U.S. patent application number 09/816708 was filed with the patent office on 2001-10-25 for pressure sensor for therapeutic delivery device and method.
Invention is credited to Tom, Curtis P..
Application Number | 20010034501 09/816708 |
Document ID | / |
Family ID | 22706163 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010034501 |
Kind Code |
A1 |
Tom, Curtis P. |
October 25, 2001 |
Pressure sensor for therapeutic delivery device and method
Abstract
The present invention is an apparatus for treating a selected
patient tissue or organ region, at the surface of such region. The
apparatus has an accessing tool for accessing the patient region,
the tool having a distal end, and a proximal end at which the tool
can be manipulated to place the distal end adjacent to the patient
region. The apparatus also has a probe carried on the distal end
and defining a contact surface that may be urged against the
patient region thereby creating contact pressure. A pressure
transducer is operatively coupled to the probe and is capable of
producing a measurable response to the contact pressure. A
monitoring device is operatively connected to the pressure
transducer, for determining the contact pressure. An effector is
operatively disposed on the probe for producing a given effect on
the patient region when the effector is activated, and an activator
operatively connected to the effector, by which the effector can be
activated.
Inventors: |
Tom, Curtis P.; (Menlo Park,
CA) |
Correspondence
Address: |
IOTA PI LAW GROUP
350 CAMBRIDGE AVENUE SUITE 250
P O BOX 60850
PALO ALTO
CA
94306-0850
US
|
Family ID: |
22706163 |
Appl. No.: |
09/816708 |
Filed: |
March 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60191610 |
Mar 23, 2000 |
|
|
|
Current U.S.
Class: |
604/67 ;
600/466 |
Current CPC
Class: |
A61B 5/6852 20130101;
A61B 2017/22077 20130101; A61B 2090/062 20160201; A61B 2018/00392
20130101; A61B 2090/064 20160201; A61B 17/3478 20130101; A61B
2017/348 20130101; A61B 5/6885 20130101; A61M 5/32 20130101; A61B
2017/00247 20130101; A61B 17/3494 20130101; A61B 17/3207
20130101 |
Class at
Publication: |
604/67 ;
600/466 |
International
Class: |
A61M 031/00; A61B
008/14 |
Claims
what is claimed:
1. Apparatus for treating a selected patient tissue or organ
region, at the surface of such region, comprising an accessing tool
for accessing the patient region, said tool having a distal end and
a proximal end at which the tool can be manipulated to place the
distal end adjacent such patient region, a probe carried on said
distal end and defining a contact surface that may be urged against
said patient region thereby creating contact pressure, a pressure
transducer operatively coupled to said probe and capable of
producing a measurable response to the contact pressure, a
monitoring device operatively connected to said pressure
transducer, for determining the contact pressure, an effector
operatively disposed on said probe for producing a given effect on
the patient region when effector is activated, an activator
operatively connected to said effector, by which said effector can
be activated.
2. The apparatus of claim 1, wherein said monitor is operatively
connected to a user readable display.
3. The apparatus of claim 1, wherein said activator is operatively
connected to said monitor and activates said effector at a
pre-selected range.
4. The apparatus of claim 1, wherein said monitoring device is
operable to measure the range over which the pressure transducer is
responsive to changes in the force applied to the transducer, and
to determine from such range, a contact-pressure range within which
activation of the effector is optimized for treatment effect.
5. The apparatus of claim 1, wherein said pressure transducer is
responsive to the magnitude and direction of force applied to the
transducer, and said monitor is operable to determine both the
contact pressure and the approximate incidence angle of said tool
with respect to the surface of the patient region.
6. The apparatus of claim 5, wherein said pressure transducer
includes a plurality of pressure-transducer units, each carried on
the probe's contact surface, and said monitoring device is operable
to determine from the force applied to each unit, the orientation
of the said tool with respect to the surface of patient tissue with
which said is in contact.
7. The apparatus of claim 5, wherein said pressure transducer
defines an axis of least strain along which force can be applied to
the tool's head, and the transducer is responsive to force
components applied along the axis and off axis.
8. The apparatus of claim 5, wherein said probe is movably mounted
on the distal end of said tool, and the pressure transducer
includes position-sensing means for sensing the position of the
probe with respect to the distal end of the tool.
9. The apparatus of claim 1, wherein said pressure transducer
includes (i) first and second conductors, (ii) an insulating layer
adjacent the first conductor, said layer having perforations
therein, and (iii) a conductive elastomer disposed between the
insulating layer and the second conductor and in constant contact
with the second conductor; wherein, during operation of the
transducer, an electrical excitation signal applied to the two
conductors and the impedance therebetween varies with a force
applied to the contact surface of the transducer to generate an
information signal indicative of whether or not the force applied
to the contact surface is above a predetermined threshold, and, if
so, the magnitude of the applied force.
10. The apparatus of claim 9, wherein said conductive elastomer
temporarily flows through the perforations in the non-conductive
layer and makes contact with the first conductor, when the applied
force is above the predetermined threshold.
11. The apparatus of claim 1, wherein said monitoring device is
operably connected to said activator, to activate said effector
when such contact pressure is within a selected pressure range.
12. The apparatus of claim 1, for use in promoting angiogenesis in
an under-oxygenated region of a patient's heart, wherein the
accessing tool is designed to access an exterior or interior
surface of such heart region from an external body site, and said
effector is designed to produce an angiogenic stimulus in the
myocardial layer of such region, upon activation of the
effector.
13. A pressure transducer comprising means defining a contact
surface, first and second conductors; an insulating layer having
perforations therein, the non-conductive material being adjacent to
the first conductor; and a conductive elastomer between the
insulating layer and the second conductor and in constant contact
with the second conductor; wherein, during operation of the
transducer, an electrical excitation signal applied to the two
conductors and the impedance therebetween varies with a force
applied to the contact surface of the transducer to generate an
information signal indicative of (i) whether or not the force
applied to the contact surface is above a predetermined threshold,
and, if so, (ii) the magnitude of the applied force.
14. The transducer of claim 13, wherein the information signal is
provided continuously and in real-time.
15. The transducer of claim 13, wherein the conductive elastomer
temporarily flows through the perforations in the non-conductive
layer and makes contact with the first conductor, when the applied
force is above the predetermined threshold.
16. The transducer of claim 15, wherein the electrical excitation
signal remains substantially unchanged when the applied force is
below the predetermined threshold.
Description
[0001] This application claims priority of U.S. Provisional Patent
Application No. 60/191,610 filed Mar. 23, 2000, which is
incorporated in its entirety herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an apparatus and method for
affecting a body tissue, such as the heart, at the tissue surface,
for purposes of injecting material into the tissue or otherwise
stimulating a desired therapeutic effect on the tissue.
BACKGROUND OF THE INVENTION
[0003] Percutaneous catheter-based treatments of cardiovascular
disease require that navigation of the catheter within the body be
done with a mode of visualizing the catheter as it is moved within
the body. The most popular mode of visualization is X-ray
fluoroscopy, where an operator is able to monitor a radiopaque
device as it travels within a body lumen, such as the
cardiovascular system.
[0004] Recently, interventional procedures that require catheter
navigation within the chambers of the heart have been developed;
these include electrophysiological mapping and ablation and
transmyocardial revascularization. These procedures also often
require that the tip of the catheter be placed in contact with a
wall of the beating heart in order to deliver the desired treatment
safely. Potential complications of this procedure may be
perforation of the wall when excessive force is applied or
ineffective treatment due to poor tip contact. Under fluoroscopic
guidance it is often difficult to assess when the catheter tip has
reached the wall because live fluoroscopy does not visualize that
wall itself, since it is not radiopaque. For the same reason, even
after the catheter tip has reached the wall, it is difficult to
determine whether the tip consistently remains in contact with the
wall or if excessive force is applied to the wall. Finally, it is
also difficult to determine whether the catheter tip is
substantially perpendicular to the wall because fluoroscopy yields
a two-dimensional image of the device in three-dimensional
space.
[0005] Thus, for procedures where a medical instrument must be
placed in firm but not excessive contact with anatomical surface,
there is an apparent need for a device which is able to provide
information to the user of the instrument that is indicative of the
existence and magnitude of the contact force. Furthermore, for
procedures where the medical instrument must also be placed either
perpendicular or at some selected angle to the anatomical surface,
there is an apparent need for a device which is able to provide
information to the user of the instrument that is indicative of the
incident angle of the contact force with respect to the anatomical
surface.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of this invention to provide such
a device for overcoming the above-mentioned problems.
[0007] It is another object of this invention to provide
information to the user of a medical instrument, such as a
catheter, that must be placed in contact with the surface of an
anatomical structure, to increase the likelihood of safely
delivering the desired treatment while reducing the possibility of
inflicting perforation type injuries or providing inadequate
treatment.
[0008] It is further an object of this invention to provide a
method for generating information regarding whether the tip of a
medical instrument, such as a catheter or probe, is in contact with
a surface of a tissue or organ, and, if so, the magnitude of the
contact force and the incident angle of the contact force with
respect to the anatomical surface.
[0009] In summary, the present invention is an apparatus for
treating a selected patient tissue or organ region, at the surface
of such region. The apparatus has an accessing tool for accessing
the patient region, the tool having a distal end, and a proximal
end at which the tool can be manipulated to place the distal end
adjacent to the patient region.
[0010] The apparatus also has a probe carried on the distal end and
defining a contact surface that may be urged against the patient
region thereby creating contact pressure. At least one pressure
transducer, wherein each pressure transducer is operatively coupled
to the probe and is capable of producing a measurable response to
the contact pressure experienced adjacent to the pressure
transducer. A monitoring device is operatively connected to each
pressure transducer, for determining contact pressure. At least one
effector, wherein each effector is operatively disposed on the
probe for producing a given effect on the patient region when the
effector is activated, and an activator operatively connected to
the effector, by which the effector can be activated.
BRIEF DESCRIPTION OF THE FIGURES
[0011] FIG. 1 illustrates the force contact transducer attached to
a probing tool and monitoring circuitry;
[0012] FIG. 2 is an exploded view of a force contact transducer
constructed in accordance with embodiments of the invention;
[0013] FIG. 3 illustrates a view of the cap and base of the force
contact transducer;
[0014] FIG. 4 illustrates a view of the cap region of the force
contact transducer;
[0015] FIG. 5 illustrates a detailed exploded view of contact
elements of the invention;
[0016] FIG. 6 illustrates one embodiment of the invention that
employs a thin film transducer array disposed around a tool
shaft;
[0017] FIGS. 7A-7D illustrate embodiments of a transducer array and
a single transducer;
[0018] FIG. 8 illustrates, in simplified view, the cap region of a
transducer capable of detecting both axial and lateral force
components applied to the sensor; and
[0019] FIG. 9 illustrates an embodiment of the invention of the
invention that measures force movement by electrical inductance,
rather than by resistance.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 1 shows an apparatus 44 constructed according to the
invention. The apparatus provides an assembly or tool 46, for
accessing a patient tissue or organ region 47, and a sensor device
20, detailed below, for determining the pressure of the probe
against the target tissue and, in some embodiments, the angle of
contact between the probe and target tissue.
[0021] In general application, the assembly is used to access an
internal target region, and to provide a therapeutic stimulus, such
as injection of a therapeutic compound or gene, forming a laser
channel, or introducing an injury, e.g., by ultrasonic waves,
infrared radiation, or mechanical injury on below the surface of
the target region. E.g., to stimulate an angiogenic response in the
target region. The therapeutic stimulus is preferably
administered/provided through the assembly probe. The sensor device
operates, in accordance with the invention, to provide information
to the user about the position of the probe with respect to the
target region, since the target region is generally not directly
viewable by the user, e.g., physician.
[0022] In the embodiment shown, the medical instrument includes a
rigid shaft 46, which may have a curved section, as shown in FIG.
1. Alternatively, the medical instrument is a flexible catheter,
e.g., for delivery of a therapeutic stimulus to a target site
within the vasculature or heart. The distal end of the shaft may be
the base of the transducer, as shown in FIG. 1, or a separate
element securely affixed to base. A handle 48 is attached to the
proximal end of the shaft or base. In one embodiment, the shaft is
pivotally attached to the transducer base to permit the tip of the
medical instrument to bend. The handle includes a control panel 50
having for control of the instrument by the user. Also shown are a
bridge divider, an output device 54, such as a display device, and
signal processing circuitry 56 whose operation is described
below.
[0023] While not detailed here, handle 48 is designed to produce a
selected therapeutic effect on target tissue, when a desired
pressure and/or pressure contact angle is sensed between the probe
and target tissue. The therapeutic effect may be the injection, by
a needle or needleless injection system, of a solution or
suspension of a therapeutic compound or gene, or a radiation or
ultrasound injury produced by an light-carrying fiber or sonic
device on the probe, or a mechanical injury produced by a
mechanical tool on the probe, as in conventional. The apparatus is
therefore equipped, according to well-known devices, to provide an
extendable needle, a light fiber, an extendable mechanical-injury
device, or the like to produce the desired therapeutic effect, in
response to a signal applied by the user to handle 48. That is,
handle 48 includes structure for activating the therapeutic
receptor at the distal end of the apparatus. In one embodiment, the
therapeutic response is activated when the distal end of the
apparatus is positioned against the target tissue with a desired
pressure, that is, above a selected pressure threshold or within a
desired pressure range, as determined from the pressure sensor
device of the invention. In addition, angle of contact as sensed by
the device may be employed as a variable to be considered in an
automated triggering.
[0024] FIG. 2 is an exploded view of a force contact transducer or
device 20 constructed in accordance with embodiments of the
invention. Device 20 includes an elongate, cylindrical base 22 that
may be constructed of non-conductive material such as polycarbonate
or a metallic conductive material such as surgical steel or similar
material. The base has a larger diameter portion 24 that may serve
as, or be attached to, a shaft of an associated medical instrument,
such as needle-delivery device or light fiber, in which the
transducer is incorporated. Extending from the distal end of the
larger diameter portion is a reduced diameter portion 26.
[0025] Attached to, or formed integrally with, the reduced diameter
portion is a flange 28 that has a central opening 28a and one or
more notches, such as notch 28c, formed in its outer edge. An upper
surface 28b of the flange is electrically conductive (by placement
of a not shown conductive layer and serves as one of the electrical
conductors of the transducer. The details of the base are
illustrated in FIG. 4.
[0026] Device 20 further includes a cap 30, which is generally
cylindrical in shape and has an axial bore extending therethrough
to define an inner wall. A plurality of rectangular feet 30b are
formed on one end surface 30c of the cap, which surface acts as the
second electrical conductor of the transducer. The cap is shown in
more detail in FIG. 4.
[0027] Sandwiched between conducting surfaces 30c and 28b are: (i)
a conductive or semi-conductive elastomer 32 that is preferably
made of carbon loaded silicone rubber or other material with
similar characteristics, and (ii) a thin, non-conducting insulating
layer 34 that is preferably made of mylar, polyimide or other
material which exhibits similar insulating or dielectric
properties. Each of these components 32 and 34 has an opening 32a
and 34a respectively formed therein so that these components may be
received on the reduced diameter portion 26 of base 22. A lower
surface 34b of the insulating layer abuts against, but does not
completely cover, conductor surface 28b, so that a lower surface
32b of the conductive elastomer is able to selectively make contact
with conductor surface 28b based on a force applied to the
transducer, as will be explained in more detail below.
[0028] In the illustrated embodiment, this is accomplished by
making opening 34b in the form of a slot, as seen best in FIG. 5.
However, this is merely one example; other arrangements are
possible. For example, the insulator may have a central opening a
plurality of radial arms providing a plurality of circumferential
slots through which electrical contact between in the elastomer and
the confronting conductive surface 28b of flange 28.
[0029] Formed along the outer edge of insulator 34 is a notch 34c,
which is aligned with notch 32c in elastomer 32 and slot 28c in
flange 28, as seen particularly in FIGS. 3 and 4. The notches
accommodate a pair of electrical leads 36a and 36b that are in
electrical contact with conducting surfaces 28b and 30c,
respectively, as shown in FIGS. 2 and 3.
[0030] Formed in an upper surface 32c of the conductive elastomer
is a plurality of indents or footprints that correspond to the feet
30b formed on conductive surface 30c of the cap. Each one of the
feet 30b is adapted to fit securely within its complementary
footprint to maintain constant contact between the conductive
surface of cap 30 and the upper surface of conductive elastomer
32.
[0031] It is desirable to seal the components of the contact force
transducer apparatus to prevent ingress of bodily or other fluids
into the electrical regions of the apparatus. Furthermore, it is
highly desired to seal the invention to prevent the egress of
components from the contact force transducer apparatus.
Accordingly, one skilled in the art would realize that numerous
means for sealing the apparatus are possible. For example, a
potting material may be introduced at component junctions so as to
seal the device without interfering with its intended function.
Alternatively and as discussed in detail below, a shroud or tip may
be employed to seal the apparatus. Such sealing means may be
preformed or formed in place, for example, by dipping an
appropriately masked apparatus in a sealing compound to create a
tip or shroud in place.
[0032] A tip element 38 may be employed to protect the cap. In one
embodiment, the tip has a lower end 38a that is securely attached
to an upper end of the cap, as shown in FIG. 2. In another
embodiment, the tip extends over the cap-conductive
elastomer-insulator assembly (not shown). In either case, when the
tip is used, its outer surface 38b acts as the contact surface of
the transducer. When the tip is not employed, the upper end of the
cap is the contact surface. The transducer components including the
tip in assembled form are shown in FIG. 2. When the tip is not
used, upper end 30d serves as the contact surface of the
transducer. The assembled transducer excluding the tip is shown in
FIG. 3.
[0033] If desired, a suitable biologically compatible coating or
cover 40 may be applied to the cap-conductive
elastomer-insulator-flange assembly (and tip if included) to
protect it and to prevent fluid ingress. Such a cover or coating,
with portions broken away, is shown in FIG. 2.
[0034] A second embodiment of the invention (not shown) is similar
to the first except that it further includes a thin insulator which
fits between cap 30 and tip 38 to reduce the friction between these
components and enable them to move relative to each other as the
force applied to the contact surface of the transducer is
varied.
[0035] In operation, an electrical excitation signal is generated
in a bridge or divider circuit 52 (FIG. 1) and applied to the
conductive surfaces or other electrical elements of the sensor
described below. If a force below a predetermined threshold is
applied to the contact surface of the transducer, the excitation
signal will remain the same. However, if the applied force is just
above the predetermined threshold, conductive elastomer 32, which
is in constant contact with conductive surface 30c, will extend or
be pushed through the openings or perforations in insulating layer
34 to make contact with conductive surface 28b. This causes the
impedance between the two conductive surfaces to decrease,
producing a change in the excitation signal which indicates that
minimum contact has been made. As the applied force is further
increased, the conductive elastomer compresses causing a further
proportional drop in the impedance that, in turn, produces
corresponding change in the excitation signal. Thus, the impedance
and therefore the excitation signal varies with the magnitude of
the applied force.
[0036] The bridge/divider circuit is in electrical communication
with an output device 54 which may be in the form of audio or
visual device adapted to provide an information signal to the user
indicative of whether the outer surface of the transducer has made
contact, and, if so, the magnitude of the contact. The output
device may take a variety of different forms. For example, an LED
bar graph or other display capable of rendering a graphical or
visual representation may be used to provide a continuous,
quasi-continuous or discrete indication of the magnitude of a force
applied to the contact surface of the transducer, from a minimum
applied force indicative of minimum contact to a predetermined
maximum. Alternatively, or in addition to, a speaker or other audio
device may be used to emit a sound when minimum contact is made and
emit proportionally louder sounds as the firmness of the contact
increases.
[0037] The sensitivity of the excitation signal and hence the
information signal may be adjusted in a number of different ways.
One way is by using an elastomer with a different conductivity
and/or compressibility. Another way is with electronic signal
processing circuitry with adjustable amplification and filtering.
Such a signal processing circuit (56) may be physically integrated
with the bridge/divider circuit, or may be a separate circuit that
is in electrical communication with the bridge/divider circuit, as
illustrated in FIG. 1. The sensitivity of the signals (excitation
and information) may also be adjusted by varying the size of the
openings or perforations in the insulating layer, or by varying the
thickness of the insulating layer. Larger perforations increase the
sensitivity. In any case, the sensitivity of the transducer is set
based on the desired contact force threshold and the minimum
magnitude of change to be detected.
[0038] A flat transducer contact surface will generate less of an
output signal if the tip is in contact with tissue surface at an
oblique angle. On the other hand, a rounded or tapered contact
surface will generate a greater output signal at an oblique angle
of contact. Thus, the geometry of the contact surface may be
tailored to provide feedback about the perpendicularity of the
contact between the medical instrument tip and the tissue surface.
Optionally, the friction coefficient of the tip or exposed cap
material at the contact surface may be altered to provide for shear
force as the probe is situated upon a tissue surface in a way that
a lateral force vector component manifests, assuming at least some
of the thrust force applies creates a later force component. The
less the friction between the contact surface and the tissue
surface, the less the shear or lateral force component
realized.
[0039] In another embodiment, a plurality of discrete transducers
can be distributed on the tip of a medical instrument to provide
further information regarding the perpendicularity of the contact.
In the case of two transducers, each covers 180 degrees of the tip
surface; in the case of three transducers, each covers 120 degrees,
etc. The combined signal from the multiple transducers may be
processed to provide, in addition to contact and magnitude
information, angle of contact of information as well.
[0040] In another particularly preferred embodiment, a transducer,
or transducers if contact angle sensing is sought, may comprise a
thin double mylar film layered sandwich as described in Krivopal,
U.S. Pat. No. 5,989700, herein incorporated in its entirety by
reference. Looking at FIG. 6, the instant invention differs from
Krivopal in that sensor 60 has sensor elements 68 on a support 70
having an aperture 76 disposed in the center to permit tool shaft
64 to be disposed at a normal angle through the sensor or sensor
array. Each individual sensor area is electrically accessible by
leads 66.
[0041] The sensor support 70 which can either be rigid, or elastic
depending on the degree of flexibility sought in the device.
Disposed above the sensor support is a resilient or elastomeric cap
72 which mechanically communicates the probe tip contact surface
incident angle and total contact force downward to sensor 60. Cap
72 may further include protuberances 78 to focus the communicated
force onto sensors 68.
[0042] The entire probe tip may be covered by a sheath, not shown.
Alternatively, a transducer, such as a thin film transducer, may be
positioned directly on the contact surface, thereby creating a
superior contact surface. Alternatively, the probe may lack a cap
element and thus directly expose a transducer, such as a thin film
transducer, to a tip surface opposite the tip contact surface, or
the transducer may itself comprise the tip surface, and thus the
contact surface as well. Each of these embodiments just described
may include one or more transducers so that incident angle as well
as force may be detected.
[0043] Considering now the embodiments shown in FIGS. 7A-77D, a
sandwich 112 has a top mylar film 112a, an upper conductive ink
layer 112b applied to the lower surface region of the top mylar
film 112a, an upper semiconductive ink 112c applied to the upper
conductive ink layer 112b, an air gap 112d, a lower semiconductive
ink layer 112e disposed upon a lower conductive ink layer 112f
which is disposed on the upper surface of a bottom mylar film
112g.
[0044] There may be an insulting ring or sections surrounding the
above described ink sandwich to separate the upper mylar layer from
the lower mylar layer thus creating the air-gap between the upper
and lower semi-conductive ink layers. In the case of a multiple
transducer array 100, several sandwich regions 102, 104, 106 may be
arranged upon the plane created by the mylar film, each region
being in electrical communication with the monitoring unit, and
each region is independently responsive to the contact force
present at the corresponding region of the contact surface of the
probe thus providing a means of determining the incident angle of
the contact force with respect to the tissue surface by comparing
the individual responses of each transducer sandwich region.
[0045] Alternatively, each sandwich region 114 may be a separate
mylar film sandwich 116, with each electrode 118, 120 individually
in electrical communication with the monitor device.
[0046] In another embodiment, the pressure transducers may be a
combination to of a purely mechanical resilient device such as an
elastomeric spacer, and a mechanical or electrical device for
measuring the effect of the force upon the resilient device.
Measurement may include a mechanical deflection of mechanically
communicated information to a portion of the tool distal from the
patient surface, or may be a switch or potentiometer mechanically
operating is above its inherent mechanical (frictional) resistance.
Mechanically communicated deflection may be monitored and displayed
to a user as described below.
[0047] FIG. 8 shows another embodiment of a sensor device 80 for
use in the apparatus of the invention. The device shown here is
designed to measure both axial pressure, along an axis normal to
the contact face of the probe, and lateral direction, i.e., force
applied to a side region of the probe. The device includes a rigid
mechanical support 81 which is attached at its lower end in the
figure to the distal end of the accessing tool, and which provides
a central opening 82 through which the therapeutic effector, e.g.,
needle or optical fiber is received.
[0048] The device has a flexible cap 83 that is rigidly attached to
a radially extending annular ring 91 in the support. The cap is
formed of a flexible polymer or elastomer material or other
flexible material that permits the cap to deform when pressure is
applied to the cap, when the probe is in contact with the target
tissue. Carried on inner, upper surface of the cap is a preferably
segments annular electrode ring 84 positioned to contact an annular
conductive elastomer member 86 of the type described above, when an
axial pressure acts and distorts the upper surface of the cap. The
elastomer member, in turn, is seated on a insulative spacer 85 that
provides an electrical barrier between the elastomer and support,
but which provides openings or notches through which the elastomer
can be pressed, when an axial force acts on it, as described with
reference to FIGS. 1-4.
[0049] In operation, when an axial force is applied to the cap, the
cap is distorted to bring electrode ring 84 into contact with
elastomer member 86, pushing the elastomer through spaces in the
insulative spacer 85. This changes the resistance of a circuit
containing the two electrodes and the elastomer member in
proportion to the total contact area that the elastomer makes with
the support electrode, and this change in resistance is recorded
and displayed to the user.
[0050] Carried on the annular side region of the support is a
plurality of insulative members, such as elastomeric members 88a,
88b, arranged circumferentially about the support. Typically, the
device includes three such members, each member being carried on an
insulative spacer, such as spacers 89a, 89b. Similarly, carried on
the inner confronting surface of the cap is a segmented electrode
87 which is disposed to make contact with individual elastomer
members 84 when side regions of the cap are distorted by side
pressure and brought against the confronting elastomeric segments.
Thus, side-directed pressure is detected, as above, by a change in
the resistance in one or more or the side elastomer members, as the
cap electrodes push against the elastomer member(s), forcing
surface portions of the member(s) through openings in the spacers,
and lowering the resistance of each associated circuit containing
the affected elements. The user thus has information about axial
pressure, from the change in resistance (impedance) in the
upper-cap circuit, and information about angle of contact by the
extent of asymmetry in measured resistances of the three side
circuits.
[0051] In a purely mechanical device there may be disposed between
the probe and the proximal end of the tool an elastic resilient
support. Absent any surface contact, the probe's contact surface
remains perpendicular to the thrust axis of the tool because of the
elastic resilient support. Attached to the tool side of the probe
are the ends of at least 3 or more flexible shafts running parallel
or coherently through the tool length. These shafts run slidably
through and protrude beyond lumens within the tool body beginning
at the probe facing side of the proximal end of the tool and
terminating as openings at the distal or user end of the tool. As
the contact surface is deflected away from the thrust axis of the
tool, the distance between the probe contact surface and the tool
varies depending on the angle of deflection. The shaft, beneath
where the distance between the contact surface of the probe and the
proximal end of the tool is least, will protrude out more from the
distal or user end of the tool, whereas the shafts opposite will
recede into the tool at the distal or user end. Consequently, a
user will be able to observe angular relation of the probe to the
tool by observing the protrusion or withdrawal of the shafts,
thereby the user could adjust the incident angle of the tool to
achieve a balanced shaft display. One skilled in the art would
readily recognize that many variations of this embodiment are
possible, especially with respect to how the angular information is
displayed to the user.
[0052] In another multi-transducer embodiment, each pressure
transducer is independently elastically and resiliently related to
the contact surface, and another embodiment provides for each
pressure transducer being mutually elastically and resiliently
related to the contact surface.
[0053] In yet another embodiment, the monitor is operatively
connected to the activator such that at a pre-selected measurement,
the activator is activated thus causing the effector to activate.
In a related embodiment, the monitor is operatively connected to
the activator such that the activator can only be manually
activated by the user when the monitor measures a predetermined
measurement from the pressure transducer. In yet another related
embodiment, the monitor does not affect the operability of the
activator.
[0054] In yet another embodiment, the pressure transducer may
respond to deflection by varying capacitance rather than
resistance. Capacitance can be varied by sandwiching a pressure
sensitive dielectric material between two electrodes.
Alternatively, changes in pressure can be measured by varying
inductance with inductor transducer device 90 illustrated in FIG.
90. As seen, the device includes a cap 94 which can move in an
axial direction (the direction of arrow 100) toward and away from
the relaxed (no-pressure) position shown in the figure, mounted for
such axial movement on a support 92 which is carried on the distal
end of the apparatus tool. The support provides an induction coil
99 formed of conductive wire windings 98 which are positioned
adjacent a cylindrical permanent magnet 96 mounted on the cap.
[0055] Movement of the cap in the direction of arrow 100 caries
magnet 96 past the inductive wires, producing a change in the
inductance of the coil. Such changes can be monitored by
incorporating the inductor into a LC or inductor-capacitor
oscillating circuit and monitoring the change in the resonant
frequency of the LC circuit.
[0056] In yet another embodiment, any transducer described herein
may be combined with an ultrasonic transducer capable of detecting
tissue density or thickness. For example, the ultrasonic transducer
of Zanelli, et al., U.S. Pat. No. 6,024,703, herein incorporated in
its entirety by reference, discloses an ultrasound device for axial
ranging. This would provide for the ability to limit the throw or
depth that an effector element is permitted to penetrate into the
patient tissue underlying the tissue surface thus avoiding either
to shallow, thus ineffective penetration, or to deep and thus
harmful penetration of the effector element.
[0057] As should be apparent from the foregoing description, the
present invention, unlike fluoroscopic methods provides force
information such as but not limited to, force contact, magnitude
and direction or incident angle with respect to the patient tissue
surface, for catheter-based surgical procedures or other medical
procedures where the degree of contact between the medical
instrument and a surface of an anatomical structure is useful to
know. In addition, such information may be provided in real-time
and in a variety of formats using a low cost, disposable force
contact transducer of the type disclosed herein. Such a transducer
may be easily integrated into existing catheter tools, eliminating
the need for extensive hardware/software interfaces.
[0058] While various embodiments of the invention have been
illustrated and described, it will be evident to those skilled in
the art in light of the foregoing disclosure that many further
alternatives, modifications and variations are possible. For
example, the insulator need not be a separate element but may be in
the form of an insulative coating that is selectively applied to
the conductive surface of the flange to permit the lower surface of
the conductive elastomer to make contact with that conductive
surface in accordance with the teachings of the invention. The
invention disclosed herein is intended to embrace all such
alternatives, modifications, and variations as may fall within the
spirit and scope of the appended claims.
* * * * *