraction, even smaller sounds can be "felt" with
fingertips that lightly touch the retractor. Accelerometers are
ideally suited to measure these motions. Accelerometers mounted on
elements such as the body of the retractor, on the retractor
blades, and/or on the body of the patient would provide an
indication of the motions of any, some, or all of these elements.
Acceleration is thus indicative of any number of a range of events
occurring within (or to) a patient's tissues, including incipient
tissue trauma. In this way, acceleration can serve prognostic
goals. Acceleration can also provide feedback, to track the
behavior of the device itself.
[0350] An accelerometer typically measures acceleration along a
single axis. Accelerations acting directly along this axis produce
the strongest signal, while accelerations acting exactly
perpendicularly to that axis may produce little or no signal at
all. In an actual patient's body, with complex tissues and force
transmission paths, one may encounter the situation where one
cannot expect an accelerometer associated with that body to ever
register a zero output. One might mount one or more accelerometers
to a surgical instrument (for example, the body of a retractor), to
a portion of a surgical instrument (for example, one, two or a
plurality of a retractor's blades), and/or to a patient's body.
With its axis oriented at a carefully chosen angle with respect to
the local axis of retraction, a given accelerometer can provide
indications of not only an early warning of impending tissue
trauma, but also a local direction of interest with respect to
those accelerations, and a complex time series of accelerations
associated with specific tissue types or tissue behaviors. As with
the acoustic event detection above, one can use accelerometers to
detect (a) acceleration events, (b) acceleration slope events, (c)
acceleration variance events, and (d) acceleration slope variance
events.
[0351] Attaching multiple accelerometers at multiple locations
and/or angles can provide a picture, or map, in 2D, 3D, or 4D (with
time) of the forces and moments acting on the system consisting of
the body of the patient and the retractor. This picture can enable
a surgeon (or the corrective software) to know which tissue type
(or which of many tissue elements) might be involved, and/or when
and where tissue trauma will occur before the onset of major
damage. As one example, accelerations parallel to the surface of a
given retractor blade might indicate the incipient failure of
fibrous connective tissue (e.g., fascia or periosteum) oriented in
that direction, while accelerations perpendicular to the surface of
that retractor blade might indicate the
incipient failure of the rib that that retractor blade is moving.
As for corrective actions, in that example one might try to prevent
snapping connective tissue by initiating oscillating loading,
whereas one might instead respond to prevent rib breakage by
pausing the retraction.
[0352] Furthermore, accelerometers might also provide independent
confirmation of how well the actual behavior of a motorized
instrument (such as a retractor) is conforming to the commanded
behavior (whether controlled by the surgeon, the software, or some
combination of the two). This could serve as an on-the-fly
diagnostic to permit active self-correction and self-calibration.
Accommodation andre-modulation can correct performance variances
should they occur, further increasing confidence in the safe
operation of the device.
[0353] A further aspect of self-operational feedback features
(e.g., for acceleration) is that the device could adapt to the
different operating styles of surgeons, for example by enabling
detection of the operator's instrument handling patterns. For
example, an accelerometer mounted to the retractor can be used to
detect motions of the retractor arising when a surgeon
inadvertently touches the retractor (e.g., when inspecting the
incision) or purposefully handles the retractor (e.g., to adjust
the position of the retractor). Such inadvertent touches or
purposeful handling of the retractor can create transients in the
signals that resemble imminent trauma. Signals from the
accelerometer can be used to discriminate transients in the force
and/or sound traces arising from the surgeon's actions.
[0354] Using any of these events for detecting an imminent tissue
fracture or other damage, it is possible for a surgeon or an
automated system to take corrective steps to prevent the tissue
fracture. For example, upon detection of an event, retraction can
be paused, permitting force relaxation, or retraction can switch
from constant velocity retraction to an oscillating loading to use
work softening of the tissue (or related phenomena arising from
oscillating loading) to either induce an accelerated force
relaxation or to create many small tissue fractures that relieve
the stress in the tissue and prevent fracture of a major tissue
component.
[0355] It is important to recognize that the techniques described
here for detecting imminent tissue trauma by measuring force and
sound, coupled with detection of transients, can be used without
prior knowledge of a particular patient's physiology or
pathology--the signals are unique to tissue trauma, but independent
of a patient's unique characteristics. Thus, tissue trauma can be
detected whether a patient is old or young, large or small,
osteoporotic or normal. There is no requirement for determination
of a threshold force to try to avoid tissue trauma, nor is there
any need for databases of patients' characteristics and related
force-distance measurements for adjusting retraction to unique
patient parameters.
[0356] There are any number of other tissue trauma early warning
event indicators. The aforementioned examples are only intended to
teach the principle of early detection, not limit the embodiments
of sensing modality to force, sound, and acceleration.
F. Self-Balancing Retractor Blades
[0357] FIG. 44 presents an example of a Finochietto-style retractor
F2 in the prior art. It has a fixed retraction element F6 attached
to rack of a rack-and-pinion drive Fl 0 that is manually driven by
rotation of the drive handle F12. A moveable retraction element F8
is attached to the drive of the rack-and-pinion drive F1O Each of
the retraction elements F6, F8 has a single retractor blade F4 that
engages the tissue to be retracted.
[0358] The forces under the retractor blades F4 can be large.
Furthermore, an edge of a retractor blade F4 can become a
point-load if the retractor blade F4 is not well-seated or if the
retractor blade F4 contacts a curved surface, such as a rib. If a
retractor blade F4 becomes a point load, then the stress in the
tissue at the point of loading can become extreme. Broken ribs are
common using these types of devices.
[0359] Such maladjustments of a blade can be reduced if several
blades are used to engage the edge of an incision. FIG. 45 shows a
retractor 300 in the prior art from the lab of Greg Buckner
(Buckner and Bolotin 2006; Bolotin, Buckner et al. 2007). This
retractor has six retractor blades 200 attached to a common frame
700. Each retractor blade 200 has an intermediate member 220 that
connects the retractor blade 200 to an actuator 300. Thus, each
retractor blade 200 has its own actuator 300. FIG. 45A is a diagram
of the retractor 300. FIG. 45B is a photograph of the retractor 300
being used in a thoracotomy in a sheep, demonstrating how the
retractor blades 200 engage the margins of the incision. The use of
multiple retractor blades 200 along the margin of the incision
distributes the retraction forces, reducing the force on any single
retractor blade 200. However, the load on any single retractor
blade 200 is determined by how hard it pulls on the incision as set
by the actuator 300 of that particular retractor blade 200.
Adjusting the forces to be equivalent to one another, or to have
any other desired distribution of forces, requires individual
adjustment of all the actuators 300 which must be made by an
operator (which would be slow and irregular) or by an automated
system combining force measurement, motorized actuators, and a
control system (which might be expensive).
[0360] Discussion of the next section requires review of a piece of
very old prior art, related to the harnesses of draught horses that
pull wagons. A "swingletree" is a pivoted, suspended crossbar to
which the two traces of a horse's harness are attached when it
pulls a wagon. FIG. 46 shows a top view of a swingletree F94
attached to wagon F97 by first harness component F104. Swingletree
F94 attaches to harness component F104 at pivot F98. Two traces F96
of the harness extend from swingletree F94 to the collar F92
against which horse F90 pulls, exerting force F106 met by reaction
force F107 and creating force F108 on the pivot F98 and force F102
on the wagon F97. If due to uneven motion of the horse, the force
on traces F96 become unbalanced, then the moment about pivot F98
causes swingletree F94 to rotate until the forces on the traces F96
become balanced.
[0361] Every horse F90 attached to a wagon F97 pulls against a
swingletree F94. When more than one horse pulls a wagon, multiple
swingletrees are tiered, as shown in FIG. 47. Two horses F1110 and
F112 pull a wagon F124. Each horse F110 and F112 pulls on its own
(child) swingletree F120, and the two swingletrees F120 are
attached to a third (parent) swingletree F122 that is also known as
a "doubletree". The entire structure connecting the swingletrees
F120 and F122 is a tensile one, and rotation of swingletrees F120
and F122 balances the forces on each swingletree. Ultimately, the
pivot F130 ensures that only a tensile force is applied to wagon
F124, and rotation of the swingletrees F120 and F122 isolates all
unbalanced forces from wagon F124.
[0362] FIGS. 48A and 48B show another retractor F150 in the prior
art. This is the Skyhook from Rultract (www.rultract.net, U.S. Pat.
No. 4,622,955). The retractor F150 is a hoist, suspended above a
patient F163, with two retraction rakes F160, F164, F166 that
engage a bisected sternum F162 at two locations, and the retraction
rakes F160, F164, F166 attach to the opposite ends of a swingletree
F156, F170. A cable F154, F168 attaches to the mid-point of the
swingletree F156, F170, and the swingletree F156, F170 is free to
pivot about this attachment. As seen in FIG. 48B, when the winch
F158 pulls the swingletree F156, F170 upward, if one of the
retraction rakes, such as F164, engages the margin of the incision
F162 first, then that retraction rake F164 is pulled downward,
which pulls the opposite retraction rake F166 upward until both
rakes F164 and F166 engage the margin of the incision F162, where
the swingletree F170 has rotated with the right retraction rake
F166 raised above the left retraction rake F164. Force exerted by
the cable F168, through the swingletree F170, and then through the
retraction rakes F164 and F166 pulls the bisected sternum F162
upward to provide surgical access for the surgeon. The swingletree
F170 here ensures that the forces on the two retractor rakes F164
and F166 remain equal-if the force on one retraction rake, for
example retraction rake F164, is larger, then the other retraction
rake F166 is pulled upward until the forces on the two retraction
rakes F164 and F166 are balanced. More specifically, the
swingletree F160, F170 rotates whenever the moment about the
pivoting attachment to the cable F154, F168 become unbalanced. This
occurs automatically. One drawback of the retractor F150 is that it
requires a large derrick-like arm F152 that is bolted to an
operating table F153 that suspends the winch F158 over the patient
F163, or some similar superstructure over the operating table F153.
Such structures can obstruct the surgical field, making access
difficult from some angles, and present the risk of dropping the
requisite fasteners into the patient's open chest cavity.
[0363] A means for automatically adjusting the force exerted by
each retractor element without the large, table-mounted hardware of
the retractor F150 and with fewer actuators than the device of
FIGS. 45A & 45B is desirable.
[0364] FIGS. 49A and 49B illustrate one embodiment that balances
the forces on multiple retractor blades without table-mounted
hardware and with fewer actuators. This is a retractor F172 that
uses a mechanical system for balancing forces on the opposing arms
of a Finochietto-style retractor in the prior art (see FIG. 44).
Four retractor blades F184 engage the margins F202 of the incision
to be retracted and create a surgical aperture F200. Retraction is
manually driven by rotation of the drive handle F174 acting on
rack-and-pinion drive F175 which moves along rack F176. There is a
pair of blades F184 (also labeled F196 and F198 in view F190 in
FIGS. 49B.1 and 49B.2, respectively) on each retraction element
F178 and F180 of the retractor F172. A first balancing assembly
F186 is comprised of two retractor blades F184 in each pair which
are attached to a balance bar F188, and the first balancing
assembly F186 on the fixed retraction element F178 opposes a second
balancing assembly F185 on the moveable retraction element F180.
Each balance bar F188 is attached to its respective retraction
element F178 or F180 by a pivoting mount F187 or F189 so that the
balance bar F188 is able to rotate in the plane of the page in FIG.
49A, but rotation of the balancing bar F188 in the two planes
perpendicular to the plane of FIG. 49A is not permitted.
Prohibition of rotation in those other two planes permits the use
of rigid mounts to retractor blades, retraction hooks, or retractor
rakes. In FIG. 49B.1, a balance bar F193 will rotate F195 about a
pivot point F194, and within the plane of the page, to balance
forces F204 and F206 on the two retractor blades F196 and F198
attached to the balance bar F193, and will stop rotating F195 when
the two forces F204 and F206 are balanced. Additionally, should the
two forces F204 and F206 again become unbalanced as retraction F212
proceeds, the balance bar F193 will, again, automatically rotate
F195 the retractor blades F196 and F198 to balance the forces F204
and F206 on the blades F196 and F198. In FIG. 49B.2 depicts a
subsequent state of view F190 showing a balanced state for a pair
of forces F208 and F210 during retraction F214, such that F208 and
F210 have equalized due to the accommodation via rotation F218 of
balance bar F216 about pivot point F217.
[0365] Referring now to FIG. 50A through SOC, FIG. 50A shows how a
balance bar F226, F236 and F246 can be adjusted such that the
balance bar F226, F236 or F246 maintains an approximately constant
ratio of forces F232, F242, F252 versus F234, F244, F254 between
two retractor blades (not shown) located at the ends of the balance
bar F226, F236 or F246. As shown in FIG. 50A balance bar F226
rotates, not due to an imbalance of the forces F232 and F234 on the
retractor blades, but due to an imbalance of moment MF227 about the
pivot point F228. Thus, if the length L1 of a first side of balance
bar F226 is longer than the length L2 of a second side of balance
bar F226, then the force F, F232 on that first side will be smaller
than the force F.sub.2 F234 on the second side when the moment
MF227 is zero. Any ratio of forces can thus be accommodated.
Additionally, the geometry of the balance bar F226 determines a
"righting moment", a moment that returns the position of the
balance bar F226 to neutral when displaced from neutral, and
thereby makes the balance bar F226 "self righting." As shown in
FIG. SOB, the righting moment is determined by the angle D
(D=D.sub.1+O2) formed by lines L.sub.1 and L2 and by the length of
lines L and L2. For example, the moment generated by F2L2sin[12 is
maximal when L2 is a long as possible and O2 equals 90.degree., and
the moment generated by F.sub.1L.sub.1sinDu is minimal when O.sub.1
equals 0.degree. regardless of the length of L.sub.1; therefore,
the balance bar F236 will be maximally self-aligning when D equals
900 (see FIG. 50C). However, if a 900 rotation is not anticipated
when the balance bar is used, then D D D D D D O.degree.-2De
(De=the maximum angle of rotation in use) provides the largest
righting moment.
[0366] As shown in FIG. 51, more than two retractor blades F270,
shown as F270B, F270 B2, F270 B.sub.3 and F270 B.sub.4, located on
a retraction element F263, to be retracted in the direction F278,
and another four retractor blades, shown as F272 B.sub.1', F272
B2', F272 B/, and F272 B.sub.4', located on the retraction element
F265 and to be retracted in the opposite direction F280 can be
placed onto each retraction element F263, 265 of a retractor F260.
This is accomplished by tiering balance bars F262, F266 and F267
onto which retraction blades F270 B.sub.1 to B.sub.4 are mounted
and also tiering balance bars F264, F268 and F269 onto which
retractor blades F272 B.sub.1' to B.sub.4' are mounted. Multiple
tiers of balance bars are possible.
[0367] FIG. 52 shows how retractor blade numbers that are not
multiples of 2 can be arranged so that the forces and moments still
balance one another. As shown in FIG. 52 the force (not shown)
generated by a retraction F300 on a blade F298 B.sub.3 equals the
combined forces (not shown) on two more blades F288 B.sub.1 and
F294 B2. Similarly to that shown in FIG. 51, multiple tiers of
balance bars are possible, including those creating uneven numbers
of retractor blades. Again, all balance bar elements will stop
rotating when the moments about their respective pivot points
equalize.
[0368] Blades can be mounted to balance bars such that they are
fixed or pivoting. As shown in FIGS. 53 and 54, balance bars can in
some instances also be mounted by a tensile element such as a
cable, chain, or wire, permitting rotation out of the plane of the
page in FIGS. 53 and 54, similar to a swingletree. FIG. 53 shows in
more detail a retractor F302 with retraction elements F306 and
F308, a rack-and-pinion drive F305 with a drive handle F304, and
four retractor blades F316 associated with two opposing balance
bars F310. The balance bars F310 are connected to the retraction
elements F306 and F308 by tensile elements, cables F312 and F314.
Cables F312 and F314 permit easy, generous reorientation of the
retractor blades F316 to forces and accommodation of moments by the
balance bars F310 while still transmitting the forces arising out
of the motion F318 of the movable retraction element F308. FIG. 54
shows how multiple balance bars F338, F330, F340 can be tiered
(similar to FIG. 51) by the use of chains F332, F334, and F336
attached by pivoting joint F324 on balance bar F338 and pivoting
joints F328 on balance bars F330 and F340.
[0369] FIGS. 55A through 55C show a top view, a side view, and a
front view, respectively, of another embodiment in which an entire
retractor element F348 is able to rotate around the axis of
retraction F351; additionally, the retractor blades F362 are shaped
like hooks that engage a rib F364 to avoid damage to a
neurovascular bundle (not shown), as described more fully in
Section H. In FIG. 55A, the base element F350 of the retractor
element F348 is attached by a rotational joint F352 that allows the
entire retractor element F349 to rotate out of the plane of the
page in the top view (FIG. 55A) and within the plane of the page in
the front view (FIG. 55C). Thus, rotational joint F352 permits the
base element F350 of the retraction element F349 to rotate within a
plane perpendicular to the axis of retraction. Base element F350
attaches to a first balance bar F354 by rotatable joint F358, and
first balance bar F354 attaches to second balance bars F356 by
rotatable joints F358. Two (2) hook-shaped retractor blades F364
descend from each second balance bar F356. Rotational joints 352,
or their equivalents, can be placed at every rotatable joint F358
providing tremendous freedom of movement for the balance bars F354
and F356 and the hook-shaped retractor blades F362.
[0370] FIGS. 56A through 56C show a top view, a side view, and a
front view, respectively, of an embodiment similar to that shown in
FIGS. 55A through 55C, but an articulation F400 has been added to
balance bar F354 allowing it to bend to conform the balance bar
F354 to a patient's rib F364 that curves in the plane perpendicular
to the plane of the page as seen in the top view (FIG. 56A). Again,
note that a cable, chain, or wire, as depicted in FIG. F54, could
also permit rotation of the type shown at rotational joint
F352.
[0371] FIG. 57 shows a Finochietto-style retractor F430, similar to
retractor F172 shown in FIGS. 49A through 49B, with an opposing
pair of swingletrees F437 and F439. Retraction elements F436 and
F438 have retractor arms F433 with articulations F434 that allow
the retractor arms F433 to conform to the curve of a patient's
body. These articulations F434 could be passive, starting out with
the retractor arms F433 straight and then conforming to the body
when encountering the body, or the articulations F434 could be
preset by the surgeon and rigidly fixed in a patient-body conformal
shape beforehand, or they could be self-controlled via sensor
feedback. The articulations F434 might be formed as hinges, with
two discrete sections interdigitating as shown in the FIG. 574, or
the articulations F434 might be formed as elastomeric regions that
bend smoothly from one section of a retraction element to another.
Another embodiment might possess retraction elements F436, F438
which are continuously, smoothly flexible (along their length) in
one plane, while rigid in the others.
[0372] FIG. 58 shows another embodiment of a retraction element
F442 that permits more complex force distribution. Balance bars
F443 and F445 form a second (child) tier F449 to a first (parent)
tier F447, connecting at rotatable joint F446. Each balance bar
F443, F448 has two retraction blades F448 attached by rotatable
mounts F451. Balance bars F443 and F445 are overlapped at F450,
presenting opportunities for generating a broader range of moment
arms to distribute the pattern of forces along the margin of the
incision. A broad range of overlap, bar length, and pivot position
is possible; preferred embodiments arrange bar lengths, amount of
overlap, and pivot positions so that all moments equalize, but this
need not be the case. Surgical situations may arise such that a
clinician wishes to apply forces irregularly, for example if one is
forced to simultaneously retract both exposed bone and soft muscle
or adipose tissue in the same incision, or for example if a surgeon
wishes to create a surgical aperture with purposefully nonparallel
incision margins. Note also that besides varying the foregoing
items in a surgical instrument design, the number of hierarchical
levels is not restricted. It may be advantageous to provide many
`child` levels of balance bars below the `parent` level, forming a
balance bar cascade of arbitrary fineness, for example to ensure
that dozens of tiny retraction hooks engage a patient's tissues,
providing for nearly continuous support across the tissue face.
Combining all four design variables permits the design of
retractors of arbitrary complexity that apply appropriate
arrangements of forces in useful directions to a variety of tissues
and anatomical structures without incurring tissue trauma.
[0373] FIGS. 59A through 59E show another embodiment of a
retraction element that achieves automatic balancing of loads.
Rather than using a swingletree, this retractor uses a cable F466
to transmit loads between retractor blades, posts, or hooks F468
that are mounted onto retraction arm units F462 by a rotational
mount F460 formed by pin F470 which attaches retraction hook F468
to retraction arm unit F462. FIG. 59A shows a side view showing one
retraction hook F468 attached to a retraction arm unit F462 by a
rotatable mount F460. The retraction hook F468 engages a rib F456,
directly against that bone, such as in a thoracotomy. The cable
F466 attaches to the retraction hook F468 by passing through a hole
F480 in the shaft F469 of the retraction hook F468. FIG. 59B shows
a front view, with three retraction hooks F468 attaching to the
retraction arm unit F462. The retraction arm unit F462 has two
articulations F474, permitting the retractor arm tmits F462 to
independently align to the curvature of the rib. Optionally, the
retractor arms can be solid, without articulations F474. Referring
to FIG. 59B, the cable F466 attaches at one end to a retraction
element F462 and then courses through the holes F480 in the
retraction hook shafts F469 and over pins F464 in the retraction
arm units F462; finally, cable F466 attaches at its other end to a
capstan F478 used to adjust the tension of the cable F466, and
thereby adjust the magnitude of the swinging of the retraction
hooks F468. FIG. 59C shows a top view, illustrating how the cable
F466 travels from an attachment F482 at one end, then zig-zags left
to right, back and forth as it passes from holes F480 in the shafts
F469 of the retraction hooks F468 to pins F464 inside recessed
holes in the retraction arm units and finally to a capstan F478.
Thus, as illustrated in FIG. 59D, when a first retraction hook F468
is pushed (by the tissues at the margin of the incision) toward the
left, it tensions the cable F466, which then pulls a neighboring
retraction hook (F468') to the right. This repositioning of the
retraction hooks F468 and F468' will continue until the force on
both retraction hooks equalizes.
[0374] Again, changes in the position of the through hole F480 in
the shaft of the retraction hook F468 and F468' will control the
ratio of forces between those retraction hooks. FIG. 59E shows how
the articulations F474 between retraction arm units F462 permit the
retraction arm units F462 to conform to the curvature of the
patient's body.
[0375] FIGS. 60A and 60B show a physical model of a retractor F540
of the type described in FIG. 59A through 59E. FIG. 60A shows a top
view of the retractor F540, and FIG. 60B shows an oblique side view
of the retractor F540, showing the retraction hooks F558 (similar
to F468) and cables F556 (similar to F466). Paired retraction
elements F544 are attached to and ride along a dual-thrust lead
screw F546. Rotation of the dual-thrust lead screw F546 with
respect to the retraction elements F544 causes the retraction
elements F544 to move F548 apart for retraction or back together
for closure. The retraction elements F544 have articulations F552,
like articulations F464 in FIGS. 59A-59E. Retraction hooks F558 are
attached to the retraction elements F544 in the same manner as
described in FIG. 59. The retraction hooks F558 are rotatable about
their long axes, such that prior to insertion into an incision to
create a surgical aperture, a surgeon can first align the
hook-shaped tips of the retraction hooks F558 all pointing parallel
to the direction of the incision (and so parallel to the margins of
the incision, making that part of the retractor F540 that actually
descends into the patient as thin as possible) for easy insertion
into the incision and then, secondarily, the surgeon can rotate the
retraction hooks F558 such that the hook shapes swing out and under
the ribs adjacent to the retraction elements F544 (on the left and
right side, respectively) to engage the ribs for retraction.
Margins F555 of the two retraction elements F544 can be shaped such
that the retraction hooks F558 on one retraction element F544
interdigitate with the retraction hooks F558 of the opposing
retraction element F544, decreasing the separation of the axes of
the retraction hooks F558 to zero when they are inserted into the
incision. FIG. F60B shows the retraction hooks F558 aligned in this
instance parallel to the direction of the incision; the retraction
elements F544 here have been somewhat differentially rotated about
the dual-thrust lead screw F546 to make it clear how the shape of
the margin F555 of the retraction elements F544 can be sinuous,
permitting the interdigitation of the left and right retraction
elements F544.
[0376] FIG. 61 shows another embodiment of a retractor F560 that
achieves automatic balancing of loads. Multiple retractor blades
F566 are mounted onto hydraulic cylinders F573 having pistons F572
that move in response to pressure F567 in the hydraulic cylinder
F573, and the hydraulic cylinders F573 are fluidically F569
connected by hydraulic interconnects F574 and arrayed in opposing
gangs 570 of hydraulic cyliners F573. The gangs F570 of hydraulic
cylinders F573 are positioned on a fixed retraction element F562
and a moveable retraction element F564 of a Finochietto-style
retractor driven by a handle F568. When, for example during
retraction, the tissue resistance force on an arbitrary first
retractor blade F566 draws out the first retractor blade F566 such
that the first hydraulic piston F572 to which that the first
retractor blade F566 is attached is also pulled a portion of the
length of hydraulic piston F572 out of the first hydraulic cylinder
F573, then the pressure F567 inside the first hydraulic cylinder
F573 decreases. This decrease in pressure F567, communicated to the
other hydraulic cylinders F573 via the hydraulic interconnects
F574, causes internal fluid F569 to flow into this first hydraulic
cylinder F573 from the other hydraulic cylinders F573. Flow of the
internal fluid F569 out of the other hydraulic cylinders F573
decreases their internal pressures F567 consequently pulling the
other hydraulic pistons F572 inward, so causing the other retractor
blades F566 attached to the other hydraulic pistons F572 to move
F576 in a direction opposite that of the first retractor blade
F566. As with the embodiments above, the ratios of forces between
all the retractor blades F566 can be designed to be any ratio
desired, for example by the use of hydraulic cylinders F573 with
different radii. In another embodiment, the hydraulic cylinders
F573 can be a single hollow fluid-filled housing with four pistons
(or other number of pistons) emitting from the housing, with the
housing acting as a fluidic plenum keeping all four pistons in
hydraulic communication. The hydraulic fluid in these systems can
be oil, sterile water, sterile saline, or a gas, such as air. Air
further provides compressibility which acts like a "spring" in such
a system, enabling compliance appropriate when loading tissues, for
example.
[0377] FIG. 62 shows another embodiment of a retractor F580 that
achieves automatic balancing of loads with hydraulics. Similar to
the cabled device depicted in FIGS. 59A through 59E, retraction
hooks F584 and F586 are attached to retraction elements F582 by
rotatable mounts F588; however, now the cables are replaced by a
series of hydraulic cylinders F590 that compress or elongate (i.e.,
change total length) as the retraction hooks F584 and F586 rotate
about the rotatable mount F588. The hydraulic cylinders F590 are
fluidically connected at fluidic connection F599, so as one
hydraulic cylinder F590 is elongated, for example, it pulls
hydraulic fluid F591 from the other hydraulic cylinders F590,
causing them to shorten. Thus, as shown in FIG. 62, as a first
retraction hook F584 is pushed to the left (movement F594), causing
this first retraction hook F584 to rotate clockwise about the
rotatable mount F588, the hydraulic cylinder F590 of retraction
hook F584 elongates, making the other hydraulic cylinders F590
(such as that associated with the second retraction hook F586)
shorten, thereby rotating second retraction hook F586
counter-clockwise about the rotatable joint F588, making second
retraction hook F586 move to the right (movement F592).
Alternatively, the hydraulic elements F590 and F599 can be arranged
to be compressed under load instead of pulled, driving fluid F591
out of the hydraulic cylinder F590 of the first (engaging)
retraction hook F584 and into the hydraulic cylinder F590 of the
second (reacting) retraction hook F586.
[0378] FIGS. 63A through 63E show another embodiment or a
retraction element F608 with retraction posts F602 that compensate
for one another's motion via retrograde action. Fenestrated bars
F604 link retraction posts F602, and motion of one retraction post
F602 causes the other retraction posts F602 to adjust via a
mechanical linkage through fenestrated bars F604. FIG. 63A shows a
model with the fenestrated bars F604 mounted on a fulcrum F606 and
the retraction posts F602 passing through the fenestrated bars F604
via holes F605, with the counteracting offsets of the retraction
posts F602 being evident. FIG. 63B shows a top view and FIG. 63C
shows a side view of a retraction element F608. Each fenestrated
bar F604 in this example possesses two holes F605 through which
pass two retraction posts F602. Each fenestrated bar F604 then
further possesses one more hole F631 admitting a fulcrum pin F630,
forming the fulcrum F606 upon which and about which the fenestrated
bar F604 is free to rotate. The fenestrated bar F604 resides in
this example close to the base of the retraction arm F612, to which
each retraction post F602 is connected via a hinge F632 which
allows each retraction post F602 to swing back and forth along the
axis of retraction F639. FIG. 63D shows the action for one
retraction element F608. Consider the middle retraction post F602
and its two fenestrated bars F602. As a the middle retraction post
F602 gets pushed backwards by the impinging tissue, the middle
retraction post F602 moves backwards, and this motion is
transmitted as a moment by both fenestrated bars F604 around the
fulcrum F606 to the top and bottom retraction posts F602, pushing
that the top and bottom retraction post F602 forward to meet the
oncoming tissue. As with some of the other embodiments disclosed
above, the motion of the retraction posts F602 ceases when the
moments equalize. FIG. 63E shows the counter motion of that shown
in FIG. 63D. This embodiment possesses two fenestrated bars F604
that together link the motions (and so the countermotions) of three
retraction posts F602. Note that one may design the fenestrated bar
system with an arbitrary number n of fenestrated bars linking n+1
retraction posts. Note also that one may combine fenestrated bars
of arbitrary lengths and proportions so creating useful variations
of motion of the retraction posts without departing from the intent
of the present invention.
[0379] FIGS. 64 through 66B show still another embodiment of a
retraction element of the current invention, this time providing
swingletrees with the ability to automatically, dynamically and
continuously adjust the position of their pivots to accommodate
changing loads. In all FIGS. 64 through 66B the direction of
retraction would be "up" towards the top of the page, and the
patient's tissues would thus react by pulling "down" towards the
bottom of the page. The retractor blades shown in FIGS. 64 through
66B thus engage an incision along the bottom of the page.
[0380] FIG. 64A shows retraction element F700 having a rectractor
arm F702 that is used to pull up in the direction of retraction
F701 F722. A two-tiered assembly of swingletrees, comprised of
first swingletree F704 ("parent swingletree") and second
swingletrees F706 ("child swingletree") hold four (4) retractor
blades F708. First singletree F704 attaches to retractor arm F702
via pivot F710, here shown as a sheave. Second swingletrees F706
attach to first swingletree F704 also via pivot F710, here shown as
a sheave. Retractor arms F708 attach to second swingletrees F706
via a pivot point F712, here shown as a rotating mount formed by a
pin and a bushing. Swingletrees F704 and F706 still pivot within
the plane of the page about a pivot F710 that acts as a fulcrum,
shown here as a freely rotating sheave.
[0381] FIGS. 65A through 65C show side views of two different
embodiments of retraction element F700. FIGS. 65A and 65B show side
views of the retraction assembly F700 shown in FIG. 64. FIG. 65C
shows another embodiment of retractor assembly F700 that captures
first swingletree F704 and second swingletree F706 such that the
assembly is held together. The sheave F720 at pivot F710 can be a
bearing-mounted roller. As shown in FIG. 65B, the sheave F720
includes a provision (such as a groove F722 or channel around its
rim) for cupping, nestling, or riding along and otherwise retaining
its association with that edge F724 of each swingletree F704, F706
that is closest to the incision. The first and second swingletrees
F704 and F706, respectively, includes a provision so that it mates
with the sheave F720. As shown in FIG. 25B, the lower edge F724 of
swingletrees F704, F706 can be convexly radiused and otherwise
shaped to accept the concavely shaped groove F722 of the sheave
F720. Given this arrangement, the lower edge F724 of swingletrees
F704, F706 ride in the groove F722 of the sheave F720, such that
the loading by the patient's tissues retraction actually seats the
swingletrees F704, F706 more securely in the sheave F720.
[0382] FIG. 25C shows another embodiment of the retractor assembly
F700, here labeled as retractor assembly F730. To avoid
swingletrees F704, F706 disengaging from sheaves F722, first
swingletree F704 is mated with another swingletee F732, creating a
stacked assembly with two sheaves F722 connected to each other by a
pin F732 through retractor arm F702. First swingletrees F704, F732
are thus captured by retractor arm F702, and second swingletree
F706 is thus captured by doubled first swingletrees F704, F732.
Another means of capturing each swingletree F704, F706 is to have
sheave F720 ride in a restrictive slot formed within the child
swingletree bar, instead of riding along the lower edge of the
swingletree.
[0383] A "child" swingletree (e.g., second swingletree F706) can
serve as the "parent" of other swingletrees (in this case, F676 and
F677) lower down in the hierarchy, creating as many levels as
desired. Properly sized and assembled, such a network of
swingletrees automatically assures so that no excess or imbalance
of forces can remain.
[0384] In this way, any excess force applied against the tissue of
the patient is reduced. [00324]One problem with retractor blades
and the like is their tendency to apply not only forces directly
against the tissue of the patient, but to shear along (or roughly
parallel to) the raw surface of the incision. As a retraction
proceeds, the relative motion or loading of the retractor blades
may induce sliding along the edge of the margin ofthe incision (or
an attempt by one or more retraction elements to do so), shearing
the tissue in that plane (or tearing it outright).
[0385] FIGS. 66A and 66B show another embodiment that uses
distributed curvature of the freely riding swingletrees to limit
this shearing motion of the retractor blades. FIG. 66A shows a
retraction assembly F740 having swingletrees with tightly curved
anns that make retraction assembly F740 more prone to shearing of
the retractor blades, and FIG. 66B shows a retraction assembly F760
having swingletrees with more gently curved arms that that make
retraction assembly F760 less prone to shearing of the retractor
blades. The local curvature of the swingletree surface (riding in
the parent sheave) influences the magnitude of the shear applied by
rectractor blades F712 along the surface of the incision (i.e., the
behavior of the swingletree hierarchy is a function of the
curvature of the swingletrees comprising it). Consider FIG. 66A,
swingletrees F742 and F744 are shaped with a substantially high
curvature near the center of the swingletree, and lower curvature
near their tips; thus, sheaves F720 experience strong centering
forces F748 and remain more tightly centered under load, behaving
much (but not all) of the time as if the pivots F710 formed by
sheaves F720 were simply drilled through the bodies of the
swingletrees. Under this circumstance shear is more likely to
develop along the surface of the incision. Consider now FIG. 66B
with swingletrees F762, F764 shaped with a much gentler
distribution of curvature along the swingletree bar, then the
centering forces F768 are smaller. Shear is instead relieved as the
pivots F710 of the swingletrees F762, F764 can more easily shift
laterally to suit owing to the smaller centering forces F768.
Ideally, shear applied to the margin of the incision is minimal and
the pivots F710 supporting a given swingletree F762, F764 remain
substantially near the center of its respective swingletree F762,
F764, thereby allowing the swingletree to rotate about the axis of
the pivot F710, and within the plane of the page, to accommodate
irregular loading as before. The gently curved swingletrees F762,
F764 thus permit simultaneous accommodation of rotation and
sliding, thereby eliminating both excessive forces and shear.
[0386] Note that the intersection between the parent sheave and the
child swingletree can be formed of two smooth surfaces, or it could
be formed like a rack-and-pinion, where the parent sheave is a
toothed like a pinion gear and the mating lower surface of the
child swingletree bar is a toothed rack. Given this, one could
further arrange for the active sensing and actuator control of the
sheave rotation such that the position of the child is influenced
by the active rotation (or clutching) of the sheave. This example
admits active modulation of the play of forces and moments through
a swingletree cascade. In some instances it may prove advantageous
to apply shear on purpose, or to imbalance the forces applied to
the patient's tissues, according to the needs of the surgeon.
G. Reducing Inappropriate Forces
G.1 Forces Exerted by Retractors on Tissues
[0387] When a surgeon performs a thoracotomy, she must deform a
patient's body wall to move the apposed ribs aside far enough to
permit her hands to access the thoracic cavity (see FIG. 67).
Current medical practice dictates that a surgeon (1) makes an
incision between and parallel to two apposed, adjacent ribs; (2)
simultaneously inserts the opposing blades of a rib spreader, or
"retractor", into the incision; and (3) turns the crank to force
open the opposing blades, and the ribs, creating a hole. The hole
or surgical "aperture" is typically about 10 centimeters across,
and can range from 5 em to 20 em. Modem retractors are essentially
rigid metal devices sporting hand-cranked jack elements. Today's
spreaders, such as Finochietto-style retractors (see FIGS. 2 and
68A) are typically rack-and-pinion devices that, while constructed
of polished stainless steel, operate on simple mechanical
principles similar to those of 2,000-year-old bronze medical
instruments found in ancient Greece (a vaginal speculum, see FIG.
68B), that is, a hand-cranked jack driving projecting blades. The
retractor shown in FIGS. 2 and 68A are widely used; this retractor
uses a lockable rack-and-pinion crank, as first disclosed by
Finochietto in 1936 and published in 1941 (Bonfils-Roberts 1972).
The principle remains the same as the ancient ones: equip a frame,
otherwise rigid in all directions and along all axes, with the
ability to expand along a single axis to simply overpower the
tissues to force access to the inside of the patient's body. Thus,
referring now to FIG. 69, the force required for opening is
considered to be simply opposing forces F.sub.1 G8 and F.sub.2 G10,
applied at two points P.sub.1 G12 and P.sub.2 G14 lying on a single
line of action. The only accommodations for more complex forces
provided by the prior art are curved retractor blades, providing
for example, non-point loading such as on a Cooley retractor G16
(FIG. 70A), and swiveling retractor blades such as on older
retractors that are no longer used (e.g. the retractors of
Sauerbruch G18 (FIG. 70B), De Quervain G20 (FIG. 70C), and Meyer
G22 (FIG. 70D). Archeological museums and current medical supply
catalogs visibly demonstrate that this one-dimensional thinking has
underlain retraction device design for millennia.
[0388] Retractors work--they do force open bodies, but their design
does not take into account the complex loading regime imposed on
(and, in reaction, by) the patient's body. The result is that
today's patient's tissues are bearing substantial loads that are
not directly related to, or required for, opening; therefore, these
retractors are causing unnecessary tissue trauma.
[0389] The inventors have measured forces during thoracotomy and
observed for the first time that the actual forces of retraction
are not the simple, one-dimensional case depicted in FIG. 69. It
can now be appreciated that a complex set of forces and torques
interact on the retractor, and thus on the patient's tissues. There
are two lines of evidence for this claim. First, the force on a
retractor (see FIG. 71, discussed below) is usually sufficient to
lift the body of the retractor off the patient's body, such as in
FIG. 67. Second, our measurements reveal that the forces acting on
opposing retractor arms are not the same. FIG. 72 shows our new
data that were collected with the retractor shown in FIG. 12, which
is fitted with a computer-controlled stepper motor B8 to provide
smooth motion and with a linear potentiometer B16 to measure the
distance of separation of the retractor blades B20 and with strain
gauges on the retractor blades B20 to measure the forces on each of
the two retractor blades B20. This retractor was used to perform
thoracotomies on the carcass of a pig. In the retraction shown in
FIG. 72, retraction occurred over 6 minutes, starting at 10
seconds, with a two-minute pause in retraction from 70 seconds to
190 seconds. The difference in the forces G64, G66 measured on the
two retractor blades is maximal at the end of retraction (at
time=480 seconds, 19.5 kg versus 16.0 kg, a difference of about
20%). These force measurements demonstrate that retractors in the
real world do not behave like perfect force diagrams out of a
physics book as shown in FIG. 69, with two endpoints of zero extent
(and equal force) connected by a one-dimensional line.
[0390] Applying pure tension or compression with today's retractors
seems impossible. In light of the observations and measurements
presented in FIGS. 71 and 72, it is difficult to imagine that one
could ever see equal forces acting on the two blades of a
conventional retractor placed inside a real patient.
[0391] Why is this so? Refer to FIG. 71. First, retractors such as
retractor G24 possess significant mass that is distributed
unevenly, and they have blades G33 and G31 with non-zero dimensions
and corners. Second, the patient's body is a sculpturally and
structurally complex composite of heterogeneous biomaterials. Every
structure inside a patient (example e.g., ribs G26 and G28) is
anisotropic and almost nothing behaves linearly. When the blades
G31 and G33 of the retractor G24 engage the two sides of an
incision, the body forcefully opposes motion of the blades G31 and
G33. The patient's tissues (e.g., ribs G26 and G28) grew and
developed alongside each other and the forces they generate tend to
restore their apposed relationships. While the retractor G24 drives
its retractor blades G31, G33 apart in a straight line, such as
displacement G32 and G30, the there are numerous forces G36, G38,
G40, G42, G52 G56 and G58 and torques G27, G34, G44, G46, G48, G50,
G54 and G60 acting on the retractor blades G31 and G32 that arise
from the deformations of the heterogeneous, three-dimensionally
complex tissues surrounding the incision. Consequently, these
forces are similarly three-dimensional and complex.
[0392] In the act of forcing open a living body with a conventional
retractor G24, first one corner of one of the inserted retractor
blades G31 will strike some part of a rib G26 and settle onto that
rib G26 and the intervening muscle tissue in an irregular fashion.
Once that happens, and since the retractor G24 is a rigid object,
the retractor G24 will react to the first contact, shifting
position, until the other retractor blade G33 encounters and
settles somewhere onto its own opposing rib G28 and muscle. The
retractor G24 then reacts and shifts again, with the blades G31,
G33 sliding along and shearing muscle against bone, back and forth
in concert, as the surgeon applies torque to the retractor handle
G35 (and so the entire retractor) as the patient's body forcefully
opposes motion of the retractor blades G31, G33. All the while, the
patient's body deforms unevenly under the loads imposed by the
retractor G24. The structures of the patient's body are deforming,
which affects re-seating of the retractor blades G31, G33, which
affects the deformation of the body, and so forth. All elements are
shifting at once, but not evenly (i.e., not rectilinearly). The
retractor G24 is essentially a rigid object; at any time, there is
little or no provision for the complex mechanical behaviors that
are the hallmark of living tissue. Because of this, and crucially,
the retractor blades G31 and G33 apply uneven forces to the body
throughout spreading, and the forces are uneven when the surgeon
achieves the required opening.
[0393] The apparent intention of the designers of conventional
retractors was to apply large forces along a single line of action
(the "retraction axis"). However, they do not accomplish this
because they do not consider the response of the patient's body.
The forces on the retractor are those imposed by the reaction of
the patient's body to the displacement of its tissues, and the
patient's body does not respond along a single line of action-it
generates complex, three-dimensional forces in response to
deformation. Furthermore, these forces change as deformation
proceeds while the retractor remains in contact with the patient's
body tissues. The retractor, in return, opposes these forces by
moving (e.g. lifting off of the patient's body) or by accumulating
stresses in the retractor. Consequently, the patient's tissues bear
substantial stresses beyond those required for opening, leading to
tissue trauma (e.g., broken ribs) that, otherwise, should be
avoidable.
[0394] Clearly, minimizing undue stresses during a thoracotomy or
other surgical procedure would be beneficial to the patient,
reducing tissue trauma to the barest minimum required to generate
an adequate surgical aperture. This can be accomplished by (a)
generating force along a line of action to retract the tissues to
achieve a desired surgical opening (the "retraction axis"), (b)
accommodating motions (e.g. translations and rotations) of the
retraction axis such that there is minimal opposing force from the
retractor to these motions, and (c) accommodating motions (e.g.
translations and rotations) of the retractor blades, and of the
underlying tissues, that are not parallel to the retraction axis
such that these non-parallel motions occur with minimal opposing
force from the retractor. To this end, the retractor should also be
as lightweight as is practicable. Thus, the retraction axis is free
to move in space and there is minimal force opposing motions not on
the retraction axis.
[0395] This can be accomplished by a lightweight retractor that is
free to move, or its parts are free to move, as the patient's body
exerts forces that are not along the retraction axis. Such a
retractor, thus, automatically aligns itself (e.g., its blades)
such that the retraction axis is always oriented along a direction
that achieves the desired surgical opening while reducing the
magnitudes of all forces.
[0396] Disclosed herein are apparatus and methods for automatically
minimizing the imposed deformation forces applied to the patient to
the minimum required for surgical access. With the various
embodiments of the present invention one can readily apply forces
sufficient to deform the patient's tissues in the manner
appropriate for medical procedures while minimizing forces arising
from or leading to undesired deformations of the patient's
tissues.
G.2 Swing Blade Retractor-Dual-thrust Lead Screws
[0397] FIG. 73 shows one embodiment of a retractor G68 that
possesses a new degree of freedom of motion, allowing the retractor
blades G76 to automatically realign to reduce forces that are not
parallel to the retraction axis. Retractor G68 is functionally
divided into three units: a dual-thrust lead screw G80, a first
retraction unit G70, and a second retraction unit G72.
Collectively, retractor G68 is referred to as a "Swing Blade
Retractor". The dual-thrust lead screw G80 is a lead screw having
at least left-hand threads on one end and right-hand threads on the
other end (such as those offered by the Universal Thread Grinding
Company, Fairfield, Conn.).
[0398] Each retraction unit G70, G72 is comprised of a retraction
body G78, G79 having hollow `female` threads that engage the
outside surface of the dual-thrust lead screw G80, a retractor arm
G74, G75, and a retractor blade G76, G77. The retraction bodies
G78, G79 have either a left-hand thread or a right-hand thread with
which to follow the travel of the threads on the outside of the
dual-thrust lead screw G80. When the dual-thrust lead screw G80 is
rotated, the dual-thrust lead screw's threads (which are engaged
with the threads in the retraction bodies G78, G79) force the two
retraction units G70, G72 to move away from each other to displace
the (now formerly) apposed tissues. Rotation of the dual-thrust
lead screw G80 about its long axis can be accomplished by any of
several means, including a hand crank mounted to one end of the
dual-thrust lead screw G80, a motor mounted to one end, a hand
crank attached to a gear inside one retraction body unit G78, or a
motor attached to a gear inside one body unit (or both). The gears
might be helical gears, crown gears, friction drives, or other
means permitting a retractor body to simultaneously drive
dual-thrust lead screw G80 rotation and follow the motions of the
threads on the outside of the lead screw.
[0399] Note that a dual-thrust lead screw G80 could be made to have
an arbitrary number of regions of both left- and right-handed
threads, with arbitrary pitches (and so advance ratios), such that
a plurality of retraction units G70 could be made to move all at
once on a single lead screw G80, at different speeds and directions
relative to one another. For example, one might wish to engage more
than two ribs at once, say, four or six, and move them all in
concert to distribute deformations and loading, and to prevent
crushing of soft tissues between sequential sets of ribs.
[0400] While away from the body of the patient and not locked
together, each of the Swing Blade Retractor's G68 retraction units
G70 and G72 is able to swing freely about the long axis of the
dual-thrust lead screw G80. Note that rotation of both retraction
units G70, G72 about the long axis of the dual-thrust lead screw
G80 is constrained when the Swing Blade Retractor G68 is placed
against the patient's body or if the retractor blades G76 and G77
are engaged with the tissues. The result of this constraint is that
when the dual-thrust lead screw G80 rotates, while both retractor
blades G76 and G77 are against or inside the patient's body, both
retraction units G70 and G72 move apart, opening the incision to
create the surgical aperture. Furthermore, if a crank or motor is
placed inside one retraction body G78 or G79 of only one retraction
unit G70 or G72, respectively, then both retraction units G70 and
G72 still move apart under rotation of the dual-thrust lead screw
G80. The retraction units G70 and G72 will come back together when
the dual-thrust lead screw's G80 direction of rotation about its
own long axis is reversed. Thus, a motor or crank in one retraction
body G78 of one retraction unit G70 can be used to rotate the
dual-thrust lead screw G80 and, thereby, drive both retraction
units G70 and G72 apart.
[0401] FIG. 74 depicts how a Swing Blade Retractor G68 has an
additional degree of freedom, relative to a conventional retractor,
such as those shown in FIGS. 67, 68A, 68B, and 70A through 70C. For
the Swing Blade Retractor G68, retraction units G78, G79 are
mounted to the dual-thrust lead screw G80 only by the threads in
each retraction body G78, G79, so the retraction units G78, G79 are
free to rotate about the long axis of the dual-thrust lead screw
G80. The retractor blades G76, G77 are, thus, able to rise and fall
in a direction G98 approximately perpendicular to the axis of
retraction G100 and perpendicular to the surface of the body of the
patient (i.e., in and out of the incision). In contrast, the arms
of a conventional retractor are always constrained to move towards
or away with respect to one another within that single axis of
retraction; any tendency of the retractor blades to move in any
other direction is strongly resisted by the substantial structure
of the retractor. Importantly, any tendency of the body wall in
contact with the retractor blades to move in some direction other
than the axis of retraction is also resisted by a conventional
retractor, and, subsequently, substantial stresses can form in the
body's tissues that are unrelated to the force required to obtain
the surgical opening. In other words, the minimum amount of force
and/or trauma to open the body wall might require a curved path, or
a slightly shifting path, as opposed to a unidirectional,
rectilinear path.
[0402] An additional advantage of a Swing Blade Retractor is that
it can assist insertion of the retractor blades into the incision
during preparation for retraction. When inserting the retractor
blades of the prior art into an incision through a patient's body
wall, the surgeon is forced, by the rigidity of the retractor
frame, to jam both retractor blades in at once. This is a problem
because this cannot be done until the surgeon first uses her
fingers to pry open the incision to be wide enough to be able to
fit in both blades, which may themselves have wide edges. However,
for the Swing Blade Retractor G68, because the two retraction units
G70, G72 swing freely and independently, each retractor blade can
be inserted one at a time as desired, allowing a surgeon to begin
with a smaller opening.
[0403] Another advantage of the Swing Blade Retractor G68 is that
the hollow threads of the retraction bodies G78, G79 can be formed
of more than one piece. For example, the hollow threads can be made
of two halves, each a semi-circle in section, that are brought
together inside the retraction body G78, G79 to enclose, embrace
and engage the threads of the dual-thrust lead screw G80. This
enables another improvement over the rack-and-pinion retractors,
which must be laboriously cranked back all the way shut to be
removed, in that one or both of the Swing Blade Retractor's G68
retractor bodies G78, G79 can be instantly removed from the
dual-thrust lead screw G80 by disengaging the two-piece hollow
threads. For example the two-piece hollow threads can separate such
that the dual-thrust lead screw G80 can pass through a gap made by
the separation. The means of thread disengagement might be a
button, lever, motor or flap that when closed retains and
stabilizes the threaded halves around the dual-thrust lead screw
G80. This enables the surgeon to rapidly lift one or both
retraction bodies G78, G79 away to clear the surgical field in an
emergency, facilitating removing the entire retractor G68.
Similarly, the hollow threads, rather than being composed of two
halves that fully or almost fully wrap the dual-thrust lead screw
G80, can engage only one side of the dual-thrust lead screw G80,
wrapping only 1!5th, for example, of the circumference of the
dual-thrust lead screw G80. This facilitates disengagement of the
threads from the dual-thrust lead screw G80--the threads need only
be lifted away from the dual-thrust lead screw G80 to permit free
motion of the retraction unit G70, G72 along the length of the
dual-thrust lead screw G80.
[0404] The advancement of the retraction bodies G78, G79 usually
proceeds from the rotation of the dual-thrust lead screw G80 about
the dual-thrust lead screw's G80 long axis. The rotation of the
dual-thrust lead screw G80 can be the result of a source of torque
such as a hand crank, a motor, or the like. The source of torque
can be external to the retraction body G78, G79. In one embodiment,
the source of torque is located inside one retraction body G78 or
G79. In this case, the retraction body G78 or G79 thus possesses
its normal capability to be driven along the dual-thrust lead screw
G80 while simultaneously being the agent that drives the rotation
of the dual-thrust lead screw G80 about its own long axis. For
example, one may modify the dual-thrust lead screw G80 by further
providing rotation means co-located with the threads along the
shaft so that the retraction body G78 or G79 may engage both the
threads for advancement and the rotation means for rotation. One
example of rotation means would be splines cut along the length of
the shaft. The threads of the dual-thrust lead screw G80 and
splines (not shown) can co-exist on the same driveshaft, are not
mutually exclusive, and can be engaged by separate mechanisms
housed within the retraction body G78 or G79. The hollow threads
disclosed above can provide the engagement for advancement upon
rotation of the dual-thrust lead screw G80, while a toothed ring
drive (not shown) surrounding the lead screw but engaging only the
splines provides the rotation. The hollow threads "see" only the
threads of the dual-thrust lead screw G80 while the toothed ring
"sees" only the splines, i.e., the surface gaps forming the splines
do not present occlusions to the threaded follower and the surface
gaps forming the threads do not present occlusions to the toothed
ring drive. This form of the dual-thrust lead screw G80, called a
splined dual-thrust lead screw, can be made by first cutting,
machining, or rolling helical threads into a plain metal rod or
cylinder, and then cutting splines in the same cylinder. Other
means are possible, but the intent is to provide in one device (and
even in one component of the device) simultaneous dual-thrust lead
screw G80 thread following and lead screw rotation.
[0405] Another benefit of the Swing Blade Retractor G68 design is
that it is self-aligning. For stability's sake, the Swing Blade
Retractor G68 exploits the tendency of the edges of the patient's
body wall to re-appose once separated. When a surgeon retracts the
body wall, the apposed or touching edges of the incision now move
apart. The body's mechanical reaction is tore-appose the edges of
the incision, i.e., the distance between the edges of the incision
"tries" to return to zero. Crucially, this re-apposition occurs in
three dimensions. No matter the initial orientation of the
retractor blades G76, G77, they cannot swing apart once engaged
with the patient's body wall; thus, the natural forces at work in
the patient's body automatically align the retractor blades G76,
G77 (and indeed, the entire axis of retraction G100) to exactly
that angle in three dimensions that minimizes the distance between
the retractor blades G76, G77, and so, the force required for
retraction.
G.3 Swing Blade Retractor-Roller Drives
[0406] FIG. 75 shows another means G104 for driving retraction
units in a retractor. Rather than using a dual-thrust lead screw, a
roller drive G106 is used. A roller drive combines thrust and
rotation, like a dual-thrust lead screw, but can be more efficient,
and it offers the ability to variably adjust the pitch of drive.
Roller drive G106 has three or more rollers G0110 engaging a shaft
G0114 with at least one of the rollers, a driver roller G112,
coupled to a torque source, such as a motor or a hand crank, and
with the other rollers G110 acting as idler rollers which passively
roll along the shaft G114. The rollers G110 and G112 can have
collars that help guide the rollers G110 and G112 along the shaft
G114, ensuring that the rollers G110 and G112 remain engaged with
the shaft G114. The shaft G114 can be substantially rectangular in
cross section, as in FIG. 75, or shaft G114 can have any other
cross-sectional shape matched to the rollers G110 and G112. The
rollers G110 and G112 are forced against the shaft G114 such that
friction between the driver roller G112 and the shaft G114 causes
the driver roller G112 to impel the shaft G114 when the driver
roller G112 rotates under the action of its torque source. Note
that motion is relative, so the roller drive G112 can move along a
stationary shaft G114, or a shaft G114 can be pushed by a
stationary roller drive G112. The rollers G110 and G0112 can be
fitted with appropriate bearings to permit substantial force
pushing the rollers G110 and G112 against the shaft G114 to
generate substantial friction between the shaft G114 and the driver
roller G112. The rollers G110 and G112 can be forced against the
shaft G114 either by precise manufacture of the mounts holding the
rollers G0110 and G112, or the rollers G110 and G112 can be pressed
into position by, for example, a cam that variably moves the
rollers G110 and G112 away from the shaft G114, releasing the
shaft, or presses rollers G0110 and G112 against the shaft G114 to
hold or drive the shaft G0114.
[0407] FIG. 76 shows how a roller drive G106 can be used in a
retractor G116. Retraction unit G17 has a roller drive comprised of
a first idler roller G120, a second idler roller G121, and a drive
roller G124. Idler rollers G120, G121 and drive roller G124 engage
shaft G122, and torque on drive roller G124 drives retraction
against the retraction force G126 from the tissues. This
configuration of idler rollers G120, G121 and drive roller G124
provides several advantages. First, retraction force G126 results
in a torque G118 on retraction unit G117 that then applies a force
G128 on the drive roller G124 and the first idler roller G120 that
increases drive friction for drive roller G124, thereby improving
engagement between the driver roller G124 and the shaft G122.
[0408] Second, the shaft G124 is smooth, decreasing chances for
snagging items in the surgical field. Fourth, the rollers G120,
0121, and G124 and shaft G0122 are easier to manufacture precisely,
decreasing cost.
[0409] FIG. 77 shows another embodiment of a roller drive G130. The
idler rollers G138 and drive roller G139 do not have collars as in
FIGS. 75 and 76; rather, the idler rollers G138 and are circular
cylinders. In FIG. 77, the shaft G136 is circular in cross-section.
The rollers G138 have an axis of rotation G140 defining the
orientation of rotation G142 of the rollers G138. On the left-hand
side of FIG. 77, the rollers G138 and shaft G136 are configured
such that the roller axes of rotation G140 are all perpendicular to
the long axis of the shaft G136; thus, when the driver roller is
actuated, the shaft moves out of the page plane (see
rotation-indicating arrows). On the right-hand side of FIG. 77, the
roller axes of rotation G140 are aligned oblique to the long axis
of the shaft G136; thus, when the driver roller G139 is actuated,
the shaft G136 moves helically out of the page plane. In other
words, the motion of the shaft G136 imparted by the rollers G138
and G139 has two components, one that translates the shaft G136 out
of the page plane and one that rotates the shaft G136 around the
long axis of the shaft G136.
[0410] FIG. 78 shows that the relative degree of each motion of the
shaft (translation and rotation) is determined by the angle between
the roller axis of rotation G140 and the long axis of the shaft
G136. The angle between the roller axis of rotation G140 and the
long axis of the shaft G136 is shown to vary from left to right in
FIG. 78. On the left-hand of FIG. 78, the roller axis of rotation
G140 is perpendicular to the long axis of the shaft G0136 resulting
in translation of the shaft directly out of the page towards the
viewer (without rotation). On the right-hand of FIG. 78 roller axes
of rotation G140 are perpendicular to the long axis of the shaft
G136, resulting in rotation of the shaft G136 within the plane of
the page (without translation) when the rollers' axes of rotation
G140 are parallel to the long axis of the shaft G136, and the shaft
G136 cannot be moved through the rollers G139, G140 regardless of
whether rollers G139, G140 are turning, i.e., the shaft G136 is
locked, thus this embodiment of the retractor G130 is
self-retaining. At all other angles between the roller axis of
rotation G140 and the long axis of the shaft G136, rotation of the
rollers G139, 0140 results in a combination of rotation and
translation of shaft G136.
[0411] Note in FIG. 78 that varying the angle between the rollers'
axes of rotation G140 and the long axis of the shaft G136
effectively varies how the driver roller's G139 power is
spent--when the roller axis of rotation G140 is perpendicular to
the long axis of the shaft G136, all of the power of driver roller
G139 is spent translating the shaft G136, and when the roller axis
of rotation G140 is parallel to the long axis of the shaft G36, all
of the power of driver roller G139 is spent rotating the shaft G136
in place. In motions in which one motion (translation or rotation)
of the shaft G136 is strongly opposed and the other motion is not,
then varying the angle between the roller axes of rotation G0140
and the long axis of the shaft G136 effectively gears the roller
driver G130, allowing the roller driver's axis of rotation G140 to
be adjusted such that the power of the roller driver G139 is
sufficient to generate the desired force and motion. For example,
the roller axes of rotation G140 can initially be parallel to the
long axis of the shaft G136 when the torque source of the driver
roller G139 starts rotating the driver roller G139. This causes the
shaft G136 to rotate without translation. While the driver roller
G139 continues rolling, the angle of the roller axes of rotation
G140 can be continuously changed such that the shaft G136 slowly
starts translating. The angle of the roller axes of rotation G140
can, thus, be adjusted to place more of the power of the driver
roller G139 into translating the shaft G136. Note that controlling
the angle between the rollers' axes of rotation G140 and the long
axis of the shaft G136 can also be used to control the velocity of
translation of the shaft G136.
[0412] FIG. 79 shows one embodiment that uses roller drives in a
retractor G160. Retractor G160 has two opposed retraction units a
first retraction unit G161 and a second retraction unit G162, each
comprised of a retractor arm G168 and G170, respectively, and a
retractor body G183 and G182, respectively, mounted on shaft G184.
Consider first retraction unit G161: retractor body G183 houses a
roller drive G171 comprised of two idler rollers G172 and a drive
roller G175, each oriented with its roller axis G176 of rotation
oblique to the long axis of the shaft G184. The second retraction
body G182 contains a set of three idler rollers G172, each oriented
with its roller axis of rotation G176 oblique to the long axis of
the shaft G184. Both retraction units G161 and G162 are, thus,
driven by the one drive roller G175 in the first retraction body
G183. The angle between the rollers' axes of rotation G176 in the
first retraction body G183 and the long axis of the shaft G184
determines the motion G186 of the shaft G184 relative to the
retractor body G183. The motion G186 of the shaft G184 can be
broken into its two components of rotation G189 and translation
G187 relative to first retractor body G183 and rotation G190 and
translation G188 relative to second retractor body G182. The second
retraction body G182 does not drive the shaft G184; rather, the
rotation of the shaft G184 drives the translation G188 of the
second retraction body G182 and, thus, the second retraction unit
G162. Engagement of the retractor arms G168 and G170 with the
patient's tissues prevents rotation of the second retraction unit
G162 about the long axis of the shaft G184, so the angle between
the rollers' axes of rotation G176 in the second retraction body
G182 determines the translation rate G188. Thus, the driver roller
G175 in the first retraction body G183 drives apart both retraction
units G161 and G162 with a relative velocity of G187 plus G188,
thereby providing retraction G164, G165.
[0413] Note that the angle between the rollers' axes of rotation
G176 and the shaft G184 in the first retraction body G183 need not
match the angle in the second retraction body G182. The angle can
be such that the first retraction body G183 generates only rotation
of the shaft G184, and the angle in the second retraction body G182
can be such that the second retraction unit G162 moves away from
the first retraction unit, or any other range of combinations.
Infinitely fine and smooth control of the rate of retraction by the
rate of rotation of the driver roller (e.g. by a motor that
actuates it) is thereby achieved by varying the angle between the
rollers' axes of rotation G176 and the shaft G184 in the first
retraction body G183, and also by varying the angle between the
rollers' axes of rotation G176 and the shaft G184 in the second
retraction body G182. A mechanism that variably changes the angle
between the rollers' axes of rotation G176 and the shaft G184 in
either or both retraction body G182, G183 can thus be used to
control both the rate of retraction and the magnitude of the thrust
(retraction force).
G.4 Dovetails
[0414] Another embodiment of a retractor G190 is shown in FIG. 80.
Retractor G190 uses an alternative means for providing additional
degrees of freedom of motion to the retractor arms G194. The two
arms G194 of retractor G190 are mounted to the frame G192 of the
retractor G190 via dovetail slides G196 and G198, the axes of which
are perpendicular to the axis of the motion of the retractor blades
(i.e., the axis of retraction). Each retractor arm G194 is thus
free to slide out and back, i.e., perpendicular to the axis (or
direction) of retraction. Much of the forgoing concerning the
features and benefits of the Swing Blade Retractors G68 and G160
and applies here, except that the accommodating motions G200 of the
retractor blades G199 enabled by the dovetails G196, G198 can be
perpendicular to that of the Swing Blade Retractors G68 and G160.
Additionally, the motions G200 are directly translational as
opposed to rotational, as was the case for the Swing Blade
Retractors G68 and G160, and the two may be combined as desired to
increase a retractor's ability to accommodate the patient's
reconfiguring tissues.
[0415] FIG. 81 shows another retractor G202 that is fitted with two
dovetail slides. First dovetail G204 permits motion G208 of
retractor arm G214 and retractor blade G216, matching the motion
G200 of dovetails G0196, G198 in FIG. 80. Second dovetail G206
permits motion G210 of retractor arm G214 in a direction at right
angles to the first dovetail G204, with both motions G208 and G210
being perpendicular to the axis of retraction. This means that this
retractor can accommodate both a rise and fall of the body wall and
a relative sliding of the edges of the incision parallel to the
incision and within the plane of the skin of the patient, while
still delivering retraction forces to the patient's body wall. This
design still achieves stability and force minimization (now in 2
axes) by exploiting the tendency of the patient's body wall to
re-appose.
[0416] G.S Parallelograms
[0417] In yet another embodiment of a retractor G218 shown in FIGS.
82A and 82B, another mechanism is disclosed for providing an
additional degree of freedom to the retractor arms G224, G226.
Retractor G218 is comprised of two parallel dual-thrust lead screws
G230 and G232 held by captured swiveling nuts G228 in a first
retraction body G220 and a second retraction body G222. Each
retraction body G220, G222 bears a retractor arm G224, G226, and a
retractor blade G250, G252. Captured, swiveling nuts G228 are
similar to those found in a Jorgenson clamp used for woodwork, such
as those offered by Woodworker's Supply of Albuquerque, N. Mex.
These captured, swiveling nuts G228 allow movement G254 of the
retractor blades G250, G252 in a direction approximately
perpendicular to the axis of retraction G256 (see FIG. 82b).
G.6 Tension Straps
[0418] Another embodiment is shown in FIG. 83, which shows a
different retractor configuration we call a "tension strap
retractor" G258 that automatically aligns to the forces on the
retractor blades G264. Tension straps include mechanisms integral
to the strap that are capable of generating the force for
retraction. Here, the retractor G258 takes the form of two or more
thin straps, cranial strap G262 and caudal strap G266, that wrap
around, and maybe behind, a portion of the body of the patient
G260. Cranial strap G262 and caudal strap G266 are connected to
retractor blades G264 which are inserted into the incision G269 to
pull on the cranial rib G263 and caudal rib G265. The cranial strap
G262 can be held in position by wrapping around a portion of the
patient's G260 body, such as around the neck and/or shoulder. The
caudal strap G266 can be held in position by wrapping around a
portion of the patient's G260 body, such as around one leg.
Alternatively, the straps G262 and G266 might anchor on the dermis
of the patient G260 or on a bedframe. In this embodiment, retractor
G258 self-aligns with the natural resistance of the body wall.
Tension strap retractor G258 operates in tension, as opposed to a
traditional compression- and bending-resisting frame. One benefit
of a tension strap retractor G258 is that the volume of material
required to withstand the retraction forces in tension is a small
fraction of the volume of material required to withstand similar
forces in, say, bending. Given this, a tension strap retractor can
be very lightweight, further reducing unnecessary loading of the
patient's tissues.
[0419] FIGS. 84 and 85 show another embodiment of a tension strap
retractor G270 adapted for sternotomy. FIG. 84 shows a front view
of tension strap retractor G270, and FIG. 85 shows a
cross-sectional view through a patient's body G272. Tension strap
retractor G270 simply wraps around behind the back of the patient
G272 and automatically orients to open up an incision G275 that
bisects the sternum into two halves G281 and G282. Retractor blades
G278 and G280 reach into and/or around the margin of the incision
G275, pulling back on sternum halves G281, G282. Tension strap
retractor G270 pulls along the surface of the body of the patient
G272. In this arrangement, the straps G274, G276 and G306 of the
tension strap retractor G290 load the body wall such that straps
G274, G276 and G306 remain aligned with the body wall and, thus,
with the retraction forces for opening incision G275.
[0420] For tension strap retractor G270, the straps can be any thin
and strong fabric, such as nylon webbing, that can resist tension.
The straps can develop tension via a pull strap with sliding
buckle, a ratchet pull, a winch, or by direct shortening of the
fibers of the strap (for example by using shape memory alloy for
the fibers). To this end, the strap might be fibrous netting
surrounding pressure bladders G296, for example elastomer balloons
residing within two-layer (or hollow) nylon webbing. In this case,
the netting can be formed of fibers that run helically around the
strap G276, G278, and G306 as a whole. In this example, the
trajectory of the helical fibers forms an angle with respect to the
path of the main strap; the angle can be very low (10 to 30
degrees) to facilitate developing significant force when the
bladders G296 are inflated. Retraction forces can be generated by
inflation alone if desired. Inflating the pressure bladders G296
would swell them, developing tension in the straps G276, G278, and
G306, and so loading the retractor blades G278 and G280. The
swollen bladders G296 can also provide a moment enhancer G303
(i.e., a stand-off) to reduce the magnitude of the tension that
must be developed to create the forces sufficient to operate the
tension strap retractor G290. Alternately, the stand-off G303
function might be achieved more directly by placing pads, pillows,
blocks, or other compression-resisting members between the straps
G276, Gs78, and G306 and the body of the patient G272. Saddles and
pads can be added to the straps G274, G276 and G306 to distribute
loading of the straps over the patient's body G272, or to
concentrate the loads in particular areas, for example those areas
that can withstand more concentrated pressure.
[0421] Another advantage of the tension strap retractor G270 is
that it offers greater access to the surgical field because it has
few components near the surgical field and these components lay
close to the body of the patient G272 with tension strap retractor
G270 having an extremely low profile, perhaps projecting no taller
than 2 or 3 millimeters above the skin of the patient.
[0422] Tension strap retractors G290 can also be used for
non-thoracic surgery. A common use of retractors, such as a
Weitland retractor G312 (see FIG. 86) is to pull open an incision
through the skin G314 to provide access to the anatomy beneath the
skin for plastic surgery, orthopedic surgery, neurosurgery, and
others. Retraction of the skin frequently requires only small
forces, but conventional retractors in the prior art, such as a
Weitland retractor G312, are typically scissor-like devices made of
steel and are heavy, thereby interfering with surgical access and
exerting umlecessary loads, especially during the second phase of
retraction.
[0423] FIG. 87 shows a tension strap retractor G320 that is small
and lightweight to, for example, open the skin on an arm for
vascular surgery. The tension for retraction of the retractor
blades G326 and G332 can be generated by pull tabs G324 and G334
that pull the strap G322 through a self-cinching buckle G328 and
G330. Alternatively, tension could be generated by pulling the
strap through a loop and then securing back onto the strap with
Velcro.
H. Hard Tissue Engagers
[0424] Retractors, by their very nature, are typically made of
rigid stainless steel to withstand the stresses of forcing open
incision, including incisions through rigid structures like rib
cages. Rib cages are themselves made largely of rigid bone and
built to withstand the stresses of human locomotion or lifting
large loads. The ribs, as it happens, are intermingled with several
much softer tissues, including muscles which provide actuation for
breathing and modifying posture, connective tissues which transmit
forces from one rib to another and to the spinal column, vessels
and arteries which supply nutrients and remove waste products,
nerves providing signaling to and from the spinal chord; and all
these are covered with skin and adipose tissues. During a
thoracotomy in which a surgeon inserts the retractor blades and
then cranks to spread the patient's ribs apart, the muscles apposed
to those ribs and the nerves running along the surface of those
ribs are often damaged when compressed between the rigid rib and
the metal blades of the retractor. The soft tissues, supposedly
protected by the ribs, are instead caught in the middle when the
retractor blades push against the bones during retraction.
[0425] In more detail, our ribs lie in a closely packed row deep
under the skin, spaced about as far apart as they are wide, forming
serial bony bars embedded in the muscle and other soft tissues that
the ribs in turn support. As shown in FIG. 88A, running under the
skin H42, cranial rib H46 and caudal rib H47 are roughly oval in
cross section with the long axis of the oval aligned more-or-less
parallel to the surface of the skin H42. (The following description
uses the terms "caudal" H45 and "cranial" H43, which refer to
relative position in the body, with cranial being closer to the
head and caudal being closer to the feet.) Intercostal tissues H44,
which are mostly muscle and connective tissues, span the space
between the cranial margin H54 of the caudal rib H47 and the caudal
margin H50 of the cranial rib H46. A delicate bundle of nerves and
arteries (the neurovascular bundle H48, which includes the
intercostal nerve, lays just inside the caudal margin of each rib
H46, H47.
[0426] Surgeons, aware that the neurovascular bundle H48 can be
easily damaged, prepare to insert the retractor by slicing the
intervening intercostal tissues H44 closer to the cranial margin
H54 of the caudal rib H47. This lessens the probability of
accidentally cutting the neurovascular bundle H48 during the
incision, and it provides a pad of muscle on the caudal margin H50
of the rib H46 that is cranial to the incision H52, in order to
protect the neurovascular bundle H48.
[0427] As shown in FIG. 88B, the retractor is inserted into the
incision H52, with retractor blades H30 positioned to push against
the two ribs H46 and H48. Retractor blades H30 are attached to
retractor arms H32 by fasteners H38 such that retraction pries
apart the ribs H46, H47 when retraction arms H32 separate during
the first phase of retraction.
[0428] Damage to the neurovascular bundle H48, nevertheless,
occurs. As depicted in FIGS. 89 and 90. FIG. 89 shows a
cross-sectional view, and FIG. 90 shows a top view. Regions of high
pressure H60 are created in the intercostal tissues H44 that are
compressed between the ribs H46, H47 and the hard retractor blades
H30. The pressures are large, owing to the large forces used to
separate the ribs. Subsequently, tissues are mechanically crushed.
The neurovascular bundle H48 can be pinched, especially at pinch
points H82 created by the edges (i.e., corners) of the blades H30
where they intersect the ribs H46 and H47. The tissue pressures
underlying the retractor blades H30 can be sufficiently high to
block both blood flow through the vessels of neurovascular bundle
H48 and perfusion of all this tissue underlying the retractor
blades H30. Lack of perfusion causes anoxia in theses tissues,
which damages all tissues, especially nerves.
[0429] Additionally, movement of ribs H46, H47 during retraction
can be sufficiently large that a rib H46, H47 can impinge on the
adjacent rib further from the incision, as shown in FIG. 91. Again,
the resulting regions of high tissue pressure H60 between ribs can
be sufficiently large that intercostal tissues H44, including the
intercostal nerves in neurovascular bundles H48, can be damaged one
or even several ribs removed from the incision (Rogers, Henderson
et al. 2002).
[0430] The regions of high pressure H60 and the pinch points H82
are established during the first phase of retraction and are then
sustained during the second phase of retraction for the duration of
the surgical procedure, which can often be hours.
[0431] Damage to intercostal tissues caused by the regions of high
pressure H60 and by pinch points H82 is thought to underlie much of
the pain caused by thoracotomies, especially damage to the
intercostal nerves of the neurovascular bundles H48. Thoracotomies
are considered one of the most painful of all surgical procedures.
Pain is always intense for days after surgery and, unfortunately,
can last for months to years, and sometimes is permanent. The
long-lasting pain after a thoracotomy has lead to the
identification of a "post-thoracotomy pain syndrome".
[0432] This great pain following thoracotomies, and the associated
morbidity and mortality, are the main drivers for alternatives to
these open-chest procedures, including minimally invasive surgery
(MIS). While many MIS procedures have been developed, such as
mini-thoracotomies, endoscopic surgeries, and the like, their
adoption rates have been low.
[0433] An improved retractor blade that decreases tissue damage
during retraction, especially to the intercostal nerve, would be of
great benefit. It would reduce post-operative pain while retaining
full surgical access.
[0434] To these ends, we disclose apparatus and methods for
attaining favorable alignments and positive engagements with a
patient's hard tissues, for example bones (e.g. ribs) or teeth.
With the various embodiments of the present invention one can
rapidly and assuredly apply forces sufficient to displace or deform
the patient's tissues for medical procedures while entirely
avoiding compressing, crushing, or compromising adjacent soft
tissues, thus preventing post-surgical pain.
[0435] In one embodiment shown in FIG. 92A and FIG. 92B, holes H118
are drilled from above into the ribs H46 and H47 and rigid posts
H120 are inserted into these holes to serve as anchors for the
retractor. Holes H118 can be drilled at an angle H119 such that,
after the posts H130 are inserted, the posts possess an angle with
respect to the axis of loading to ensure the posts don't slip out
of the holes during retraction. The posts H120 can be made such
that they snugly fit into the holes H118 to ensure good purchase in
the bone of ribs H46 and H47. Optionally, the posts H120 can
possess threads and be screwed into position in the ribs H46 and
H47 to ensure good purchase in the bone of ribs H46 and H47. A jig
can be used when drilling the holes to ensure appropriate angle,
depth, and position of the holes H118.
[0436] As shown in FIG. 92C, the posts H120, after placement in the
holes Hl18 drilled in the ribs H46 and H47, are then used as secure
anchors for retractor arms H11100 that push against the posts H120
to move the ribs H46 and H47 without pushing on soft tissue. The
posts H120 can be used for closing the incision as well.
[0437] Another embodiment is shown in FIG. 93. The posts H1160 are
attached by mechanical fasteners H166 to the retractor arms H170.
Also, the holes H155 are drilled all the way through the ribs H46,
H47. Note that different depths of the holes H155, including holes
that pass through the ribs H46, H47, can be used with any
configuration of posts H160. Note, also, that when the holes H155
are drilled all the way through the ribs H46, H47, holes HI 55 can
be used during closing, whereby sutures pass through the holes HI
55, running from caudal rib H47 to caudal rib H46 tore-appose the
ribs and to secure them into position. (It is prior art that such
holes are drilled specifically for re-apposing and securing the
ribs with sutures, but the holes are not used for retraction.)
[0438] FIGS. 94A and 94B show another embodiment of a device to
engage ribs but for which holes need not be drilled. Rather,
elastic circumferentially surrounding clips H192 can be attached to
the ribs H46, H47 such that each rib H46, H47 is firmly clasped
without exerting pressure on soft tissues H44 surrounding ribs H46,
H47. As shown in FIG. 94A, clip H192 possesses points, or spikes,
including a top spike H196 that engages the outer surface of the
rib H46 and a bottom spike H1194 that engages the inner surface of
the rib H46. The spikes H194 and H196 automatically seat onto or
into the surface of the bone (i.e., rib H46), crucially, away from
the neurovascular bundle H48. The clip H192 is attached to a
descenders H186 that are attached to retractor arm H182 by
mechanical fasteners H1184. Descender H186 descends from the
retractor arm H182.
[0439] Clip H192 is attached to descender H186 by a flexibly
bendable, tensily stiff element, such as cable or chain H188, which
runs tangentially around and attaches to the clip H192 at point
H190. Clip H1192 is hooked into, and so loads, the ribs H180. The
clip H192 possesses a roughly even radius that is a function of the
tension in the chain HI 88, that is, the radial distance separating
the clip H192 from the surface of the rib H46 changes as the
tension in the chain H188 changes. Use of descender HI 186 ensures
an advantageous angle for pulling on the chain H188 around the
circumference of the clip H192. When the spikes H194 and H1196 are
loaded for retraction of the rib H46, by tension on the chain H188,
the resulting torque on the clip H192 acts as if to rotate the
entire clip H192. But, since the clip's H192 rotation is largely
restrained by the spikes H194 and H196 inserted onto or into the
surface of the rib H46, the torque instead causes the clip H192 to
"rise up on tiptoes," i.e., the elastic circumferential clip H192
increases its radius away from the surface of rib H180, doing so by
angling the spikes H194 and H196 and firmly driving the spikes H194
and H196 into the bone H46, thereby more securely engaging with the
rib H46. Bottom spike H194 effectively serves as a pivot point for
the clip H192 which, when combined with rotation H191 of the clip
H192, forces the top spike H196 into the bone H46. Thus, slippage
of the clip H192 is prevented by the spikes H194 and H196, and
sufficient force can be exerted on the rib H46 to achieve
retraction without loading the soft tissues H44, including the
neurovascular bundle H48.
[0440] As shown in FIG. 94B, clips are placed on the both ribs H46
and H47 on both sides of the incision H52, and retraction moves the
ribs apart.
[0441] FIGS. 95A and 95B illustrate different configurations of
spikes on clips to achieve more secure engagement with the rib.
FIG. 95A shows a clip H192 like those in FIGS. 94A and 94B. Clip
H192 has single spikes H194, H196. Alternatively, FIG. 95B shows
that a clip H256 can have multiple spikes on each end, double
spikes H258 and H260 in this example, which distribute loading of
the spikes H188 on a rib and also prevent sideways rolling of the
clip H256 if chain H188 should pull a bit sideways.
[0442] Clips H192 and H256 are positioned after the intercostal
incision is made, and then the chains H188 are attached to the
descender H186. Similarly, the chains H188, or other tensile
element, can be attached to the descender H186 with sufficient
length of chain H188 to provide slack during placement of the clip
H192 or H256. After placement of the clip H192 or H256, the slack
is then removed before retraction commences. Removal of the slack
can be by any of several one-way slip attachments, such as a
ratcheting cable tie or "zip tie" as offered for sale by Nelco,
Inc. of Pembroke, Mass.
[0443] FIG. 95 illustrates the placement of one or more clips to
distribute loading along the ribs during retraction. Multiple
single spike clips H192 are placed on each rib H46 and H47,
possibly with different numbers on each rib H46 and H47. Multiple
clips H192 are attached to retractor arms H182 and are, thus,
spaced along the rib margin facing the incision H52. When retractor
arms H182 move apart during retraction, the multiple clips
distribute loading of the rib to decrease the chance of rib
fracture.
[0444] FIGS. 97A through 97D show another embodiment of a device
that engages the ribs directly, minimizing trauma to intercostal
tissues. FIG. 97A shows a side view and FIG. 97B shows a top view.
A device can cut through soft tissues H44 to abut hard tissues. The
cut through the soft tissues is a small trauma relative to the
compressive loading of a larger retractor blade. Retractor arms
H300 can have descender posts attached, a first descender post H304
abutting cranial rib H46 and a second descender post H306 abutting
caudal rib H47. Descender posts H304 and H306 can have their
positions adjusted (arrows H314 and H316) closer or farther from
the centerline of the incision H52 (i.e., left-right in FIGS. 97A
and 97B) to permit automatic balancing of loads as disclosed in
Section F. Descender posts H304 and H306 can have sharpened edges
H310 and H312, respectively, that face the ribs H46 and H47,
respectively, such that the descender posts H304 and H306 can
penetrate laterally through the margin of soft intercostal tissues
H44 to abut the ribs H46 and H47 directly. Thus, rather than crush
the intercostal tissue, descender posts H304 and H306 slice into
the intercostal tissues H44. Because descender post H302 has a
vertically straight margin oriented towards the cranial rib H46,
descender post H302 can abut the cranial rib H46, but does not
impinge on the neurovascular bundle H48 that lies just underneath
the caudal edge of the cranial rib H46 (see FIG. 97A). The sharp
edges H310, H312 of descender posts H304, H306 can be serrated, or
possess other structures to engage the ribs, to prevent the
descender post H304, H306 from slipping off the rib H46, H47.
Alternatively, FIG. 97C shows a different descender post H334
descending from retractor arm H330. Descender arm H334 has a
retraction hook H336 to facilitate positioning against the rib H46
and to prevent slipping. Preferably, such structures include
appropriate stand-offs H338 and curvature such as to create a
hollow H340 to avoid impinging on the neurovascular bundle H48.
[0445] Descender posts can be mounted to the retractor arms such
that their positions can be adjusted left-right (indicated by
arrows H314 and H316 in FIGS. 97A and 97B), variably pushing
through the soft tissues H44 at the margins H320 of the incision
H52 to accommodate curvature of the ribs H46, H47 and thereby
ensure distribution of loads on the ribs H46, H47. Any of the
embodiments disclosed in Section Fare appropriate. Additionally, as
shown in FIG. 97D, a retractor arm H330 can have descender posts
H350 and H352 attached by lockable, telescoping, rotatable mounts
H354. Thus, after the descender posts H350 and H352 have been
placed into an incision, each descender post H350 or H352 can be
swung up against the rib H46, telescoped by a motion shown by arrow
H356 to bring the hook H336 into contact with the bottom of the rib
H46, and then locked into position.
[0446] Refer now to FIGS. 98A and 98B which show another embodiment
using retraction hooks that have an additional degree of freedom of
motion facilitating placement onto the rib. FIG. 98A shows a side
view, and FIG. 98B presents a top view showing the steps of placing
the retraction hook onto the rib. Consider FIG. 98A, a descender
post has a shaft H366 that attaches to retractor arm H364 via
swivel joint H374. Shaft H366 has a Retraction hook H336, including
a stand-offH338, that extends under the rib H46 and forms a hollow
H340 to avoid contact with or compression of neurovascular bundle
H48. Swivel joint H374 permits rotation H376 of shaft H366 around
an axis of rotation H375 parallel to the axis of the shaft of the
descender post H366 (as shown in FIG. 983A). As shown in FIG. 98B,
Step 1 (block 390), the retraction hook H336 on shaft H366 can be
aligned such that, before insertion into the incision H52, the
retraction hook H336 is parallel to both the rib H46 and the
incision H52. In Step 2 (block 392) of FIG. 98B, after insertion
into the incision H52, the retraction hook H336 can be rotated to
position the retraction hook H336 under the rib H46. Additionally,
the length of the shaft H366, or the distance between the
retraction hook H336 and the retractor arm H364, can be adjusted
(arrow H378), as shown in FIG. 98A, to further permit positioning
of the retraction hook H336 relative to the rib H46.
[0447] FIG. 99 shows a three-dimensional working model of a
retractor H412 equipped with first and second retractor arms H414
and H416, respectively, each having three (3) descender post shafts
H366 with rotatable, height-adjustable, retraction hooks H336.
[0448] FIG. 100 discloses yet another embodiment having a plurality
of descender posts to distribute loads on a rib. Descender posts
H428 can be very thin, each not capable of displacing the rib H46,
but with several arrayed in parallel on retractor arm H426 such
that, combined, descender posts H428 can displace the rib H46.
Descender posts H428 can be, for example, stiff wires arrayed into
a comb that can be placed against the rib H46. The descender posts
H428 can be sufficiently sharp on their ends that they are placed
by piercing the soft tissues H44 next to the rib H46. The positions
of the descender posts H428 can be independently adjustable, or
they can be flexible such that they automatically seat against the
rib. As also shown in FIG. 100, the shape of the descender posts
H428 can be such that they press against the rib H46 without
impinging on the space below it, thus again avoiding loading the
neurovascular bundle residing in the soft tissues H44 there. Any
number of hard tissue engagers can be arrayed to avoid crushing,
damaging, or traumatizing any soft tissues associated with a hard
tissue.
[0449] FIGS. 101A through 101E show another embodiment of a device
for engaging a hard tissue, like a rib, without damaging
neighboring soft tissues. Retractor arm 432 has a descender post
H434 with a turn or bend H435 going to a projection H436 that
engages the rib H46. The projection H436 is thin and pointed such
that it easily penetrates the soft tissues H44 adjacent to the rib
H46. The projection H436 can include a tip H442 with a sharp point
to engage the edge of the rib H46 such that projection H436 of the
descender post H434 firmly engages rib H46 but does not touch the
neurovascular bundle H48. As shown in FIGS. 1018 through 101D, the
sharp point of tip H442 can be configured such that it pierces only
the surface of the rib H46 to prevent slipping, but can not pierce
further. For example, as depicted in FIG. 101C, the tip H442 of the
projection H436 can terminate with a spike H470 that penetrates the
rib H46, but the tip of the projection itself H442 it too dull to
further penetrate the rib H46. As shown in FIG. 101D, the tip H442
can have multiple spikes H472 to ensure engagement of the rib H46.
As shown in FIG. 101E, projection H436 is depicted engaging the rib
H46 with a spike H470, which ensures engagement of projection H436
with rib H46 even as rib H46 moves (shown by arrow H488).
[0450] FIG. 102 shows a section view of a thoracotomy performed by
another embodiment in which the rib is firmly grasped on both sides
to permit deterministic control of its motion, i.e. the position
and orientation of the rib is always controlled. Retractor arms
H500 each have a spacer bar H506 to which are attached paired
descender posts H502 and H504. The paired descender posts H502 and
H504 engage both sides of the ribs (for example, H46). The
directions of retraction (i.e., rib spreading) are shown by arrows.
Both descender posts H502 and H504 are straight and engage the ribs
H46 laterally. The sides of the descender posts H502 and H504 can
have serrations H503 where they engage the ribs to reduce slipping
of the descender posts H502 and H504 on the ribs H46. The distance
H491 separating the paired descender posts H504 and H502 can be
adjustable to permit positioning the paired descender posts H502
and H504 firmly against the margins of rib H46 thereby
accommodating variations in cranial-caudal width of rib H46. This
embodiment allows a retractor to firmly grasp the rib H46,
permitting deterministic control of rib position throughout
retraction.
[0451] Referring now to FIG. 103, a retractor H510 can also engage
ribs H519 and H525 further from the incision H526, in addition to
the ribs H521 and H523 adjacent to the incision. As shown in FIG.
103, a retractor H510 can possess a plurality of retractor arms
(H528, H530, H532 and H534), each equipped with descender posts
(H529, H531, H1533 and H535, respectively). The retractor arms
H528, H530, H532 and H534 can have coordinated motion, with respect
to one another, that includes different speeds such that the
retractor arms H528, H530, H532 and H534 each effect a different
displacement over the same time. For example, retractor arms 1
(H528) and 2 (H530) form a pair on one side (the cranial side,
H537) of the incision H526, and both retractor arms 1 (H528) and
retractor arms 2 (H530) can move in the same direction of
retraction (H536), but the displacement (H511) of retractor arm 1
H528 can be less than the displacement (H513) for retractor arm 2
H530 (e.g., retractor arm 1 can move more slowly than retractor arm
2). (Retractor arms 3 H532 and 4 H534 can, similarly, form a pair
on the opposite, or caudal H539, side of the incision H526.) This
varying displacement of the retractor arms reduces the pressure in
intercostal space A H520 and intercostal space B H522 (and their
respective neurovascular bundles, grouped H524) arising from ribs
H518, H519 and H521 (cranially) and H523, H25 and H527 (caudally)
impinging on one another during retraction.
[0452] FIGS. 104A, 104B and 104C show another embodiment in which
an articulating clip is used to grasp a rib without compressing
neighboring soft tissues. FIGS. 104A through 104C show an action
sequence of an articulated clip H553 meeting, closing, and locking
down onto a rib H46. In the sequence, a descender post H544 is
fitted with a moveable, deeply curved, articulated clip H553 having
a top half jaw H554 and a bottom half jaw H555 attached by a pivot
H546 to the descender post H544. Each half H554 and H555 possesses
a sharp point H562 and H560, respectively, for engaging the rib
H46, and a tab (one tab, H556, projects up and is associated with
the bottom clip half H555, and another tab, H558, projects down and
is associated with the top clip half, H554. The clip halves H554
and H555 can be spring-loaded such that they stay open (with jaws
spread wide) before loading (i.e., before contacting the rib H46).
The clip half tabs H556 and H558 are earns shaped so as to generate
a torque when the descender post H544 with all associated
components is pushed against the rib H46. When the rib H46 impinges
on the clip half tabs H556 and H558, each tab is pushed apart and
away from the other, causing each half of the clip H554 and H555 to
rotate in the opposite direction (i.e., the top half clip H554
comes down and the bottom half clip H555 comes up), thus using the
force applied by the rib H46 to bring the sharp points H560 and
H562 into position against the rib H46 to forcefully secure it. The
shapes of tabs H556 and H558 cooperate with that of the clip jaw
halves H554 and H555 such that a space is created protecting the
neurovascular bundle H48 from any contact while retraction
proceeds. The sharp points H560 and H562 are configured such that
they penetrate only the surface of the rib H46, far behind the
neurovascular bundle H48 as the descender post H544 is pushed more
firmly against the rib H46. Thus, further force (or travel) of the
descender post H544 against the rib H46 is born by the sharp points
H560 and H562 loaded into hard, resistant bone, and not just the
tabs H556 and H558, thereby limiting any pressure exerted by the
tabs against the soft tissues adjacent to the rib H46 and, thus,
protecting the neurovascular bundle H48.
J. Compensating for Retractor Deformation
[0453] Many biological tissues are very rigid. For example, rib
cages are made of rigid bone connected by numerous ligaments,
muscles, and tendons--strong enough to withstand the stresses of
human locomotion or lifting large loads. Thus, the forces required
to deform these tissues during procedures such as sternotomy or
thoracotomy are significant. We have measured forces of up to 500 N
during thoracotomies and 250 N during sternotomies on pigs weighing
50 to 60 kg. Forces on vertebral distractors are also large.
[0454] Retractors, by their very nature, are typically made of
rigid stainless steel to withstand the stresses of forcing open rib
cages. However, retractors deform under load. Deformation of a
typical Finochietto-style retractor (e.g. a Finochietto, see FIG.
2, Burford, Ankeney, or other thoracic retractor) is primarily of
two types--the arms bend and twist. Deformation of the retractor is
more complex, e.g. including bending of the rack of the rack and
pinion.
[0455] FIG. 105A shows the bending of the retractor arms J6, J10 of
a Finochietto-style retractor J2 in the prior art when loaded
during retraction. Retractor J2 has two retractor arms J6 and J10.
Retractor arm J6 is fixed to the rack J8 of a rack-and-pinion drive
J4 that is driven by a manual handle J5. Each retractor arm J6 and
J10 has an attached retractor blade J12 and J14, respectively, that
engages the patient's tissues during retraction. Bending J20 of the
retractor arms J6 and J10 causes the distance J36 between the
retractor blades J12, 114 to decrease, whereas the distance J38
between the retractor arms J6, J10 is not greatly effected.
[0456] FIG. 105B shows twisting of the retractor arms J6, JIO of a
Finochietto-style retractor J2 in the prior art when loaded during
retraction. Retractor blades J12 and J14 push against ribs J30 and
J32, respectively. The force on the retractor blades J12, 114
twists the retractor arms J6, JIO, causing the distance J36 to
decrease.
[0457] We have measured deformations, decreases of J36, of up to 2
em when the retractor blades J12, J14 are first separated 10 em and
then loaded with 500 N; in other words, the retractor blades 112,
J14 are forced together 20% of the separation J36 when loaded with
forces seen in thoracotomies.
[0458] These deformations of the retractor J2 are elastic; the
retractorJ2 deforms like a spring under load. If the load
decreases, the deformation of the retractor J2 decreases, and the
retractor blades 112, 114 move further apart.
[0459] The tissues against which the retractor applies this load
are viscoelastic. Unlike an elastic material, a viscoelastic
material will continue to deform when loaded, even if the load is
constant--it will exhibit creep.
[0460] This combination of an elastically deformed retractor J2
pushing against a viscoelastic material creates a problem. Consider
a sternotomy, a surgeon retracts (first phase of retraction) to a
desired opening of the incision and then stops (second phase of
retraction), striving not to retract wider than necessary to reduce
damage to the tissues of the chest. Many retractors are
self-locking or have a lock mechanism designed to hold the incision
at that desired opening during the second phase of retraction.
However, the retractor J2 has deformed during the first phase of
retraction, and now the elastic deformation of the retractor J2
continues to push against the viscoelastic materials of the chest
during the second phase of retraction, causing the thoracic opening
to further widen as the viscoelastic materials of the chest wall
creep under the elastic force of the retractor. This results in an
unnecessarily wide thoracic opening, increasing damage to the
tissues of the chest wall. For example, cardiothoracic surgeons
report that they will hear a "pop" or "snap" as a rib breaks,
sometimes minutes after cessation of the first phase of
retraction.
[0461] This problem is encountered whenever any surgical instrument
or medical device is used to deform a biological tissue because
biological tissues are viscoelastic. Examples include, but are not
limited to, retraction of skin for access to subdermal tissues,
distraction of vertebrae for surgeries on intervertebral discs or
to manipulate vertebrae for fusion or for other fixation,
separation of joints for surgery on cartilage or for joint
replacement, forcing open an annulus or tube with an inflatable
device, such as angioplasty, or any other procedure requiring
deformation of a biological tissue.
[0462] We disclose apparatus and methods for deforming a patient's
tissues to the degree defined by the physician, reducing any
further deformation of the tissue after the desired deformation is
attained, and, thereby, reducing the chances of unnecessary tissue
trauma.
[0463] One solution to this problem is to make the retractor
exceedingly rigid through the use of materials having large Young's
modulus (e.g., titanium which is expensive) or by the use of
members having large cross-sectional area (e.g., wide, thick
members which adds weight to the retractor). This retractor will
still deform elastically, but the elastic deformation of the
retractor will be small, so it will impose only a short distance of
creep on the tissues of the chest.
[0464] An alternative solution is a thoracic retractor that deforms
elastically but the surgical opening is controlled by a
servo-mechanism that maintains the opening at the point set by the
surgeon. Thus, as the tissue begins to creep, causing the retractor
blades to move apart elastically, the servo-mechanism causes the
retractor to close slightly, thereby decreasing the elastic
deformation of the retractor and applying only the force required
to maintain the surgical opening at the point set by the
surgeon.
[0465] FIG. 106 shows one embodiment in which the servo-mechanism
controls the distance J36 between the retractor blades 112, 114 of
a retractor J40. The servo-mechanism is comprised of a motor J44
that opens the retractor J40, a distance measuring device J41 that
measures the surgical opening (e.g. a linear potentiometer), and a
servo-controller J46 that receives the signal from the distance
measuring device J41 and then adjusts the position of motor J44 to
maintain the desired surgical opening, even as the tissue creeps.
Any actuator that effects the deformation of the tissue (i.e. that
powers the first phase of the retraction) can be used; thus, for
the embodiment shown in FIG. 106, the actuator that opens the
retractor J40 is also the actuator controlled by the
servo-controller J44.
[0466] An alternative to direct measurement of the surgical opening
for servo-control, as shown in FIG. 106, is to use the
force-deformation relationship of the retractor (e.g. a spring
constant or a force-deformation curve). During use of the
retractor, the force on the retractor is measured with a force
measuring device, and then the deformation of the retractor is
determined from the measured force using the force-deformation
relationship. This has the advantage that no measuring device is
present in or near the surgical opening.
[0467] FIG. 107 presents an algorithm J50 illustrating one way to
implement a servo-mechanism that uses force measurement with a
force-deformation relationship. A surgeon retracts to a desired
opening (block J51) and then activates the servo-mechanism (block
J52). The position of the motor is recorded by the servo-mechanism
(block 352), the force on the retractor is measured (block J52),
and the motor begins to hold position (block J54). Force is then
measured continuously (block J56). If force remains constant, then
the motor continues to hold position (decision at block J57 then to
step J58). If force decreases (due to creep of the biological
tissue) (block J57 then to step J59), then a translator (e.g. an
electrical circuit, possibly including a microprocessor) uses the
force-deformation relationship to convert the change in force on
the retractor into a change in deformation of the retractor (block
360). The translator then instructs the motor to move to correct
for the change in deformation, thereby keeping the surgical opening
at the separation set by the surgeon (block J62) returning the
feedback loop to block J54.
[0468] A similar algorithm can be used to correct for deformation
throughout retraction. Thus, rather than correct for changes in
deformation on entering the second phase of retraction, the
algorithm can correct for deformation throughout both the first and
second phases of retraction. With such an algorithm, the separation
achieved by the retractor blades (i.e., distance J36) will then
match the separation seen by the surgeon when looking at the
retractor arms (i.e., distance J38). This algorithm also can be
part of an automated retraction system to ensure that separations
J36 intended by the automatic retraction system are, in fact, the
separations achieved.
[0469] FIG. 108 shows a retractor J70 that can control the distance
J36 between the retractor blades J73, J77 by using servo-loop J78
that implements an algorithm such as algorithm J50. The retractor
has a first retractor arm J72 and a second retractor arm J76 that
is driven relative to the first retractor arm J72 by a motorized
rack-and-pinion drive J78 comprised of a rack J74 attached to the
first retractor arm J72 and a drive housing J80 attached to the
second retractor arm J76. Retractor arms J72 and J76 have retractor
blades 373 and J77, respectively. The drive housing J80 houses a
servo-motor J84 and a servo-controller J86 that controls the
servo-motor J84. The surgeon opens the retractor J70 by providing
instructions to the servo-controller J86, for example with a
rotating knob 388 that replaces the crank of a manual
rack-and-pinion. A force measuring device J90, for example a strain
gauge, is placed on the second retractor arm J76 to measure force
on the retractor J70. A translator J82 in the drive housing J80
receives signals from the force measuring device J90 and implements
the algorithm J50. Placement of the force measuring device and the
translator can be at any of several locations, such as on the fixed
retractor arm, but placement of all three components servo-motor,
translator, and force measuring device, on the moveable retractor
arm simplifies the design.
[0470] FIG. 109 shows another retractor J100 that uses two
actuators, a first actuator J101 to drive the first phase of
retraction and a second actuator J108 to adjust for changes in
deformation arising from creep in the tissues during the second
phase of retraction. During the first phase of retraction the first
actuator 1101, a hand-cranked rack-and-pinion in this example, is
used to by the surgeon. A second actuator J108 attached to one arm
of the retractor J100, for example the first arm of the retractor
J6, is controlled by a servo-mechanism J110 and is used to correct
for changes in the deformation of the retractor J100 due to creep
of the tissue during the second phase of retraction. A force
measuring device J102, for example a strain gauge, measures force
on the first retractor arm J6. A translator J104 detects changes in
force, translates these to changes in the deformation of the
retractor 3100, and signals the servo-controller J106 to instruct
the second actuator J108 to move and thereby remove the change in
the surgical opening resulting from the change in the deformation
of the retractor J100. The second actuator J108 can be a
servo-motor, a voice coil, a hydraulic cylinder from which fluid is
released to move the retractor blade J12, or any other actuator
that can move the retractor blade J12 such that the retractor blade
J12 moves closer to the opposing retractor blade J14 when a
decrease in force on the retractor is detected by the translator.
Such a device as shown in FIG. 109 can either be integrated into a
retractor or be a component that attaches to an existing
retractor.
K. A Thoracic Retractor Combining Elements of the Earlier
Sections
[0471] FIGS. 110 through 114 present a thoracic retractor K2 used
for thoracotomies. This thoracic retractor K2 combines components
disclosed in earlier sections. Thoracic retractor K2 comprises two
opposing retractor arms K4 and K6 attached to retraction driver
K60.
[0472] FIG. 111 shows retraction driver K60. Retraction driver K60
comprises a motor-driven rack-and-pinion, with the pinion driven by
a servo-motor K40 controlled by servo-controller K42 and powered by
battery K44. Processor K46 receives input from strain gauge sensors
K14 and K18 that measure the forces on the retractor arms K6 and
K4, respectively. Strain gauge sensors K14 and K18 can be single
gauges or multiple gauges located in multiple locations and arrayed
in, for example, a full bridge configuration; additionally, strain
gauge sensors K14 and K18 can be mounted where the strains in the
underlying material are expected or designed to be large to
increase the sensitivity of force measurement. Processor K46 is in
communication with servo-controller K42 for automatic control of
the servo-motor K40. Retractor arm K4 attaches to the rack K8
connector K5 via and then rotatable mount K16. Retractor arm K6
attaches to driver housing KIO via connector K7. The attachment of
retractor arms K4 and K6 to connectors K5 and K7, respectively, is
secured with fasteners K12. Examples of fasteners include screws,
clips, or any other appropriate mechanical fastener.
[0473] FIG. 112 shows retractor an assembly K50 that attaches via
retractor arm K4 to connector K5 to rotatable mount K16. A similar
retractor arm assembly is attached via retractor arm K6 to driver
housing K10. Retractor arm assembly K50 comprises retractor arm K4
which attaches to balance arm K20 via rotating mount K24; two
daughter balance arms K26 which attach to balance arm K20 via
rotating mounts K30; and two descender posts K52 each with hook K54
attaching to each daughter balance arm K26 via rotatable mount K34.
Thus there are four descender posts K52 each with hook K54. Each
descender post K52 is attached to the daughter balance arm K26 by
rotatable mount K36 such that hook K54 rotates as shown in K56.
Rotatable mount K36 can include a heavy sleeve K34 that reinforces
the joint.
[0474] FIG. 113 shows an enlarged view of rotatable mount K16 which
provides retractor arm assembly K50 an additional degree of
rotational freedom, as disclosed in Section G. Rotatable mount K16
comprises rod K62 that is rigidly coupled to rack K8. Sleeve K64 is
attached to rod K62 and secured by an E-clip (not shown). Rotatable
mount K16, therefore, provides for rotation K66 of retractor arm
assembly K50.
[0475] FIG. 114 shows the shapes and sequence of attachment of
retractor arm K4 to balance arm K20 and daughter balance arms K26
for retractor arm assembly K50. Rotatable mounts K24 and K30 can be
made by connector pins; alternatively, rotatable bushings or
bearings can be used. Rotatable mounts K24 and K30 can be made
loose to provide some freedom of alignment out of the plane of the
page of FIG. 114.
[0476] Connectors K5 and K7 can be replaced by appropriate
snap-together fittings permitting the retractor arms K4 and K6 to
be easily attached and removed. Furthermore, connectors K5 and K7
can include electrical connectors for transmission of power or
electrical signals to electrical components on or connected to the
retractor arms K4 and K6 or to different retractor arm assemblies
K50. Such electrical components can include sensors, processors,
motors or other actuators, data input interfaces, data or status
indicators, or other advantageous electrical components.
[0477] Retractor assembly K50 is designed to distribute the forces
along a rib during a thoracotomy. Other retractor assemblies
designed for other procedures, such as a sternotomy, can be
attached to rack K8 and to retraction driver K60, optionally with
rotating mount K16a replaced by a rigid connection or other
moveable mount.
[0478] Retractor arm assembly K50 can be a disposable component.
Retractor arm assembly can include the battery K44, and if K50 is a
disposable component, this would permit the attachment of a fresh
battery for every use.
[0479] Instructions to the servo-controller K42 and processor K46
can be via a user interface that is integral to retraction driver
K60. An example of a user interface is shown in FIG. 115. The
interface can include a panel in which membrane buttons activate
functions such as start retraction K72, pause retraction K74, fast
forward or accelerate retraction K76, emergency open K78, rewind or
reverse retraction K80, fully close the retractor K82, set duration
for retraction K84, set distance of retraction K86, and a display
K80 for showing information to the user, for example retraction
progress with a progress bar, force on the retractor, or other
information.
[0480] The thoracic retractor K2 shown in FIG. 110 has been
constructed to demonstrate selected embodiments described above
and, specifically, to demonstrate functioning of the self-balancing
retractor arms as described in Section F (e.g., see FIG. 55), the
rotating retraction arm and retraction assembly as described in
Section G (e.g. see FIG. 74), hook-shaped tissue engagers as
described in Section H (e.g. FIG. 98), and automated retraction
with detection of trauma as described in Section C (e.g. algorithm
C300 in FIG. 42). Motor K40 is a model EC22 SOW from Maxon
Precision Motor Inc. The prototype does not have battery K44 or
servo-controller K42 or processor K46 housed in driver housing K10.
Rather, these functions are provided by an off-board power supply
(16V, 4.5 .ANG.), servo-controller (EPOS 24/5 motor controller from
Maxon Precision Motor, Inc), and computer connected by a cable.
Strain gauges from Vishay Micro-Measurements, Inc. are placed at
locations K14 and K18, arranged as full bridges, to measure forces
on arms K6 and K4, respectively. Power to and signals from these
strain gauges is provided by signal conditioners (Model OM-2-115
from 1-800-LoadCell), which then send signals to a data acquisition
card (Model USB-6211 from National Instruments, Inc.) attached to a
laptop computer. Custom software for motor control and data
acquisition is written in LabVIEW from National Instruments,
Inc.
[0481] FIGS. 116A and 116B show retractions from two thoracotomies.
These are fully automated retractions. The surgeon placed the
retractor into the incision, rotated the hooks K54 on the descender
posts K52 under the ribs, and then a remote operator initiated
computer-controlled retraction the computer controlled the rest of
the retraction. The retraction trajectory was programmed to be
parabolic (distance as a function of time, retraction speed
initially higher, continuously decreasing throughout retraction,
and approaching zero speed as full retraction is approached). The
algorithm C300 described in FIG. 42 was used to automatically pause
the retractor, thereby acting as a detector and automatic response
to imminent tissue trauma. If a pause was triggered, then after the
pause, the computer calculated a new parabolic trajectory starting
at the current position and reaching the desired end point; for
example, consider the retraction in FIG. 116B: [0482] the desired
endpoint was 62 mm; [0483] retraction was to occur over 45 seconds;
[0484] a pause occurred at 43 mm after 20 seconds had elapsed, with
the pause being 20 seconds long; thus [0485] the remaining
retraction distance (62 43=19 mm) was to be covered in (45 20
-20)=5 seconds.
[0486] Alternate algorithms for desired endpoints, desired
retraction duration, pause durations, and means of recalculating
the trajectory after the pause can be used. Alternate algorithms
could be: [0487] e Desired endpoint=50 mm; desired retraction
duration 50 s; pause duration=15 s; if pause occurs in last 30 s of
retraction, then set the pause duration to be equal to half the
remaining time; or [0488] Desired endpoint 100 mm; desired
retraction duration=2 minutes (120 seconds); pause
duration=one-third of time remaining at the initiation of a pause.
The complexity of the algorithm is limited only by such things as
the processing power of the processor K46, the numbers and types of
sensors used, etc.
[0489] FIG. 116A shows the displacement K100 and forces on the
right arm K102 and left arm K104 for a retraction to 50 mm over
about 35 seconds. This retraction should be compared to a similar
retraction performed with an instrumented Finochietto retractor
(shown in FIG. 37) for retraction to 52 mm over about 50 seconds.
Both retractions in FIGS. 37 and 116A were performed on the same
animal. The retraction in FIG. 37 was at rib pair 4/5 on the left
side, and the retraction in FIG. 116A was at rib pair 4/5 on the
right side. Returning to FIG. 116A, retraction starts K106 at 2
seconds and follows a substantially parabolic trajectory, with
retraction ending at K108. We have found that such substantially
parabolic trajectories have less evidence of tissue trauma than
other trajectories, such as linear trajectories or, as in FIG. 37,
stepped trajectories. It is important to note several things:
[0490] (1) No pause was triggered. [0491] (2) The maximum force
generated during retraction was about 300 N, about 25% less than
the 400 N observed with the instrumented Finochietto during
retraction to 52 mm over 50 seconds (FIG. 37). This lower force of
retraction is especially noteworthy because the more rapid
retraction in FIG. 116A should have required more force than the
slower retraction in FIG. 37. [0492] (3) The forces on the two
retractor arms are nearly equal, unlike the unequal forces seen on
the retractor arms in FIG. 37. [0493] (4) The force traces K102 and
K104 in FIG. 116A are exceedingly smooth, unlike the extremely
jagged traces seen in FIG. 37. Note that all the data presented in
FIGS. 116 and 117 are raw data--the data are not smoothed, the
traces are not fitted curves.
[0494] FIG. 116B shows another retraction with retractor K2. This
retraction was at rib pair 5/6, right hand side, of the same animal
as in FIGS. 37 and 116A. We performed multiple retractions on this
rib pair, going to increasingly wider endpoints, in an attempt to
get a pause to be initiated by the algorithm C300. FIG. 116B shows
the third retraction which was to an endpoint of 62 mm over 45
seconds. Retraction started at K110 and ended at Kill. A pause K112
was triggered by a negative-going spike (too small to see in this
figure) at the point marked by the arrow K113 approximately 20
seconds after starting retraction. Retraction before the pause
produced a very smooth displacement trace K114 and force traces
(right and left arms collectively labeled K118). Only a small
amount of force relaxation is evident in the pause. The retraction
after the pause was very rapid, due to the short time allowed by
the algorithm (about 5 seconds), but again produced a very smooth
displacement trace K116 and force traces, right and left arms
collectively numbered as K120.
[0495] It is noteworthy that the forces on the retractor relaxed
only slightly during the pause in FIG. 116B and also at the end of
the retractions in both FIGS. 116A and 116B, relative to the
relaxation seen after each liz-rotation of the crank in FIG. 37.
This indicates that slow, steady pulling permits force relaxation
to occur simultaneously with retraction and, therefore, also
indicates that there is an optimum retraction speed that maximizes
force relaxation and thereby reduces forces during retraction. A
substantially parabolic trajectory, as described above, provides
such an optimal retraction.
[0496] FIGS. 117A, 117B, and 117C present the same data from the
retractions shown in FIGS. 116A and 116B, but show only force for
the left retractor arm; these figures also show the second
derivative of the force, d.sup.2F/dt.sup.2, referred to here as the
Fracture Predicting Signal, FPS, where fracture can be of any
tissue (e.g. rib, ligament, tendon, muscle) giving rise to tissue
trauma.
[0497] FIG. 117A shows the retraction from FIG. 116A. Traces for
both the FPS K130 and force K104 on the left retractor arm are
presented. The FPS trace K130 is constant, with low noise, at zero
throughout the retraction. There are no negative-going spikes and
no increase in variance of the signal that would trigger a pause,
so there was no pause in this retraction.
[0498] FIG. 117B shows the retraction from FIG. 116B. The force
trace K132 is presented from the left retractor arm only. Here,
there is a prominent event K134 at about 24 seconds that triggers
the pause K112.
[0499] FIG. 117C shows the event K134 with an expanded scale. A
small drop in the force K132 occurs in event K134, a decrease of
only about 3N (1% of the maximum retraction force during this
retraction). This creates a negative going spike K136 in the FPS
K130 that triggers the pause. Retraction stopped 0.2 seconds after
the drop in force K132 (displacement trace not shown).
[0500] Returning to FIG. 117B, there is another event K140 in the
FPS during retraction after the pause. This event was not
sufficient to trigger a second pause, and retraction proceeded to
completion Kill.
M. Detecting Tissue Trauma During Retraction
[0501] Balloon angioplasty is a widely used medical procedure for
opening atherosclerotic plaques in blood vessels throughout the
body, including vessels of the heart, the legs, and the neck.
Similar procedures are balloon valvuloplasty, which is used to open
or otherwise reshape valves of the heart, and other techniques for
opening circular or cylindrical tubes or apertures in the body
(e.g. the gastrointestinal and respiratory paths).
[0502] In balloon angioplasty, a balloon is attached at or near the
end of a catheter, with the catheter being a long, narrow tube
(e.g. 3 mm diameter and 1 meter long) (see FIG. 118). The balloon
M1OO is introduced into the circulatory system (commonly through an
incision into a vessel of the leg) and advanced to the plaque M110
by pushing catheter M120 (FIG. 118A). The balloon M100 is then
inflated by pushing fluid through the catheter M120 into the
balloon M1OO (FIG. 118B), typically with a syringe or other
displacement pump. Inflation of the balloon M1OO forces open the
plaque MilO, restoring a more normal inner diameter to the vessel
(FIG. 118C). Frequently, a metal stent is then placed in the vessel
to hold the vessel open, blocking re-stenosis of the vessel. The
balloon MIOO is then deflated by removing fluid through the
catheter M120, and the balloon M1OO is removed with withdrawal of
the catheter M120.
[0503] Inflation of an angioplasty balloon, or other balloons for
other similar procedures, is a forceful distension of a biological
tissue that irreversibly deforms that tissue. Inflation pressures
are often in the range of 8 to 10 atmospheres (ATM, 120 to 150
p.s.i.) and can be much greater (Freynet and Falcoz 2010).
[0504] The degree of inflation of the balloon is, in part,
determined by the compliance of the balloon, defined operationally
as the pressure/volume relationship of the balloon. Thus, for
example, a FX MiniRAIL balloon (model FX20XX, Abbot Vascular, Santa
Clara, Calif., USA) has a diameter of 1.62 mm at 2.0 ATM, 1.76 mm
at 4.0 ATM, 1.87 mm at 6.0 ATM, 2.04 mm at 10.0 ATM and a Rated
Burst Pressure of 14.0 ATM. However, the actual inflation of the
balloon is determined also by the hardness of the plaque--the
inflation pressure may not be sufficient to deform the plaque and,
thus, the balloon may be restricted at less than the diameter
predicted by the balloon's compliance. The actual diameter of the
balloon is observed by the surgeon using medical imaging
technologies, such as fluoroscopy.
[0505] Inflation of the balloon is frequently performed in steps.
For example, instructions for the FX MiniRAIL balloon (Abbot
Vascular, Santa Clara, Calif., USA) recommends the following
inflation sequence: [0506] a. Begin by increasing the pressure to 2
ATM and remaining at this pressure for 20 seconds. [0507] b.
Increase the pressure in steps, increasing the pressure 1 ATM every
20 seconds until the balloon appears inflated under visual
observation by fluoroscopy. Typically, the balloon will appear
indented by the plaque, and this indentation in the balloon
disappears. This pressure is called the "Stenosis Resolution
Pressure" or SRP. Hold at this pressure for 10 seconds. [0508] c.
After SRP is achieved, increase the pressure at a rate of 1 ATM
every 10 seconds until the target balloon diameter is achieved as
determined visually by fluoroscopy. Hold this final pressure for 20
seconds. [0509] d. Never exceed the Rated Burst Pressure of the
balloon.
[0510] Other components of the angioplasty fluidic system are
compliant. The catheter, the syringe, and other components are
frequently composed of semi-rigid polymers. For example, common
catheter materials are polyvinyl chloride (PVC), polyethylene (PE),
polyolefin copolymer (POC), or polyethylene terephthalate (PET).
Syringes are commonly composed of polypropylene (PP) with
elastomeric stoppers.
[0511] All of these components of the angioplasty fluidic system
deform at the pressures used to inflate balloons. This can create
several unintended or undesired results. For example, if a plaque
is particularly hard to distend, pressure can build in the fluidic
system without expansion of the balloon. The other components of
the fluidic system, if compliant or non-rigid, do, however,
distend. This creates a pressure-volume reservoir (PVR) in the
fluidic system. If the surgeon increases the pressure only slightly
more, and then the plaque begins to yield, the PVR in the fluidic
system will drive sudden inflation of the balloon, not an
incremental inflation. This inflation is sudden because the stress
to deform the vessel wall decreases as it begins to deform (i.e.
once yield stress is reached, further deformation is driven by
lower stresses), thus the PVR in the fluidic system will rapidly
push fluid into the balloon which is now no longer constrained by
the plaque.
[0512] Rapid expansion of the balloon means that materials in the
plaque and vessel wall experience high strain rates. High strain
rates can result in larger trauma to biological tissues than lower
strain rates because biological tissues are viscoelastic, composite
materials having hierarchical composition and, in the case of
plaques, highly unevenly distributed materials with disparate
mechanical properties.
[0513] Control of flow in the fluidic system is further confounded
by the use of polymeric materials that are not only compliant, but
also viscoelastic. Thus, when a polymeric component is distended by
pressure and then that pressure is reduced, the PVR in the
component will drive flow out of the component, but with a long
time response as the viscoelastic component only recovers its
original volume with time.
[0514] Balloon angioplasty significantly increases the diameter of
the obstructed vessel (e.g. from nearly closed to 3 to 5 mm).
Deformation of the tissue, therefore, almost always exceeds
physiological ranges of a few percent strain and, thus, results in
tearing or other damage of the tissue. Cracks in the plaque,
delamination of the plaque, and dissection of the vessel wall are
all known to occur (Honye, Mahon et al. 1992). All can be
problematic. For example, dissection of the wall of a coronary
artery can rupture the vessel, requiring emergency surgery for
repair.
[0515] A less traumatic means for deforming tissues with a balloon
is desired.
M.1 Controlling Compliance Flow to Reduce Trauma to Tissues
[0516] A non-compliant fluidic system M200 is shown in FIG. 119.
Balloon M201 is mounted onto catheter M210. Catheter M210 is
attached to syringe M220 by fitting M230. Syringe M220 has plunger
M240 that pushes fluid M250 out of the syringe into the catheter
M210 into balloon M201. Syringe M220 and plunger M240 are made of
non-compliant materials, such as glass and steel, with the seal of
the plunger formed by a thin 0-ring of rigid material M260, such as
Teflon. Similarly, the entire plunger M240 can be made of Teflon.
Fitting M230 permits attachment/removal of catheter M210 from
syringe M220. Note that non-compliance of the system obviates
problems otherwise created by viscoelasticity of these components
because a non-compliant component does not distend.
[0517] Appropriate non-compliant syringes and plungers can include
those developed for high-pressure injection systems for
high-pressure liquid chromatography (HPLC) systems, such as the
1700 Series GASTIGHT syringe (10 microliter (.mu.L) to 500
microliter (.mu.L) volume) and the 1000 Series GASTIGHT syringe
(100 microliter (.mu.L) to 100 microliter (.mu.L)) from the
Hamilton Company (Reno, Nev., USA). Similarly, fittings used for
HPLC can be used in a non-compliant fluidic system for angioplasty,
such as for fitting M230.
[0518] Non-compliant catheters can be composed of more rigid
polymers, such as polyetheretherketone (PEEK), glass filled PEEK,
carbon filled PEEK, and from non-polymeric material such as fused
silica. Examples of fused silica include capillaries from Polymicro
Technologies (Phoenix, Ariz.). Fused silica capillaries can be
coated with polyimide or other polymers to make the capillaries
more resistant to fracture, such as the fused silica capillaries
available from Polymicro Technologies (Phoenix, Ariz.).
[0519] FIG. 120 depicts another non-compliant fluidic system M300
that is similar to non-compliant fluidic system M200, except that
non-compliant fluidic system M300 has a pressure gauge M310
connected to fluidic connector M320 by non-compliant tube M330 such
that pressure gauge M310 reports the fluid pressure of fluid M250
inside non-compliant fluidic system M300. Fluid displacement from
syringe M220 into catheter M210 can be determined by measuring the
travel of plunger M240 and multiplying by the cross-sectional area
of syringe M220. Non-compliant fluidic system M300 permits the
simultaneous measurement of both pressure and fluid displacement
during inflation of balloon M201.
[0520] FIG. 121 depicts another non-compliant fluidic system M400
that includes a switching valve M410 that connects to fluid vial
M420 to permit refilling of the non-compliant fluidic system M400
with fluid M250 or, optionally, with a second fluid M430. FIG. 121
depicts non-compliant fluidic system M400 configured to inject
fluid into catheter M210. FIG. 122 depicts non-compliant fluidic
system M400 with switching valve M410 switched to pull fluid M430
from fluid vial M420 into syringe M220 by pulling plunger M240 in
the direction of arrow M450. Examples of switching valve M410
includes switching valves for high pressure liquid chromatography
(HPLC) from manufacturers such as Valco Instrument Company
(Houston, Tex.) and the Waters Company (Milford, Mass.). Switching
valve M410 can, optionally, be motorized and controlled by external
electronic switching (not shown) for remote actuation of switching
valve M410, as is common for HPLC switching valves.
[0521] The switching valve can also be a manually switched or
motor-driven stopcock fabricated from materials that are
sufficiently stiff that they can create a non-compliant fluidic
system. For example, a stopcock fabricated from glass either having
precision ground seals or having Teflon seals could be used; or a
stopcock fabricated from stainless steel and having Teflon seals
could be used. Additionally, all components of the non-compliant
fluidic system, exclusive of the balloon or catheter can be
fabricated such that it is readily sterilized using conventional
sterilization methods (e.g. steam autoclaving or ETO gas). This
permits the entire system to be sterilized for re-use within a
normal hospital setting.
[0522] FIG. 123 depicts a catheter M500 that is comprised of an
external sheathing material M510 surrounding multiple smaller tubes
M520. The outside of catheter M500, therefore, can be composed of
materials that are commonly used in angioplasty catheters, such as
polyvinyl chloride (PVC), polyethylene (PE), polyolefin copolymer
(POC), or polyethylene terephthalate (PET), while the smaller tubes
M520 are composed of non-compliant materials. The smaller tubes
M520 are composed of non-compliant materials, such as fused silica
capillaries, such as those from capillaries from Polymicro, Inc.
(Phoenix, Ariz.). Fused silica capillaries can be coated with
polyimide or other polymers to make the capillaries more resistant
to fracture, such as the fused silica capillaries available from
Polymicro, Inc. (Phoenix, Ariz.). There can be more or fewer
smaller tubes M520 than depicted. The multiple smaller tubes M520
can be used to conduct a fluid in a non-compliant fluidic system.
The use of smaller tubes M520 permits the use of fused silica
capillaries that are more flexible and less likely to fracture
because larger fused silica capillaries are stiffer. The use of
multiple tubes helps offset the fluidic resistance experienced in
smaller tubes. Conversely, multiple tubes can be used to conduct
different fluids along catheter M500, similar to multiple-lumen
catheters from manufacturers like Zeus (Gaston, S.C.).
[0523] FIG. 124 depicts a catheter M550 similar to catheter M500;
however, catheter M550 also includes wires M530. There can be more
or fewer wires M530 than depicted. Wires M530 can be bare wires,
insulated wires, multiple conductor wires, or shielded cables.
[0524] FIG. 125 depicts how smaller tubes M520 and wires M530 can
be enclosed in sheathing material M510 of catheter M600, and by
similar method of catheter M500 and M550, such that the internal
lumen M610 of catheter M550 is sealed while still permitting
smaller tubes M520 and wires M530 to emit from catheter M550.
Potting material M620 forms a fluid-tight seal at the end of
catheter M550, encapsulating smaller tubes M520 and wires M530.
This method of forming a fluid-tight seal permits the attachment of
all smaller tubes M520 to a common pressure source. Potting
material M620 can include epoxies, plastics, and other materials
providing mechanical and chemical properties appropriate to the
application. Lumen M610 can be filled with a sterile liquid,
including lubricants to reduce friction between the smaller tubes
M520 and wires M530.
[0525] FIG. 126 depicts how smaller tubes M520 and wires M530 of
catheter M700 can connect to separate components in a larger
fluidic system. Multiple syringe assemblies M710, M720, M730 are
connected to a 6-port switching valve M750 to which smaller tubes
M520 are connected. Wires M530 are connected to an electrical board
M760. This assembly permits the delivery of multiple types of
fluid, a different fluid into each catheter, or of one type of
fluid delivered independently into each catheter. Wires M530
connect to electrical board M760, permitting electrical
communication with electrical components on the other end of
catheter assembly M700. Changing 6-port switching valve M750 to its
alternated position switches the syringe assembly attached to a
smaller tube, thereby permitting the sequential introduction of
different fluids into a smaller tube, if desired. Note that the
6-port switching valve M750 and syringes M710, M720, and M730 are
used as an example only. Any separate pressurized fluidic sources
can be used. Additionally, pressure gauges can be attached to any
or all fluidic assemblies.
[0526] FIG. 127 depicts how a pressure gauge M810 can be placed
inside the balloon M820 of an angioplasty balloon assembly M800.
This placement of pressure gauge M810 enables direct measurement of
pressure inside the balloon M820. Wire M530 and smaller tubes M520
reside inside catheter sheathing material M510, and potting
material M620 forms a seal separating balloon M820 from the lumen
M610 of the catheter. Thus, smaller tubes M520 permit inflation of
balloon M820 by a non-compliant fluid system such as shown in FIGS.
120, 121, 122, and 126.
[0527] FIG. 128 shows an assembly M900 whereby a first smaller tube
M910 emits from the end of the assembly M900 while a second smaller
tube M920 inflates the balloon M930. Pressure gauge M810 is
connected to wire M530 and measures pressure inside balloon M930.
Smaller tube M920 connects to a fluid/pressure source that inflates
the balloon M930. Smaller tube M910 connects to a second
fluid/pressure source, such as a syringe assembly, for delivering a
second fluid downstream of the balloon M930. Examples of such a
second fluid include contrast medium or fluid containing oxygen,
nutrients, or drugs for treatment of the blood vessel downstream of
the balloon M930, especially after inflation of balloon M930.
Similarly, a smaller tube can emit upstream of the balloon, or
multiple smaller tubes can be used to deliver fluid to both sides
of the balloon or to multiple points.
[0528] FIG. 129 shows a non-compliant fluidic system M1000 for
inflating an angioplasty balloon M1010 with a precisely controlled
pressure and volume of inflation while also delivering a second
fluid downstream of angioplasty balloon M1010. Balloon is attached
to catheter M1020 which contains wire M1030 connecting pressure
gauge M1040 to electrical board M1050. Smaller tube M1100 passes
through potting material M1110 and inflates balloon M1010 with a
first fluid M1120 which is pushed by syringe assembly M1130 which
is driven by syringe pump M1140. Smaller tube M1200 passes through
potting material MillO and balloon M1010 to deliver a second fluid
M1210 downstream of the balloon M1010. Second fluid M1210 is pushed
by syringe assembly M1220 which is driven by syringe pump M1230.
Switching valve M1240 alternately connects syringe assembly M1220
to smaller tube M1200 (to deliver fluid M1210 downstream of the
balloon M1010) or to vial M1250 to permit refilling of syringe
assembly M1220. Switching valve M1240 is actuated by stepper motor
M1260. This system allows an operator to simultaneously monitor
fluid flow rates from syringe assemblies M1130 and M1220 and
pressure inside balloon M1010. It also permits refilling of syringe
assembly M1220 with fluid M1210 without disconnecting syringe
assembly M1220, streamlining operation and eliminating risks of
contamination of sterile components and of operator error during
refill.
[0529] Non-compliant fluidic system M1000 can be automated by
attaching a computer to electrical board M1050 for automated
measurement of pressure inside the balloon M1010; syringe pump
M1140 for automated delivery of fluid M1120 to inflate balloon
M1010; and syringe pump M1230 and stepper motor M1260 for automated
delivery of fluid M1210 downstream of balloon M1010 and for
automated refill of syringe assembly M1220. Thus, automated system
MIOOO is capable of controlling all aspects of the inflation of
balloon M1010 and delivery of fluid M1210 downstream of balloon
M1010.
[0530] Automation of non-compliant fluidic system M1000 permits a
further reduction in the chance of operator error during all
aspects of operation of the system. It also enables precise
comparison of the pressure-volume relationship of balloon MIOIO.
Pressure is measured by pressure gauge M1040, and volume is
measured by the fluid displaced by syringe assembly M1130 driven by
syringe pump M1140 (i.e. diameter of the syringe barrel times the
distance of displacement of the syringe plunger equals the
displaced volume). For example: [0531] a. If the pressure inside
balloon M1010 rises faster than predicted by the compliance of the
balloon M1010 as fluid M1120 is pumped into balloon M1010, then the
plaque or other anatomy is resisting inflation of the balloon
M1010. If pressure should start to fall, even while syringe
assembly M1130 is stopped or is pushing fluid M1120 into balloon
M1010, then either the plaque has started to yield or the balloon
M1010 has ruptured. These two alternatives can be distinguished
from one another by halting syringe assembly M1130 and measuring
pressure inside balloon M1010 with pressure gauge M1040. If
pressure continues to decline toward zero, then the balloon has
most likely ruptured. This can be further validated by slowly
pushing fluid 1120 with syringe assembly M1130 into balloon
M1010--if pressure fails to rise, or the volume exceeds that
expected for the measured pressure then the balloon M1010 has
ruptured; if pressure rises, but stays within the expected
compliance of the balloon M1010, then the plaque has yielded.
[0532] b. If pressure inside the balloon M1010 suddenly decreases,
but does not drop to zero, then a component of the vessel wall has
failed. To avoid further damage to the vessel, inflation can be
paused to permit stress relaxation in the tissues of the
plaque/vessel. Pressure is defined as force per unit area at the
surface of the balloon; thus, by substituting pressure for force,
any of the techniques for detecting tissue trauma by monitoring
changes in force that are disclosed in Section C--Detecting Tissue
Trauma During Retraction can be applied. For example, pressure can
be monitored while fluid M1120 is slowly and steadily (e.g.
constant volumetric flow rate, or known profile of volumetric flow
rate over time, or simply a smoothly varying volumetric flow rate)
pumped into balloon 1010.
[0533] FIG. 130 illustrates how pressure and the slope of pressure
(dP/dt) is expected to vary over time if a component of the plaque
fails. (Note that FIG. 130 is not data from an experiment with an
angioplasty balloon, but is presented for illustrative purposes.)
Inflation starts at 30 seconds, and pressure rises smoothly, with
the slope increasing smoothly (ignoring noise in the signal). At
the point marked by an asterisk, the trace of the slope changes
pronouncedly, with the point of transition marked by a large
negative-going spike. At this point, a component of the vessel wall
failed.
[0534] FIG. 131 illustrates how pressure and the second time
derivative of pressure (d.sup.2P/dt.sup.2 is expected to vary over
time if a component of the plaque fails. (Note that FIG. 131 is not
data from an experiment with an angioplasty balloon, but is
presented for illustrative purposes.) Inflation starts at 30
seconds, and pressure rises smoothly. Now the second time
derivative remains constant (ignoring noise) at zero. At the point
marked by an asterisk, the trace of the second time derivative
changes pronouncedly, with the point of transition marked by a
large negative-going spike. At this point, a component of the
vessel wall failed.
[0535] Techniques to detect failure of a component of the vessel
wall are important because continued distension of the vessel wall
by the angioplasty balloon could lead to large fractures of the
vessel wall, perhaps leading to dissection and rupture. To avoid
such extensive damage to the vessel wall, an automated
non-compliant fluidic system M1 000 could automatically and
immediately take measures to either stop further distension or to
reduce damage on further distension. Non-compliant fluidic system
MIO00 could stop syringe pump M1040, ceasing further fluid flow
into balloon M1010. Note that by being non-compliant, fluid flow
into balloon M1010 would cease immediately. (If there was
compliance in the system, then fluid would continue to be pushed
into the balloon.) At this point, the balloon could be deflated and
withdrawn. Alternatively, the balloon could be held at this
inflation to permit stress relaxation in the walls of the vessel
and plaque, decreasing stress concentration at fractures; after a
fixed period of time, having allowed sufficient stress relaxation,
inflation of the balloon can be continued to permit further
distension of the plaque but now with a reduced risk of trauma to
the vessel.
[0536] FIG. 132 depicts an example of an algorithm M1300 for
detecting imminent tissue trauma. The algorithm M1300 can be used
for any pressure profile (inflation over time) with any device that
measures pressure. The algorithm M1300 searches for both a
negative-going spike in the pressure trace and for an increased
variability ("noisier") pressure trace. The user inputs two
thresholds, Ts for detecting the negative-going spike and Tv for
detecting increased variance. The thresholds Ts and Tv allow the
user to set the sensitivity of the algorithm M1300. For example, a
surgeon might choose to use a more sensitive setting for a patient
expected to have a fragile plaque. Variability in the pressure
signal is calculated as the root-mean-square (RMS) of the pressure
trace. Execution of the algorithm M1300 starts (block M1302) at the
initiation of inflation. Inflation proceeds for N+0.1 seconds
(block M1304), with pressure sampled at a rate equal to or greater
than 10 Hz. The algorithm M1300 then calculates RMS of
d.sup.2P/dt.sup.2 over the last N seconds (block M1306), skipping
the first 0.1 second to avoid transients from the start of
inflation (e.g., motor stiction, etc.). The algorithm M1300 first
looks for a negative going spike in d.sup.2P/dt.sup.2 by comparing
the last measurement to the RMS over the last N seconds (RMSN)
multiplied by the threshold Ts input by the user
(d.sup.2P/dt.sup.2<(O-TS* RMSN)) (block M1308). If the pressure
is more negative than this parameter, then a 20 second pause in
inflation (block M1310) is triggered permitting stress relaxation
in the tissues, and the algorithm M1300 returns to the start (block
M1302). If d.sup.2P/dt.sup.2 is not more negative than this
parameter, then the algorithm 1300 checks for increased variability
in d.sup.2P/dt.sup.2 by comparing the RMS over the past 0.5 seconds
(RMS.sub.0.5) to the RMS over the past N seconds (RMSN) multiplied
by the threshold Tv (block M1312). If RMS.sub.0.5 is greater then a
20 second pause (block M1310) in retraction is triggered permitting
stress relaxation in the tissues, and the algorithm M1300 returns
to the start (block M1302). If RMS.sub.0.5 is not greater then
retraction proceeds for another 0.1 second (block M1314) and checks
again (block M1306). Thus, pressure is checked for a negative-going
spike in d.sup.2P/de and for increased variability in d.sup.2P/de
every 0.1 seconds. The pressure trace can be checked more or less
frequently. Other sampling frequencies can be used. The 0.1 second
added toN in block M1304 can be any other time interval sufficient
to avoid transients in the pressure trace on starting the motor or
around any other event deemed spurious to detecting tissue trauma.
The event triggered by the detection algorithm (a 20 second pause
in this case) can be any event that is appropriate to the detected
signal. For example, inflation can pause with continued measurement
of pressure and then inflation can resume after the slope of the
pressure trace becomes shallow, indicating that stress relaxation
has approached a limit. Another example is to initiate an
oscillation of the inflation to accelerate stress relaxation, or to
pause for a first period and then to oscillate for a second
period.
[0537] When measuring pressure inside the angioplasty balloon,
changes in pressure driven by blood pressure can be actively
filtered out either by using an appropriate low-cut or band-cut
digital filter. Alternatively, blood pressure can be measured by
any standard method and subtracted from the signal measured inside
the balloon. Covariance of blood pressure and pressure in the
balloon can, in fact, be used as a diagnostic. For example, before
the balloon has occluded the blood vessel, blood pressure impinges
on the entire balloon surface, contributing a larger component to
the pressure inside the balloon. As the balloon occludes the
vessel, shielding the balloon surface from the bulk of the blood
volume, blood pressure will contribute a smaller component to
pressure inside the balloon. Thus, drop out of blood pressure from
the pressure signal can act as a signal for apposition of the
balloon against the plaque.
[0538] Note that non-compliant fluidic system M1000 need not be
automated. Any signal reflecting a change in pressure, or otherwise
indicating that a change in action by the syringe pumps M1140 or
M1230 is needed, could be performed by an operator. For example, an
indicator light could illuminate when an event occurs, with the
observer taking the appropriate action, e.g. halting syringe pump
M1140.
[0539] As stated above, any other of the techniques for detecting
tissue trauma by monitoring changes in force that are disclosed in
Section C of US Patent Application Number 20090259107 can be
applied. Monitoring sound using a miniaturized sonophone placed
inside the balloon would be a sensitive means for detecting sound
emitted by the plaque during distension, with "snaps" and "pops"
reporting failure of plaque components.
[0540] Measuring devices can be placed in the fluid lines leading
to the balloon, rather than in the balloon. FIG. 133 shows a
non-compliant fluidic system M1400 with pressure gauge M1410
measuring pressure inside smaller tube M1100. Pressure gauge M1410
is connected by wiring M1420 to electrical board M1430. Measuring
pressure at this point in the fluidic system must take into
consideration the pressure difference from the point of measurement
to the balloon M1010. For example, when fluid is being driven by
syringe pump M1140, pressure will be higher at the point measured
by pressure gauge M1410 than inside balloon M1010. This difference
can be readily calculated using the Hagen-Poiseuille equation. (The
radius and length of the smaller tube MllOO is known, and the
volumetric flow rate can be calculated as described earlier.)
Additionally, this pressure difference simply presents a pressure
offset if the volumetric flow rate is constant, and will not have
any effect on the second time derivative of the pressure, making
algorithms (such as that depicted in FIG. 132) readily applicable.
If the volumetric flow rate is not constant but is at least
smoothly varying then, again, the effect on the second time
derivative will be small, making the second time derivative readily
usable.
[0541] FIG. 134 depicts how a 6-port switching valve M1500 can be
used to inject a bolus of fluid into the stream of fluid from a
syringe M1510. This is advantageous when a different fluid needs to
be injected for a limited time or with a known volume into either a
balloon or downstream from the balloon (e.g. a contrast agent or a
drug). FIG. 134 shows a fluidic system in two states, State A and
State B. In State A, a first fluid from syringe M1510 flows into
catheter M1530 that can then flow into either a balloon or a
catheter delivering fluid outside the balloon, either upstream or
downstream of the balloon or to other locations in the vascular
system. A second fluid from syringe M1520 fills injection loop
M1540 by pushing the second fluid through injection loop M1540 and
out to waste; when injection loop M1540 is full, syringe M1520
stops driving the second fluid, and injection loop M1540 then
contains a known volume of the second fluid. (The volume is
determined by the diameter and length of the tube used to form
injection loop 1540.) In State B, 6-port switching valve M1500
moves to another position whereby injection loop M1540 is brought
in-line with syringe M1510 and catheter M1530; thus, syringe M1510
now drives the second fluid in injection loop M1540 into catheter
M1530. Using the system depicted in FIG. 134, delivery of a second
fluid into catheter M1530 can be done without breaking or remaking
any seals, ensuring sterility of the transfer. Furthermore, the
entire operation can be automated by driving 6-port switching valve
with a motor and syringes M1510 and M1520 with syringe pumps. Note,
also, that the system can return to State A, allowing re-filling of
the injection loop with the second fluid and, thus, delivery of a
second bolus of the second fluid, if desired. Other switching
valves can be added to this system to deliver a third fluid (or
more fluids) into catheter M1530.
[0542] FIG. 135 illustrates a catheter M1600 similar to catheter
M500; however, catheter M1600 also includes fiber optics M1610.
There can be more or fewer fiber optics M1610 than depicted.
Optionally, if smaller tubes M520 are fused silica capillaries,
then they can be fiber optic fused silica capillaries, such as the
Light Guiding Flexible Fused Silica Capillary Tubing manufactured
by Polymicro Technologies (Phoenix, Ariz., USA). Both devices,
fiber optics M1610 or fiber optic fused silica capillaries permit
the delivery of light down the catheter to one or more points on
the catheter or balloon or, similarly, the collection of light from
one or more points on the catheter or balloon. Delivery and
collection of light can be used for diagnostic procedures (e.g.
fluorescence, back scattering, etc.) or for therapeutic means (e.g.
photolysis).
[0543] Compliance elsewhere in the fluidic system, as described
above, can drive fluid into an angioplasty balloon or other
inflatable device if the forces restraining the balloon drop, as
would occur when a component fails in the wall of the artery or of
a plaque in the wall of an artery or when the wall of the
angioplasty balloon fails, such as perforating. Such flow into the
angioplasty balloon or other inflatable device, that is driven by
compliance of components of a fluidic system outside the inflatable
device, is herein termed "compliance flow".
[0544] FIG. 136 depicts an alternate embodiment for controlling
compliance flow into an angioplasty balloon or other inflatable
device. A fluidic system M1700 comprises a several components
connected by conduits M5 that convey fluid M250 between components
and includes a balloon which can be generalized as an inflatable
device M1705 with a wall M1710 that is pressed against the
biological tissue, such as the wall M1715 of an artery M1720.
Inflatable device M1705 is connected by a tube M1725 having a
distal end M1727 in fluid communication with inflatable device
M1705 and with a pump M1730 in fluid communication with the
proximal end of tube M1725. Inflatable device M1705 is shown here
in cross-section, with tube M1725 passing through the center of
inflatable device M1705. Lateral holes M1711 in the wall M1710 of
tube M1725 inside inflatable device M1705 permit inflation. Thus
fluid M250 flows down the lumen of tube M1725, out lateral holes
M1711, and into the lumen of inflatable device M1705.
[0545] Pump M1730 drives fluid M250 through fluidic system M1700 to
inflate inflatable device M1705 such the wall M1710 of inflatable
device M1705 presses against the wall M1715 of artery M1720. Pump
M1730 can generate pressure at a constant rate over time or at
variable rates, optionally with computerized control by controller
M1750 via pump signal M1731. Pump M1730 can generate pressure
profiles similar to the force profiles described in Section
A--Constant Force and in Section B-Oscillating Loading to reduce
trauma to the biological tissue.
[0546] Compliance flow control system M1735 acts to reduce
compliance flow if the wall M1715 of artery M1720 should begin to
yield or otherwise break threatening rupture, such as when a fiber
or lamina or other component in the wall M1715 breaks. The
compliance flow control system M1735 rapidly decreases the pressure
at the proximal end of the tube M1725 to limit compliance flow
driven by compliance in the fluidic system M1700 upstream of the
proximal end of tube M1725. The compliance flow control system
M1735 includes one or more measuring devices M1740 that communicate
a control signal(s) M1741 to controller M1750, and a pressure
release device M1745 that receives an activation signal M1746 from
controller M1750 that, on activation, decreases fluid pressure at
the proximal end of tube M1725. Compliance flow driven by
compliance inside the fluidic components of fluidic system upstream
of pressure release device M1745 is thus directed out of fluidic
system M1700 and not into tube M1725 (and thus not into inflatable
device M1705). Additionally, some of the compliance flow driven by
compliance in tube M1725 will also exit fluidic system M1700
through pressure release device M1745, further reducing compliance
flow into inflatable device M1705. The compliance flow control
system M1735 can, optionally, also stop the pump M1730 using pump
signal M1731.
[0547] Fluidic system M1700 thus operates to reduce compliance flow
by first detecting a drop in pressure arising from failure of some
part or all of wall M1715 of the artery M1720 (or of wall M1710 of
inflatable device M1705) or the subsequent compliance flow into
inflatable device M1725 due to this drop in pressure, or both. The
release of pressure can be maintained until the pressure in system
M1700 decreases to a predetermined amount, such as to zero pressure
or to some pressure greater than zero but sufficiently low as to
not further traumatize artery M1720. Alternately, the release of
pressure can be maintained for a predetermined amount of time.
Alternately, the release of pressure can be maintained until
instructed by an operator who, for example, pushes a button to
close pressure release device M1745. After the release of pressure
terminates, the controller M1750 can instruct pump M1730 to turn
back on and re-pressurize the fluidic system. The pressure can
return to that pressure at which the compliance flow control system
M1735 activated the pressure release device M1745, or to another
pressure. The pump M1730, optionally, can be stopped at this
pressure, holding the pressure over some duration of time to allow
stress relaxation of the wall M1715 of artery M1720. Stress
relaxation can be allowed to proceed for a predetermined time, or a
predetermined decrease in pressure (which will occur during stress
relaxation) after which the pump M1730 resumes inflating the
inflatable device M1705.
[0548] Examples of fluid M250 include water, physiological saline
and other aqueous solutions, non-aqueous fluids, such as oils.
Examples of inflatable device M1705 include angioplasty balloons,
balloons for valvuloplasty, balloons for kyphoplasty, balloons for
enlarging portions of the gastro-intestinal system, or for
dilating, stretching, or distending any biological structure.
Examples of tube M1725 include needles, catheters, fused silica
tubing, glass tubing, or any narrow diameter rigid or flexible
fluidic conduit. Examples of pump M1730 include syringe or other
piston pumps, peristaltic pumps, or any pump sufficient to push
sufficient volume of fluid at sufficient pressure to inflate
inflatable device M1705 and, for some embodiments, to be
electrically actuated. The pressure release device M1745 can be a
valve that is normally closed and, on signal from the controller,
releases fluid from the fluidic system through a path of low fluid
resistance. Release of this fluid can be into a sterile container,
such as a plastic bag, to maintain sterility of the fluid inside
fluidic system M1700. Alternately, the pressure release device
M1745 can be the pump M1730 which, on signal from the controller
M1750, reverses the direction of pumping to decrease the fluid
pressure throughout the fluidic system M1700. Alternately pressure
release device M1745 can be a piston that, on actuation by
controller M1750, moves inside fluidic system M1700 such that
pressure decreases inside fluidic system M1700 sufficiently to
substantially reduce compliance flow.
[0549] Faster responses by compliance flow control system M1735 to
failure of the wall M1715 of artery M1720 or of wall M1710 of
inflatable device M1705 will reduce compliance flow into inflatable
device M1705 because faster responses result in more fluid being
directed by pressure release device M1745 out of fluidic system
M1700 before it can flow into tube M1725 and, thus, into inflatable
device M1705.
[0550] To further limit compliance flow arising from the tube
M1725, the wall M1755 of tube M1725 can have low compliance. For
example, the wall M1755 can be made of materials having low
compliance, such as glass, fused quartz, rigid polymers, or
ceramics. Alternately, the wall M1755 can be composed of materials
having higher compliance wrapped by fibers having lower
compliance.
[0551] To further limit compliance flow, the tube M1725 can possess
a high resistance to flow through the tube MI725. This high
resistance slows flow through the tube M1725 which thereby allows
more flow to be diverted out of the pressure release device M1745
before compliance flow control system M1735 responds. The
resistance to flow in tube M1725 can be achieved by using a small
internal diameter in tube M1725, such as 100 micrometers or
less.
[0552] FIG. 137 shows fluidic system M1800 which depicts an
alternate means by which resistance to flow in tube M1725 can be
achieved by using a small internal diameter over only the distal
region M1805 of tube M1725, such as a diameter less than 100
micrometers or less than 50 micrometers. The length of region M1805
also can be altered to control resistance in tube region M1805.
[0553] FIG. 138 shows an alternate fluidic system M1900 in which a
second pump M1905 is activated to decrease the pressure at the
proximal end M1726 of tube M1725. Second pump M1905 is placed in
fluid communication with the proximal end of tube M1725 such that
second pump M1905 serves as the pressure release device whereby the
controller M1750 signals second pump M1905 via signal M1746 to
reduce the pressure in fluidic system M1900. An alternative
embodiment would be to use a piston instead of pump M1905.
[0554] FIG. 139 shows an alternate embodiment of the fluidic system
in FIG. 136 that uses a pressure measuring device in the compliance
flow control system. In fluidic system M2000, the measuring device
of compliance flow control system M1735 is a first pressure
measuring device M2005 in fluid communication with the proximal end
M1726 of tube M1725. Controller M1750 is configured to receive a
signal M1741 from the first pressure measuring device M2005. The
controller M1750 performs a plurality of measurements based on the
pressure signal M1741 over time; for example, the controller can
sample the pressure signal for 1 second at 10 kHz. The controller
then compares a substantially instantaneous measurement of the
pressure signal, such as one or a few samples, to a variance in the
plurality of measurements over an interval of time preceding the
instantaneous measurement to detect rupture of the wall M1715 of
artery M1720 or of wall M1710 of inflatable device M1705 based on
that comparison. If rupture is detected, controller M1750 activates
pressure release device M1745 via activation signal M1746.
[0555] Fluidic system M2000 accomplishes many of the actions of
fluidic system M1000. Fluidic system M1000 places the first
pressure measuring device inside angioplasty balloon M1010.
However, pressure changes will transmit throughout any fluidic
system. The pressure changes will attenuate further from the source
of the change in pressure which is, in this case, sudden expansion
of the wall M1710 of inflatable device M1705 due to failure of wall
M1715 of artery M1720 or wall M1710 of inflatable device M1705. As
described for fluidic system MIOOO the devices and methods for
detecting tissue trauma by monitoring changes in force that are
disclosed in Section C-Detecting Tissue Trauma During Retraction
can be applied here.
[0556] FIGS. 130, 131, and 132 and their associated description,
therefore, can also be applied to fluidic system M2000. For
example, controller M1750 can determine the first time derivatives
of the pressure measurements, comparing a first time derivative
(such as the first time derivative approximated from two
consecutive samples or from a small number of samples) to the
average value of first time derivative over the preceding 0.1
seconds or 2 seconds, or over the preceding 1 second or 10 seconds.
A decrease in the first time derivative, as shown in FIG. 130,
would indicate failure of wall M1710 or wall M1715.
[0557] Similarly, the controller M1750 can determine the second
time derivatives of the pressure measurements, comparing a second
time derivative (such as the second time derivative approximated
from three consecutive samples or from a small number of samples)
to the average value of the second time derivative over the
preceding 0.1 seconds or 2 seconds, or over the preceding 1 second
or 10 seconds. A negative-going spike in the second time
derivative, as shown in FIG. 131, would indicate failure of wall
M1710 or wall M1715.
[0558] Similarly, the controller M1750 can estimate the variance in
the first or the second time derivatives of the pressure
measurements. The variance, calculated as the root mean square
(RMS) of the pressure signal, can pe determined from the most
recent pressure measurements and compared to the RMS from an
earlier time. An increase in variance in the first or second time
derivative, as shown in FIGS. 130 and 131, would indicate failure
of wall M1715 of artery M1720. Additionally, comparison of the
recent variance with the earlier variance can be determined as
their ratio, with an increase in the ratio of recent to earlier
variance being compared to a threshold value. A ratio that
substantially exceeds the threshold value would then indicate
failure of wall M1710 or wall M1715.
[0559] FIG. 140 illustrates an alternate fluidic system M2100 in
which flow measuring devices are used to detect failure of a
biological tissue, such as wall M1715 of artery M1720. A mass flow
sensor is an example of a flow measuring device. A first flow
measuring device M2105 is located at the outlet of the pump M1730,
and a second flow measuring device M2110 is located at the distal
end M1727 of the tube M1725 in fluid communication with the
inflatable device M1705. The controller M1750 configured to receive
first flow signal M2116 from first flow measuring device M2105 and
second flow signal M2117 from second flow measuring device M2110.
Controller also is configured to compare these two flow signals.
Compliance flow control system M2105 is thus comprised of
controller M1750, first flow measuring device M2105 sending first
flow signal M2116 to controller M1750, second flow measuring device
M2110 sending second flow signal M2217 to controller M1750,
pressure release device M1745 receiving activate signal M1746 from
controller M1750, and, optionally, pump signal M1731 to pump M1730
from controller M1750. A failure of wall M1715 of artery M1720
would result in a sudden expansion of inflatable device M1705
driven by compliance flow. Flow measured at second flow measuring
device M2110 would, therefore, become larger than flow measured at
first flow measuring device M2105 because flow at first flow
measuring device M2105 equals the flow of the pump M1730 and flow
at second flow measuring device M2110 equals the flow of pump M1730
plus the compliance flow driven by compliance in the fluidic system
M2100 downstream of pump M1730. Controller M1750 would detect this
change in flow and trigger the pressure release device M1745 to
minimize compliance flow into the inflatable device M1705, thereby
reducing trauma to artery M1720.
[0560] FIG. 141 illustrates another fluidic system M2200 in which a
single flow measuring device M2205 measures the flow at the
proximal end M1726 of tube M1725. Instead of using two flow
measuring devices as in fluidic system M2100, here in fluidic
system M2200 the flow rate of the pump M1730 is set by the
controller M1750 and is thus known. The flow measured at flow
measuring device M2205 is compared by controller M1750 to the set
flow rate. A failure of the wall M1715 of artery M1720 would result
in a sudden expansion of inflatable device M1705 driven by
compliance flow. Flow measured at the flow measuring device M2205
would, therefore, become larger than the set flow, which would be
conveyed by flow signal M2206 to controller M1750. Controller M1750
would detect this increase and trigger the pressure release device
M1745 via activate signal M1746 to minimize compliance flow into
inflatable device M1705, thereby reducing trauma to artery M1720.
Optionally, a compliant fluidic component M2210 can be placed
between flow measuring device M2205 and pump M1730 to act as a
fluidic "capacitator" to damp oscillations in the flow induced by
pump M1730 that would, otherwise, appear as noise in flow signal
M2206.
[0561] FIG. 142 shows a fluidic system M2300 that is similar to
fluidic system M2100; however, in fluidic system M2300 second flow
measuring device M2110 measures flow at the proximal end M1726 of
tube. The two flow signals, M2116 and M2117 are compared by
controller M1750 with flow measured by second flow measuring device
M2110 being greater than flow measured by first flow measuring
device M2105 as the indicator that there has been a failure of the
wall M1715 of artery M1720.
[0562] FIG. 143 shows a fluidic system M2400 that uses two pressure
measuring devices instead of flow measuring devices to detect and
reduce trauma to biological tissue. Fluidic system M2400 has a
compliance flow control system M2405 comprised of a controller
M1750 configured to first pressure signal M2411 from first pressure
measuring device M2410 that measures fluid pressure at the proximal
end of tube M1725, to second flow signal M2416 from second pressure
measuring device M2415 that measures fluid pressure at the distal
end M1727 of tube M1725, and to activate signal M1746 to pressure
release device M1745. The tube M1725 has sufficient resistance to
fluid flow that if the wall M1715 of artery M1720 fails, resulting
in a rapid release of pressure inside inflatable device M1705, then
the compliance flow does not immediately balance the pressures
between first pressure measuring device M2410 and a second pressure
measuring device M2415. Controller M1750, therefore, detects a
lower pressure at second pressure measuring device M2415 and
activates pressure release device M1745 to reduce compliance
flow.
[0563] As stated above, changes in pressure at one point in the
system can be detected throughout the system. The change in
pressure at a more distant point will lag any changes that occur in
a point closer to the initial change in pressure, and the magnitude
of the pressure change will probably be attenuated. Nevertheless,
changes in pressure elsewhere in a fluidic system can be used to
detect failure in the biological tissue.
[0564] FIG. 144 illustrates fluidic system M2500 that is similar to
fluidic system M2400 except that second pressure measuring device
M2415 is now located at the outlet of pump M1730. Pressure changes
arising from failure of the wall M1715 of artery M1720 will be
sensed at both the first pressure measuring device M2410 and the
second pressure measuring device M2415. A fluid path M2510 having
sufficiently high resistance to flow to create a pressure
difference of sufficient magnitude between the two pressure
measuring devices is located between the two pressure measuring
devices. Thus, if there is a drop in pressure inside inflatable
device M1705, then the pressure will drop first at first pressure
measuring device M2410 and then at second pressure measuring device
M2415. Controller M1750, therefore, can detect failure of the wall
M1715 of artery M1720 by comparing the two measured pressures and
then activate pressure release device M1745 to reduce compliance
flow.
[0565] FIG. 145 illustrates fluidic system M2600 that is similar to
fluidic system M2500 but that permits alternate placement of second
pressure measuring device M2415 to facilitate assembly of the
system. Second pressure measuring device M2415 measures the fluid
pressure inside a blind-ended fluid reservoir M2610 separated from
the rest of the fluidic system by a fluid path M2615 having high
fluid resistance to flow. If there is a drop in pressure inside
inflatable device M1705, then the pressure will drop first at first
pressure measuring device M2410 and then at second pressure
measuring device M2415. Controller M1750, therefore, can detect
failure of the wall M1715 of artery M1720 by comparing the two
measured pressures and then activate pressure release device M1745
to reduce compliance flow. An advantage of this assembly is that
the relative timing of the changes in the measured pressures can be
altered by connecting the fluid path M2615 to different points of
fluidic system M2600. The relative timing and magnitudes are set by
the distances separating the inflatable device M1705 and the
pressure measuring devices M2415 and M2410 and by the resistance to
flow of all connecting fluid channels, tubes, and other
conduits.
[0566] This latter statement is generally true for any of the
fluidic systems presented here--the relative timing of and
magnitudes of pressure changes are set by the distances separating
the inflatable device M1705 and the pressure measuring devices and
by the resistance to flow of all connecting fluid channels.
Compliant components can also be added to act as fluidic
"capacitors" that act as low-pass filters of pressure changes
through a point in the fluidic system. Larger volume and higher
compliance lowers the cut-off frequency of the compliant component.
Additionally, the flow rate from the pump is at all times knowable,
being determined by the controller. Therefore, the controller,
having set the flow rate, can calculate the expected pressures
throughout the system and then use deviations of measured pressures
from calculated pressures to indicate failure of the biological
tissue. Consider fluidic system M2400, the controller M1750 can
calculate the expected pressure at distal end M1727 of tube M1725.
If the measured pressure is less than the calculated pressure, then
this would indicate a failure of the wall M1715 of artery M1720.
Similarly, consider fluidic system M2500, the controller M1750 can
calculate the expected pressure at the proximal end M1726 of the
tube M1725. If the pressure measured by first pressure measuring
device M2410 is less than the calculated pressure, then this would
indicate a failure of the wall M1715 of artery M1720. Any number of
configurations will work.
[0567] A difficulty with using pressure measuring devices, such as
described in FIGS. 139, 143, 144, and 145 is that detecting failure
of the biological tissue can require detection of small pressure
changes over a broad range of pressures. High sensitivity over a
broad dynamic range is challenging because noise in the signal can
mask smaller changes in pressure, making it difficult to detect
smaller changes in pressure.
[0568] This difficulty can be alleviated by using differential
pressure measuring devices configured in a manner known in the
prior art and as shown in FIG. 146. A differential pressure
measuring device M2705 measures the pressure at a first point M2710
in fluid M250 relative to the pressure at a second point M2715 in
fluid M250. Both points can experience a broad range of pressure
within fluid M205, but the pressure difference between the two
points M2710 and M2715 can be limited to pressures well within the
pressure measuring range of the differential pressure measuring
device M2705. In fact, if points M2710 and M2715 are separated by a
fluid channel M2720 having a constant and known resistance to fluid
flow, the measured differential pressure will be proportional to
the flow rate through the fluidic channel M2720, making this
combination of differential pressure measuring device M2705 and
fluid channel M2720 with known resistance a flow measuring device
M2725 that reports the differential pressure/flow rate as a single
signal M2730. Fluid channels M2720 having higher resistance to flow
will result in higher pressure differentials for a given rate of
flow (or lower flows for a given pressure differential). Flow
measuring device M2725 can thus be used as the flow measuring
device in fluidic systems M2100, M2200, and M2300.
[0569] FIG. 147 illustrates fluidic system M2800 that is like
fluidic system M2300, but now flow measuring device M2725 is used
in place of flow measuring device M2205. Optionally, a compliant
fluidic component M2210 can be placed between pump M1730 and flow
measuring device M2725 to damp out pressure variations from the
pump that would otherwise appear as noise in the signal M2730 from
flow measuring device M2725. First pressure measuring point M2710
is located nearer the pump M1730 and second pressure measuring
point M2715 is located further from the pump M1730. A fluid path
M2715 of know resistance connects first pressure measuring point
M2710 to second pressure measuring point M2720. Controller M1750
receives flow signal M2730. Controller M1750 sets the rate of
pumping of the pump M1730, so the flow rate in fluidic system M2800
is known. The controller thus uses the condition that the measured
flow rate is higher than the set flow rate as the indicator that
there is a rupture of either the biological tissue (e.g. the wall
M1715 of artery M1720) or the wall M1710 of inflatable device
M1705.
[0570] Alternatively, if fluid path M2720 in fluidic system M2800
is of unknown resistance to flow, time variance in the signal M2730
from differential pressure measuring device M2705 can also be used
to detect failure of the wall M1715 of artery M1720 or the wall
M1710 of inflatable device M1705. FIGS. 130, 131, and 132 and their
associated description can be applied to fluidic system M2800. For
example, the controller M1750 can determine the first time
derivatives of the differential pressure measurements, comparing a
first time derivative (such as the first time derivative
approximated from two consecutive samples or from a small number of
samples) to the average value of the first time derivative over the
preceding 0.1 seconds or 2 seconds, or over the preceding 1 second
or 10 seconds. A decrease in the first time derivative, as shown in
FIG. 130, would indicate failure of wall M1715 of artery M1720.
[0571] Similarly, the controller M1750 can determine the second
time derivatives of the pressure measurements, comparing a second
time derivative (such as the second time derivative approximated
from three consecutive samples or from a small number of samples)
to the average value of second time derivative over the preceding
0.1 seconds or 2 seconds, or over the preceding 1 second or 10
seconds. A negative-going spike in the second time derivative, as
shown in FIG. 131, would indicate failure of wall M1715 of artery
M1720.
[0572] Similarly, the controller M1750 can estimate the variance in
the first or the second time derivatives of the pressure
measurements. The variance, calculated as the root mean square
(RMS) of the pressure signal, can be determined from the most
recent pressure measurements and compared to the RMS from an
earlier time. An increase in variance in the first or second time
derivative, as shown in FIGS. 130 and 131, would indicate failure
of wall M1715 of artery M1720. Additionally, comparison of the
recent variance with the earlier variance can be determined as
their ratio, with an increase in the ratio of recent to earlier
variance being compared to a threshold value. A ratio that
substantially exceeds the threshold value would then indicate
failure of wall M1715 of artery M1720.
[0573] FIG. 148 illustrates a fluidic system M2900 capable of rapid
responses. It has a compliance flow control system M2905 using a
first differential pressure measuring device M2910 generating a
first flow signal M2915 from flow (between first pressure measuring
point M2912 and second pressure measuring point M2913) and a second
differential pressure measuring device M2920 generating a second
flow signal M2925 from flow (between third pressure measuring point
M2922 and fourth pressure measuring point M2923). The first flow
channel M2911 separating the two pressure measuring points of
differential pressure measuring device M2910 and the second flow
channel M2921 for second pressure measuring device M2920 may be
known or not. Comparator M2930 compares the two flow signals to
produce a differential flow signal M2935. Differential flow signal
M2935 is then used by controller M1750 as the indictor of failure
of wall M1715 of artery M1720 or of the wall M1710 of inflatable
device M1705. Pump M1730 pressurizes the fluid M250 inside fluidic
system M2900, driving fluid M250 to inflate inflatable device
M1705. First compliant fluidic component M2210 can, optionally, be
used to remove fluidic flow noise from pump M1730. Fluid M250 flows
through conduits M5 from pump M1730 through first compliant fluidic
component M2210 to first differential pressure measuring device
M2910, then to pressure release device M1745, then to second
differential pressure measuring device M2920, and then through tube
M1725 to inflatable device M1705. If the wall M1715 of artery M1720
should rupture, then the resulting compliant flow into inflatable
device M1705 will increase the pressure differential across the two
pressure measuring points M2922 and M2923 of second differential
pressure measuring device M920. Additionally, as long as the
resistance to fluid flow inside fluid channels M2911 and M2921 is
not too great when pump MI730 is pumping, then higher resistances
will slow compliance flow into tube M1725 from upstream (closer to
the pump M1730), effectively giving compliance flow control system
M2905 more time to respond. Second compliant fluidic component
M2940 can, optionally, be used to sustain pressure upstream,
keeping small the differential pressure at first differential
pressure measuring device M2910. If wall M1715 of artery M1720
should fail, the resulting compliance flow into inflatable device
M1705 will cause a drop in pressure at fourth pressure measurement
point M2923, producing a larger pressure differential at second
differential pressure measuring device M2920. Meanwhile, the
resistance to flow inside fluid channel M2911 and the
pressure-volume reservoir inside second compliant fluidic component
M2940 will sustain the pressure at second pressure measuring point
M2913, so the pressure differential will remain little changed at
first differential pressure measuring device M2910. Thus, the first
flow signal M2915 will change less, and second flow signal M2925
will change more. Comparator M2930 will then change differential
flow signal M2935, which is detected by controller M1750 which then
activates pressure release device M1745 via signal M1746 which
directs compliance flow out of fluidic system M2900 and away from
the proximal end M1726 of tube M1725, reducing compliance flow into
tube M1725 and thus into inflatable device M1705.
[0574] Compliance flow control system M2905 can detect rupture of
the wall M1710 of inflatable device M1705 or of wall M1715 of
artery M1720 by sensing the increase in the pressure differential
at second pressure measuring device M2920 relative to first
pressure measuring device M2910. This can be accomplished by a
ratiometric method such that differential flow signal M2935 from
comparator M2930 changes with the ratio of signal M2915 to signal
M2925. Thus, comparator M2930 can be a very fast device, including
digital electronic devices and analog electronic devices, such as
an operational amplifier, to shorten the response time of
compliance flow control system M2905. Furthermore, differential
flow signal M2935 can be compared to a threshold value, and if the
differential flow signal M2935 differs from that threshold value,
then controller M1750 can activate pressure release device M1745.
Alternatively, the differential flow signal M2935 can be compared
to earlier values of the differential flow signal M2935, and a
change beyond a threshold can be used by the controller M1750 to
activate the pressure release device M1745.
[0575] Alternatively, time variance in the signal M2935 from
comparator M2930 can also be used to detect failure of the wall
M1715 of artery M1720 or the wall M1710 of inflatable device M1705.
FIGS. 130, 131, and 132 and their associated description can be
applied to fluidic system M2900. For example, the controller M1750
can determine the first time derivatives of the signal M2935,
comparing a first time derivative (such as the first time
derivative approximated from two consecutive samples or from a
small number of samples) to the average value of the first time
derivative over the preceding 0.1 seconds or 2 seconds, or over the
preceding 1 second or 10 seconds. A decrease in the first time
derivative, as shown in FIG. 130, would indicate failure of wall
M1715 of artery M1720.
[0576] Similarly, the controller M1750 can determine the second
time derivatives of signal M2935, comparing a second time
derivative (such as the second time derivative approximated from
three consecutive samples or from a small number of samples) to the
average value of second time derivative over the preceding 0.1
seconds or 2 seconds, or over the preceding 1 second or 10 seconds.
A negative-going spike in the second time derivative, as shown in
FIG. 131, would indicate failure of wall M1715 of artery M1720.
[0577] Similarly, the controller M1750 can estimate the variance in
the first or the second time derivatives of signal M2935. The
variance, calculated as the root mean square (RMS) of the signal
M2935, can be determined from the most recent values of signal
M2935 and compared to the RMS from an earlier time. An increase in
variance in the first or second time derivative, as shown in FIGS.
130 and 131, would indicate failure of wall M1715 of artery M1720.
Additionally, comparison of the recent variance with the earlier
variance can be determined as their ratio, with an increase in the
ratio of recent to earlier variance being compared to a threshold
value. A ratio that substantially exceeds the threshold value would
then indicate failure of wall M1715 of artery M1720.
[0578] All of fluidic systems M1700 through M2900 could be
configured as larger, self-contained rack-mount systems used in a
hospital operating room. As such, they could be configured with all
pumps, control circuitry, and other components in a single package.
These fluidic systems could also be configured as much smaller,
hand-held units that attach to many of the catheters and pumps
currently on the market. They could be made as reusable units or
even as single-use units to facilitate sterile use.
[0579] The embodiments set forth herein are examples and are not
intended to encompass the entirety of the invention. Many
modifications and embodiments of the inventions set forth herein
will come to mind to one skilled in the art to which these
inventions pertain having the benefit of the teaching presented in
the foregoing descriptions and the associated drawings. Therefore,
it is to be understood that the inventions are not to be limited to
the specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are used herein, they are
used in a generic and descriptive sense only and not for the
purposes of limitation.
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