U.S. patent application number 11/158259 was filed with the patent office on 2007-01-04 for aspiration control via flow or impedance.
Invention is credited to Shawn X. Gao, Mark A. Hopkins, John C. Huculak, Nader Nazarifar, Roger Thomas, Kirk W. Todd.
Application Number | 20070005030 11/158259 |
Document ID | / |
Family ID | 38282442 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070005030 |
Kind Code |
A1 |
Hopkins; Mark A. ; et
al. |
January 4, 2007 |
Aspiration control via flow or impedance
Abstract
A microsurgical system capable of controlling aspiration and
detecting an occlusion via monitoring a change in either suction
flow rate or suction impedance.
Inventors: |
Hopkins; Mark A.; (Mission
Viejo, CA) ; Huculak; John C.; (Mission Viejo,
CA) ; Todd; Kirk W.; (Yorba Linda, CA) ;
Thomas; Roger; (Tustin, CA) ; Gao; Shawn X.;
(Irvine, CA) ; Nazarifar; Nader; (Laguna Niguel,
CA) |
Correspondence
Address: |
ALCON
IP LEGAL, TB4-8
6201 SOUTH FREEWAY
FORT WORTH
TX
76134
US
|
Family ID: |
38282442 |
Appl. No.: |
11/158259 |
Filed: |
June 21, 2005 |
Current U.S.
Class: |
604/317 |
Current CPC
Class: |
A61M 1/743 20210501;
A61M 1/804 20210501; A61M 1/732 20210501; A61M 2205/3379 20130101;
A61M 2205/123 20130101; A61M 1/74 20210501 |
Class at
Publication: |
604/317 |
International
Class: |
A61M 1/00 20060101
A61M001/00 |
Claims
1. Apparatus for controlling aspiration in a microsurgical system,
comprising: a pressurized gas source; a vacuum generator fluidly
coupled to said pressurized gas source; an aspiration chamber
fluidly coupled to said pressurized gas source and said vacuum
generator; a fluid level sensor operatively coupled to said
aspiration chamber; a pump fluidly coupled to said aspiration
chamber; a proportional controller; and a computer electrically
coupled to said fluid level sensor, said pump, and said
proportional controller; whereby upon selection of a desired
suction flow rate for said aspiration chamber via said proportional
controller, said fluid level sensor determines an actual fluid
level in said aspiration chamber and provides a signal
corresponding to said determined fluid level to said computer, and
said computer calculates a suction flow rate in response to said
determined fluid level and monitors a change in said suction flow
rate to detect an occlusion.
2. The apparatus of claim 1 wherein said computer adjusts a
surgical parameter of said apparatus in response to said
occlusion.
3. The apparatus of claim 2 wherein said surgical parameter is
selected from the group consisting of ultrasound energy, desired
suction flow rate, desired suction pressure, infusion pressure, cut
rate, and port open duty cycle.
4. The apparatus of claim 1 further comprising a surgical device
for aspirating tissue fluidly coupled to said aspiration chamber,
and wherein said computer adjusts a surgical parameter of said
device in response to said occlusion.
5. The apparatus of claim 1 wherein said vacuum generator is a
vacuum chip.
6. The apparatus of claim 1 wherein said vacuum generator is a
venturi chip.
7. The apparatus of claim 1 wherein said pump is a peristaltic
pump.
8. The apparatus of claim 1 wherein said microsurgical system is an
ophthalmic microsurgical system.
9. A method of controlling aspiration in a microsurgical system,
comprising the steps of: creating a desired suction flow rate in an
aspiration chamber using a pressurized gas source, a vacuum
generator, and a pump; aspirating fluid from a surgical device into
said aspiration chamber; determining an actual level of said fluid
in said aspiration chamber; calculating a suction flow rate in
response to said actual level of fluid; and monitoring a change in
said suction flow rate to detect an occlusion.
10. The method of claim 9 further comprising the step of adjusting
a surgical parameter of said apparatus in response to said
monitoring step.
11. The method of claim 10 wherein said surgical parameter is
selected from the group consisting of ultrasound energy, desired
suction flow rate, desired suction pressure, infusion pressure, cut
rate, and port open duty cycle.
12. The method of claim 9 further comprising the step of adjusting
a surgical parameter of said device in response to said monitoring
step.
13. Apparatus for controlling aspiration in a microsurgical system,
comprising: a pressurized gas source; a vacuum generator fluidly
coupled to said pressurized gas source; an aspiration chamber
fluidly coupled to said pressurized gas source and said vacuum
generator; a fluid level sensor operatively coupled to said
aspiration chamber; a pump fluidly coupled to said aspiration
chamber; a proportional controller; and a computer electrically
coupled to said fluid level sensor, said pump, and said
proportional controller; whereby upon selection of a desired
suction flow rate for said aspiration chamber via said proportional
controller, said fluid level sensor determines an actual fluid
level in said aspiration chamber and provides a signal
corresponding to said determined fluid level to said computer, and
said computer: calculates a suction flow rate in response to said
determined fluid level; calculates a suction impedance in response
to said suction flow rate; and monitors a change in said suction
impedance to detect an occlusion.
14. The apparatus of claim 13 wherein said computer adjusts a
surgical parameter of said apparatus in response to said
occlusion.
15. The apparatus of claim 14 wherein said surgical parameter is
selected from the group consisting of ultrasound energy, desired
suction flow rate, desired suction pressure, infusion pressure, cut
rate, and port open duty cycle.
16. The apparatus of claim 13 further comprising a surgical device
for aspirating tissue fluidly coupled to said aspiration chamber,
and wherein said computer adjusts a surgical parameter of said
device in response to said occlusion.
17. The apparatus of claim 13 wherein said vacuum generator is a
vacuum chip.
18. The apparatus of claim 13 wherein said vacuum generator is a
venturi chip.
19. The apparatus of claim 13 wherein said pump is a peristaltic
pump.
20. The apparatus of claim 13 wherein said microsurgical system is
an ophthalmic microsurgical system.
21. The apparatus of claim 16 wherein said computer communicates a
tissue property to a surgeon in response to said suction
impedance.
22. A method of controlling aspiration in a microsurgical system,
comprising the steps of: creating a desired suction flow rate in an
aspiration chamber using a pressurized gas source, a vacuum
generator, and a pump; aspirating fluid from a surgical device into
said aspiration chamber; determining an actual level of said fluid
in said aspiration chamber; calculating a suction flow rate in
response to said actual level of fluid; calculating a suction
impedance in response to said suction flow rate; and monitoring a
change in said suction impedance to detect an occlusion.
23. The method of claim 22 further comprising the step of adjusting
a surgical parameter of said apparatus in response to said
monitoring step.
24. The method of claim 23 wherein said surgical parameter is
selected from the group consisting of ultrasound energy, desired
suction flow rate, desired suction pressure, infusion pressure, cut
rate, and port open duty cycle.
25. The method of claim 22 further comprising the step of adjusting
a surgical parameter of said device in response to said monitoring
step.
26. The method of claim 22 further comprising the step of
communicating a fluid property to a surgeon in response to said
suction impedance.
Description
FIELD OF THE INVENTION
[0001] The present invention generally pertains to controlling
aspiration in microsurgical systems and more particularly to
controlling aspiration in ophthalmic microsurgical systems.
DESCRIPTION OF THE RELATED ART
[0002] During small incision surgery, and particularly during
ophthalmic surgery, small probes are inserted into the operative
site to cut, remove, or otherwise manipulate tissue. During these
surgical procedures, fluid is typically infused into the eye, and
the infusion fluid and tissue are aspirated from the surgical site.
Varying surgical conditions and surgical objectives can lead to
varying amounts of effort required to effectively and safely remove
the tissue and fluid.
[0003] The types of aspiration systems used, prior to the present
invention, were generally characterized as either flow controlled
or vacuum controlled, depending upon the type of pump used in the
system. Each type of system has certain advantages.
[0004] Vacuum controlled aspiration systems are operated by setting
a desired vacuum level, which the system seeks to maintain. Flow
rate is dependent on intraocular pressure, vacuum level, and
resistance to flow in the fluid path. Actual flow rate information
is unavailable. Vacuum controlled aspiration systems typically use
a venturi or diaphragm pump. Vacuum controlled aspiration systems
offer the advantages of quick response times, control of decreasing
vacuum levels, and good fluidic performance while aspirating air,
such as during an air/fluid exchange procedure. Disadvantages of
such systems are the lack of flow information resulting in
transient high flows during phacoemulsification or fragmentation
coupled with a lack of occlusion detection. Vacuum controlled
systems are difficult to operate in a flow controlled mode because
of the problems of non-invasively measuring flow in real time.
[0005] Flow controlled aspiration systems are operated by setting a
desired aspiration flow rate for the system to maintain. Flow
controlled aspiration systems typically use a peristaltic, scroll,
or vane pump. Flow controlled aspiration systems offer the
advantages of stable flow rates and automatically increasing vacuum
levels under occlusion. Disadvantages of such systems are
relatively slow response times, undesired occlusion break responses
when large compliant components are used, and vacuum can not be
linearly decreased during tip occlusion. Flow controlled systems
are difficult to operate in a vacuum controlled mode because time
delays in measuring vacuum can cause instability in the control
loop, reducing dynamic performance.
[0006] One currently available ophthalmic surgical system, the
MILLENIUM system from Storz Instrument Company, contains both a
vacuum controlled aspiration system (using a venturi pump) and a
separate flow controlled aspiration system (using a scroll pump).
The two pumps can not be used simultaneously, and each pump
requires separate aspiration tubing and cassette.
[0007] Another currently available ophthalmic surgical system, the
ACCURUS.RTM. system from Alcon Laboratories, Inc., contains both a
venturi pump and a peristaltic pump that operate in series. The
venturi pump aspirates material from the surgical site to a small
collection chamber. The peristaltic pump pumps the aspirate from
the small collection chamber to a larger collection bag. The
peristaltic pump does not provide aspiration vacuum to the surgical
site. Thus, the system operates as a vacuum controlled system.
[0008] Accordingly, a need continues to exist for an improved
method of effectively and safely removing aspirated tissue and
fluid in a microsurgical system.
SUMMARY OF THE INVENTION
[0009] The present invention is a method of controlling aspiration
in a microsurgical system. A desired suction flow rate is created
in an aspiration chamber using a pressurized gas source, a vacuum
generator, and a pump. Fluid is aspirated from a surgical device
into the aspiration chamber. An actual level of the fluid is
determined in the aspiration chamber.
[0010] In one aspect of the present invention, a suction flow rate
is calculated in response to the actual level of fluid. A change in
the suction flow rate is monitored to detect an occlusion.
[0011] In another aspect of the present invention, a suction
impedance is calculated in response to the suction flow rate. A
change in the suction impedance is monitored to detect an
occlusion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the present invention,
and for further objects and advantages thereof, reference is made
to the following description taken in conjunction with the
accompanying drawing, in which FIG. 1 is a schematic diagram
illustrating aspiration control in a microsurgical system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The preferred embodiment of the present invention and its
advantages is best understood by referring to FIG. 1 of the
drawings. Microsurgical system 10 includes a pressurized gas source
12, an isolation valve 14, a vacuum proportional valve 16, an
optional second vacuum proportional valve 18, a pressure
proportional valve 20, a vacuum generator 22, a pressure transducer
24, an aspiration chamber 26, a fluid level sensor 28, a pump 30, a
collection bag 32, an aspiration port 34, a surgical device 36, a
computer or microprocessor 38, and a proportional control device
40. The various components of system 10 are fluidly coupled via
fluid lines 44, 46, 48, 50, 52, 54, 56, and 58. The various
components of system 10 are electrically coupled via interfaces 60,
62, 64, 66, 68, 70, 72, 74, and 76. Valve 14 is preferably an
"on/off" solenoid valve. Valves 16-20 are preferably proportional
solenoid valves. Vacuum generator 22 may be any suitable device for
generating vacuum but is preferably a vacuum chip or a venturi chip
that generates vacuum when isolation valve 14 and vacuum
proportional valves 16 and/or 18 are open and gas from pressurized
gas source 12 is passed through vacuum generator 22. Pressure
transducer 24 may be any suitable device for directly or indirectly
measuring pressure and vacuum. Fluid level sensor 28 may be any
suitable device for measuring the level of a fluid 42 within
aspiration chamber 26 but is preferably capable of measuring fluid
levels in a continuous manner. Pump 30 may be any suitable device
for generating vacuum but is preferably a peristaltic pump, a
scroll pump, or a vane pump. Microprocessor 38 is capable of
implementing feedback control, and preferably PID control.
Proportional controller 40 may be any suitable device for
proportionally controlling system 10 and/or surgical device 36 but
is preferably a foot controller.
[0014] System 10 preferably utilizes three distinct methods of
controlling aspiration, vacuum control, suction control, and flow
control. In vacuum control mode, microprocessor 38 activates
isolation valve 14 via interface 66 and maintains pressure valve 20
in a closed state via interface 70. Proportional controller 40 and
microprocessor 38 are used to proportionally open or close vacuum
proportional valve 16 (and optionally vacuum proportional valve 18,
for higher levels of vacuum) via interfaces 60, 64, and 68. A
surgeon inputs a maximum vacuum level into microprocessor 38. Using
proportional controller 40, the surgeon may then proportionally
vary the desired vacuum provided to surgical device 36 and
aspiration chamber 26 via vacuum generator 22 between zero and the
maximum value. As aspiration chamber 26 fills with fluid 42
aspirated by surgical device 36, pressure transducer 24 measures
the actual vacuum in aspiration chamber 26 and provides a
corresponding signal to microprocessor 38 via interface 72.
Microprocessor 38 in turn provides feedback signals to valves 16
and 18 via interfaces 64 and 68 to maintain the vacuum at the
desired level indicated by proportional controller 40.
[0015] In the suction control mode, microprocessor 38 activates
valves 14, 16, 18, and 20. System 10 is configured to provide a
range of suction to surgical device 36 and aspiration chamber 26
from a small positive value of pressure to a larger negative value
of pressure (or vacuum). This range is preferably from about +150
mm Hg to about -650 mm Hg. Using proportional controller 40, a
surgeon may proportionally vary the desired suction provided to
surgical device 36 and aspiration chamber 26 via pressurized gas
source 12 and vacuum generator 22 in this range. A signal
corresponding to the desired suction is provided to microprocessor
38 via interface 60. Pressure transducer 24 provides a signal
corresponding to the actual suction pressure in aspiration chamber
26 to microprocessor 38 via interface 72. Microprocessor 38 then
provides feedback signals to any combination of valves 16, 18, and
20 via interfaces 64, 68, and 70, respectively, to maintain the
suction within aspiration chamber 26 and surgical device 36 at the
desired level. As one skilled in the art will appreciate, the
suction control mode allows microprocessor 38 to close valves 16
and 18 and open valve 20 to create a pressure within aspiration
chamber 26 equal to the intraocular pressure so as to prevent
passive flow from the eye into surgical device 36 and aspiration
chamber 26.
[0016] In the flow control mode, microprocessor 38 activates valves
14, 16, 18, and 20. System 10 is configured to provide a range of
flow to surgical device 36 and aspiration chamber 26 from a value
of zero flow to a maximum value of flow. Using proportional
controller 40, a surgeon may proportionally vary the desired
suction flow rate for surgical device 36 and aspiration chamber 26
in this range. Flow rate is calculated using the following
equation: Q.sub.suction=Q.sub.pump(N,P)+A dz/dt, where
Q.sub.suction is the suction flow rate, Q.sub.pump is the flow rate
of pump 30, N is the speed of pump 30, P is the suction pressure
measured by pressure transducer 24, A is the cross-sectional area
of aspiration chamber 26, and Z is the level of fluid 42 in
aspiration chamber 26 measured via fluid level sensor 28. A signal
corresponding to the desired Q.sub.suction is provided to
microprocessor 38 via interface 60. Microprocessor 38 provides a
signal corresponding to pump speed N to pump 30 via interface 74 in
response to the desired Q.sub.suction. Fluid level sensor 28
provides a signal corresponding to the actual level of fluid within
aspiration chamber 26 to microprocessor 38 via interface 76.
Microprocessor 38 uses the suction control mode, as described
above, to maintain Q.sub.suction at the desired level. More
specifically, microprocessor 38 calculates Q.sub.suction in
response to the actual level of fluid within aspiration chamber 26
and provides feedback signals to any combination of valves 16, 18,
and 20 via interfaces 64, 68, and 70, respectively, so as to
maintain Q.sub.suction at the desired level. As part of the suction
control mode, pressure transducer 24 provides a signal
corresponding to the actual suction pressure P in aspiration
chamber 26 to microprocessor 38 via interface 72. As one skilled in
the art will appreciate, the flow control mode allows
microprocessor 38 to maintain a constant level of fluid 42 in
aspiration chamber 26 (dz/dt=0) so as to maintain flow rate.
[0017] In the suction control mode, suction impedance can be
defined as follows:
I=(P.sub.suction-P.sub.reference)/Q.sub.suction, where I is the
suction impedance, Q.sub.suction is the suction flow rate,
P.sub.suction is the suction pressure P measured by pressure
transducer 24, and P.sub.reference is a reference pressure, such as
intraocular pressure in an aspiration circuit of a microsurgical
system, or infusion pressure, irrigation pressure, or atmospheric
pressure in the infusion circuit of a microsurgical system. As
discussed hereinabove, traditional vacuum controlled aspiration
systems are not capable of occlusion detection in the aspiration
circuit, and traditional flow based aspiration systems detect
occlusion in the aspiration circuit by monitoring change in
measured vacuum. It has been discovered that monitoring change in
Q.sub.suction or I is a more effective and safe way of detecting
occlusion in an aspiration circuit of a microsurgical system.
Detecting occlusion by monitoring change in Q.sub.suction or I
gives a surgeon a better idea of the characteristics of the
material that is causing the occlusion. Monitoring change in I is
believed to be preferred over monitoring change in Q.sub.suction.
Preferably, microprocessor 38 monitors such change in Q.sub.suction
or I in real time.
[0018] Once an occlusion is detected by monitoring change in
Q.sub.suction or I, microprocessor 38 may automatically adjust
other surgical parameters in order to improve the speed and safety
of the surgical procedure. For example, if surgical device 36 is a
phacoemulsification probe, ultrasound energy, desired suction
pressure, desired suction flow rate, and/or infusion pressure may
be adjusted real-time as either Q.sub.suction or I changes. As
another example, if surgical device 36 is a vitrectomy probe, cut
rate, port open duty cycle, desired suction pressure, desired
suction flow rate, and/or infusion pressure may be adjusted real
time as either Q.sub.suction or I changes. In addition,
microprocessor 38 may use changes in I to communicate fluid or
tissue properties such as viscosity to the surgeon via an
appropriate sense (e.g. audibly, visually, or tactilely).
[0019] The present invention is illustrated herein by example, and
various modifications may be made by a person of ordinary skill in
the art. For example, while the present invention is described
above relative to detecting occlusion in the aspiration circuit of
a microsurgical system, it is also applicable to detecting
occlusion in the infusion circuit of a microsurgical system.
[0020] It is believed that the operation and construction of the
present invention will be apparent from the foregoing description.
While the apparatus and methods shown or described above have been
characterized as being preferred, various changes and modifications
may be made therein without departing from the spirit and scope of
the invention as defined in the following claims.
* * * * *