CA1068572A

CA1068572A - Flow control system

Info

Publication number: CA1068572A
Application number: CA218,129A
Authority: CA
Inventors: Steven N. Weiss; Alan Broadwin
Original assignee: Cavitron Corp
Current assignee: Cavitron Corp
Priority date: 1974-01-28
Filing date: 1975-01-17
Publication date: 1979-12-25
Also published as: US3902495A

Abstract

ABSTRACT

A fluidic control system is provided for use in irrigation and aspiration of the anterior chamber of the eye during ultrasonic fragmentation of a cataract therein. The system comprises a handpiece with an (ultrason-ically vibrated) hollow tip, the hollow tip being connected to the fluid with-drawal or aspirating portion, while an annular passage around the tip is used to introduce fluid for irrigation purposes. The aspirating portion comprises a withdrawal hose attached to the output manifold of the handpiece in fluid communication with the hollow tip, a constant flow pump attached to the other end of the withdrawal hose, and a vacuum relief valve connected to the with-drawal hose intermediate the pump and the handpiece. The irrigation portion comprises a fluid supply bottle at a predetermined height above the eye, and administration set attached to the bottle, and an inflow hose attached to the intake manifold of the handpiece and in fluid communication with the annular passage. All the aforementioned components are in fluid communication with the anterior chamber of the eye during removal of a cataract by insertion of the handpiece tip into the eye chamber.

Description

10685'72 This application relates to an improvement in the control of fluid flow in a surgical device. More particularly this invention relates to an improvement in the fluid flow systems for a surgical device useful in catar-act removal such as that shown by U.S. Patent No. 3,589,363 issued June 29, 1971 to A. Banko and C.D. Kelman for a Material Removal Apparatus and Method Employing High Frequency Vibrations. The aforesaid patent describes an in-strument for breaking apart and removing unwanted tissue and material espec-ially a cataract located in the anterior chamber of the eye by ultrasonically fragmenting the cataract while simultaneously introducing fluid into the eye chamber, and withdrawing the fluid and fragmented cataract particles. Briefly the device described includes a handpiece having an operative tip vibrating in the ultrasonic range which is also hollow and is in turn surrounded by a tubular sleeve. In operation the tip of the handpiece including the surround-ing tubular sleeve are inserted into the anterior chamber of the eye. Treat-ment fluid is introduced through the hollow sleeve at a constant low pressure.
This introduction of fluid which is called irrigation is to provide a replace-ment for fluid withdrawn or lost from the eye chamber. The withdrawal of fluid and suspended material from the anterior chamber is specifically called aspiration and ideally there is no change in fluid content or anterior cham-ber pressure as a result of irrigation-aspiration. This of course is impos-sible to achieve since aspiration is intended to remove solids which until broken up sometimes tend to occlude or block the fluid withdrawal openings of the handpiece. ~ -This problem with control of fluid content and pressure within the an~erior chamber of the eye during irrigation-aspiration is discussed in de-tail in U.S. Patent No. 3,696,613 issued September 26, 1972 to Charles Kel-man for a Surgical Handpiece and Flow Control System for Use Therewith, and commonly assigned herewith.
A handpiece described in the aforesaid U.S. Patent as well as the instrumentation described in U.S. Patent No. 3,589,363 provides a tool tip -1- ~

~06857Z
insertable in the anterior chamber of the eye with an annular nozzle for supply of fluid for irrigation, a hollow tool tip which is vibrated at about 40,000 cps to provide the energy to break up the cataract and allow fluid withdrawal for aspirating the reduced particles and fluid. When the hand-piece is inserted into the eye, it is extremely important to maintain the fluid pressure of the chamber within a certain range and to prevent rapid fluctuations of the pressure and fluid content of the chamber. A collapse of the anterior chamber for lack of sufficient pressure could result in damage to soft tissues of the eye as well as possible damage of the eye posterior capsule itself from contact of the tissues with the vibrating tool tip. This problem of maintaining the proper pressure is a particularly difficult and sensitive one and is one of the problems which the apparatus shown in the aforesaid U.S. Patent No. 3,696,613 was designed to solve. The system shown therein while satisfactory is quite obviously a rather complex apparatus which re~uires in terms of control, close and competent operation personnel.
Thus as part of the operation to remove a cataract from the anterior chamber ` of the eye the handpiece is inserted into the chamber through a small incis-ion and the fluid flow adjusted to the desired level principally by the height at which the irrigation fluid source is supported to provide a gravity flow into the eye, and the speed of a constant flow positive displacement pump in the piping from the eye to withdraw the aspirating stream. The surgeon then moves the cataract lens into the anterior chamber, applies the ultrasonic vibration to the tip of the handpiece in contact with the lens and proceeds - to break up the lens.
As part of the application of the tip to the lens the opening in ` the tip through which aspiration proceeds is periodically occluded by lens material. During such occlusion, fluid is prevented from entering the hollow tip, although the constant flow pump continues to operate. The pump oper-ation thus starts drawing a vacuum in the conduit between the handpiece tip and the pump. At the same time, the pressure from the gravity feed of irrig-', ' :

ation fluid into the eye remains constant and increases flu;d pressure in the anterior chamber of the eye, expanding it sormewhat. However once the open-ing into the handpiece tip is uncapped by fragmentation of the occlusion, the high vacuum existing in the aspirating system tends to quickly withdraw fluid from the anterior chamber. This may rapidly decompress the anterior chamber and draw the enclosing tissues towards the handpiece tip. Besides the danger represented by the ultrasonic vibrations of the handpiece tip on contact with these tissues, the rapid decompression itself may be injurious to the tissues. The apparatus shown by the aforesaid U.S. Patent No.
3,696,613 of course is designed to eliminate such perturbations to the eye by monitoring and controlling flow. It would be advantageous to have a system which is not only fail-safe by means of being simple rather than complex, but is also more easily regulated and controlled by normal operative personnel rather than trained technicians.
Accordingly the system of the invention consists of a fluid flow system for use in aspiration of a fluid from a small, pressure-responsive, fluid containing chamber such as the anterior chamber of an eye, said system comprising: fluid withdrawal duct means for aspirating said fluid from said chamber at a rate which avoids rapid pressure changes in said chamber;
aspiration suction means for providing said fluid aspiration in said fluid withdrawal duct means; and pressure responsive valve means connecting said fluid withdrawal duct means to said aspiration suction means and responsive ~ directly to the pressure in said fluid withdrawal duct means for opening to -~ atmosphere when excessive vacuum which would cause said rapid pressure changes in said chamber, and consequent excessive pressure transients therein, build-ups in said fluid withdrawal duct means.
A preferred system according to the invention comprises: a fluid source under substantially constant pressure; fluid inflow means connected ; to the fluid source for limiting flow of the fluid from the source into the chamber thereby providing irrigation fluid at a predetermined limited flow :' ~

' , , ,: :

10685~7Z
rate and pressure into the chamber; fluid withdrawal means in fluid commun-ication with the chamber for aspirating fluid from the chamber at a rate to eliminate transient pressure shocks to the chamber; a constant flow pump connected to the other end of the fluid withdrawal means, with the pump act-ing to draw fluid from the chamber through the withdrawal means; and the withdrawal means including a pressure differential relief valve intermediate the chamber and the pump, the relief valve responsively opening at a predet-ermined pressure differential which in combination with the parameters of the fluid withdrawal means limits the occurrence of pressure transients com-municated to the chamber, whereby flow resistivity of the withdrawal means between the chamber and the valve attenuates the pressure changes transmitted to the chamber when the valve opens in response to the predetermined pressure ; differential between atmosphere and the pressure in the withdrawal means reaching the predetermined differential pressure.
Preferably where the enclosed volume is the anterior chamber of the 0ye, the relief valve opens to atmosphere in response to a pressure differen-tial o from 10 mm of mercury (Hg) to 100 mm Hg; the pressure of the fluid source is in the range of from 10 to lO0 mm Hg; the flow resistivity of the inflow means is from 0.042 to 18.5 mm Hg per ml per min; the flow resistivity of the fluid withdrawal means is from 0.35 to 21.5 mm Hg per ml per min; and ; the constant flow volume of the pump is from 5 to 50 ml per min. More part-icularly the preferred pressure, flow and flow resistivity ranges of the sys-tem according to the present invention comprise the following: a fluid source exerting a constant pressure of from 30 to 60 mm Hg; the inflow means having a flow resistivity of from 0.5 to 2.5 mm Hg. ml per min between the fluid source at one end and to the operative volume of the anterior chamber of an - eye at the other end; the fluid withdrawal means having a flow resistivity of from 1.33 to 3.0 mm Hg. per ml per min. from the operative volume of the ant-erior chamber of the eye and to the atmosphere; the constant volume pump hav-ing a flow rate of from 20 to 30 ml per min; and the relief valve connected . . - :

' ~068572 to the flow withdrawal means intermediate the pump and the eye chamber res-ponsively opening the atmosphere at a pressure differential of between about 30 and 50 mm Hg.
It is therefore an object of this invention to provide a fluidic control system for use in aspirating a small elastic volumetric space.
Another object of the present invention is to provide an effective flow control system for aspirating the anterior chamber of the eye.
Yet another object of the present invention is to provide a flow ;~
control system for effectively limiting the transient pressure and flow changes as felt by the anterior chamber of the eye during irrigation and aspiration thereof.
Other objects and advantages of the system according to the present invention will be apparent from the brief description of the drawings and the preferred embodiment which follows.
Pigure 1 of the drawings is a diagram of the fluidic flow control system of the present invention; and Figure 2 of the drawings is an electrical circuit analog of the flow control system of Figure 1.
In the U.S. Patent No. 3,589,363 described hereinbefore, apparatus and method for the removal of material by employing high frequency vibration is shown and described. Briefly the aforesaid patent describes an instru-ment for breaking apart and removing unwanted material such as for surgically - removing a cataract from the eye. The apparatus includes a handpiece having an operative tip vibrating at a frequency in the ultrasonic range ~preferably about 40,000 cps) with an amplitude controllable up to several thousandths -of an inch. The operative tip is itself hollow and is in turn surrounded by a tubular slePve forming an annular passage. The inflow fluid for irrig-ating the anterior chamber of the eye is introduced into the chamber through the annular passage and the broken up material, small particles and fluid in the eye, is with~rawn at the same time through the hollow tip to aspirate ~68572 the chamber.
Referring now to Figure l of the drawings wherein a simplified diagram of a handpiece 12 is shown with an operative tip 14 having a hollow withdrawal means 16, and an annular passage 18 surrounding the tip 14 for introducing fluid into an anterior chamber 20 of an eye undergoing cataract -surgery.
A more detailed description of the handpiece 12 described above is provided in the aforesaid United States Patents No. 3,589,363 and 3,696,613 commonly assigned to the assignee herein.

,. ~

` iO68572 :
Irriga~ion fluid is introduced into the handpiece 12 via an inflow hose 22 which is connected at one end to the handpiece and at the other end to an administration set 23, that is a hose connected to an irrigation fluid supply bottle 24 suspended by an appropriate bracket tnot shown) a fixed height 'h' over the level of the handpiece and eye. The fixed height 'h' at which the fluid supply bottle is suspended acts to apply a fixed fluid pres-sure to fluid entering the hose 22 from the bottle to the eye. The selected height is such as to apply a pressure of from about 10 mm Hg to about 100 mm Hg to fluid entering the administration set and thereby furnish a fluid source having a constant preselected pressure level in relation to the hand-piece More preferably the height at which the supply bottle is suspended is such as to apply a pressure head of from 30 mm ~g to 60 mm ~Ig. According to the present invention, this is the sole means for supplying the pressure head which forces the flow of fluid from the bottle through the administra-tion set 23, the inflow hose 22 and the annular passage of the handpiece into the anterior chamber of the eye.
For purposes of this invention the pressure which is internally applied to the eye is of prime importance. For instance, as described in United States Patent No. 3,696,613, it is very important that pressure of the anterior chamber of the eye be maintained within a certsin range of values to prevent damage thereto. A collapse of the anterior chamber due to reduced pressure could result in either the iris, the endothelium layer of the cornea, or the posterior capsule as well as other soft tissue, coming in contact with the operating tip of the handpiece. This problem of main-taining the proper pressure is a particularly difficult and sensitive one in the case of an operative site such as the anterior chamber, which is con-siderably smaller in volume than the volume of fluid necessary for continu-ous irrigation and aspiration. The anterior chamber of the eye is, of course, in the same pressure related system as the apparatus of this inven-~68S72 tion. In a cataract operation, pressure transients are periodically being induced at the tip of the handpiece due to the presence of a particle or part: of the cataract. This initially prevents entry of aspirating fluid into the tip with resulting buildup of suction in the tip, and then sudden clear-ance of the occlusion blocking the handpiece tip. The apparatus shown in the United States Patent No. 3~696,613 is designed to reduce and overcome this problem and as such as effective though expensive and complicated.
Basically the present invention provides an irrigation system which limits the fluid pressure to which the anterior chamber of the eye is subject by limiting the height at which the irrigation fluid supply is main-tained in reference to the eye, and by further limiting the flow rate into the eye utilizing specified inflow means having a specified resistivity to flow, as well as relating the irrigation system to the fluid withdrawal or aspiration system. That portion of the fluidic system co~prising the fluid withdrawal mesns, the constant flow pump ant the differential pressure relief valve act in combination to limit fluid flow from the eye, and more import-antly p~event sudden pressure changes or pressure transients from occuring -~
by increasing the time period over which the pressure changes occur and by limiting the maximum pressure drop to which the eye would be exposed. This is accomplished by controlling the constant flow rate of the pump; by setting a predetermined limit to the pressure differential, the relief valve will open to atmosphere; and by controlling the flow resistivity of the fluid withdrawal piping as herein described.
Referring back to Figure 1 of the drawing the operative tip 14 of the handpiece is hollow and has an internal fluid withdrawal passage 30 con-stituting part of the fluid withdrawal system of the present invention util-ized in aspirating the operative site of the eye. A fluid withdrawal pipe 32 is connected to the handpiece at one end and is in fluid communication with the fluid withdrawal passage. The other end of the fluid withdrawal pipe is connected to a constant flow pump 34 preferably a constant displace-' ~ 8 -: .

` tO68572 `:
ment, variable speed, peristaltic pump The peristaltic feature acts to avoid any contact of the operating parts with the withdrawn fluid suspension. -Intermediate the pump 34 and the handpiece, a relief valve 36 is connected by a T joint 38 to the fluid withdrawal pipe and is set to open to atmosphere should the pressure differential in the fluid withdrawal pipe exceed a pred-etermined pressure, which pressure may be from 30 mm ~g to 50 mm Hg Pref-erably the pressure differential at which the relief valve opens is a pres-sure of about 40 mm Hg. Constant flow capacity of the pump is preferably a flow of from about 20 ml per min to 30 ml per minute. Flow resistivity of the fluid withdrawal means at these preferred conditions is from about 1.33 mm Hg to about 3.0 mm Hg. Flow resistivity in the fluid inflow system is on the order of from about 0.5 to about 2.5 mm Hg per ml per min.
We have therefore described an effective, economical system for irrigating and aspirating the anterior chamber of the eye during an operation involving the insortion of a handpiece through a small incision in the eye and during which parts of the eye such as a cataract are reduced by the action of an ultrasonically vibrating tip. With reference to further understanding its operation, reference is now made to Figure 2 of the drawing which shows the electrical analogue circui* which led to the fluidic control system of this invention. It must be further understood that each part of the inven-,~
tion functions in relation to a moderately uncontrollable set of conditions imposed by the needs of the operative site, i.e., anterior chamber of humaD
eye and the size of the operative incision. The conditions in the anterior chamber of the eye are analogized by two electrical elements which are a resistive element 44 to account for flow reslstivity through the incision, ;~
and a capacitor 45 to correspond to elasticity of the eye chamber, both ele-ments being in parallel and connected to ground at one end and at the other end to the inflow irrigation system and the fluid withdrawal system. The fluid inflow system is analogized by a constant voltage source 46 correspond-ing to the fluid supply bottle set at a specified height to provide a con--- g _ ~068572 stant pressure head; administration set resistance 47 corresponding to the flow resistivity thereof; an inflow resistance 48 corresponding to flow res-istivity of the inflow hosing, and a resistance 50 corresponding to the flow resistivity of the fluid inflow manifold of the handpiece. For the fluid withdrawal system a pipe resistance 52 corresponds to the resistivity imposed in the fluid withdrawal piping, and the handpiece by outflow manifold res-istance 54.
The relief valve is analogized by a diode 56 and a zener diode 58 back to back in series at one end to the fluid withdrawal pipe and at the other end to ground (or atmosphere) The constant flow pump is analogized by inserting a hypothetical electrical current element 60 acting as a constant current source. In terms of the electrical analogues of the fluidic para-meters-resistance (R~ is equivalent to flow resistance in pressure terms;
voltage (V) is equivalent to a pressure source in mm Hg; and current amperes (I) is equivalent to flow in ml per min. Utilizing the above analogy, the present invention has been conceived and built and various known conditions have been related in determining the operative parameters which are described ; hereinbefore.
The system is able to accomplish the irrigation-aspiration of the anterior chamber of the eye, while at the same time reducing transients in-troduced by occlusions of the fluid withdrawal or aspirating system. It can be seen that by the invention, a simplified though quite effective fluidic control system has been provided for use in conjunction with the operative ; system described herein and in the a~oresaid United States Patent No. 3,589, 3~3 and which provides the safeguards, effectiveness, ease of use, and oper-ative usefulness desired by the system shown in United States Paten~ No.
3,696,613.
The invention may be employed with certain modifications and var-iations. For instance, the irrigation portion of the system may be employed without the aspiration system. In this mode of employment flow of fluid into 1~68572 ~
the eye is as previously described while flow of fluid out of the anterior chamber of the eye is through the opening or incision made therein for the insertion of the handpiece tip. A modification of the irrigation system is shown in the drawings where a pressure means for relief of undue pressure head is employed. The pressure means comprises a pressure relief valve 39 connected to the inflow hose 22 by a tube 40. The pressure relief valve 39 is selected to prevent undue pressure from being applied through the irrig-ation system to the eye chamber. The analogous components shown in Figure

2 of the drawings to such a pressure relief means incorporated in the irrig-- 10 ation system comprise a diode 62 connected to the circuit between resistors 48 and 50 and a zener diode 64 connected back to back with the diode 62. The zener diode anod0 is connected to ground ~atmosphere). By this variation we are able to further limit the pressure which can be communicated to the eye chamber through the irrigation system.

- 1 1 ~

j .

Claims

THE EBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fluid flow system for use in the aspiration of a fluid from a small, pressure-responsive, fluid-containing chamber such as the anterior chamber of an eye, said system comprising: fluid withdrawal duct means for aspirating said fluid from said chamber at a rate which avoids rapid pressure changes in said chamber; aspiration suction means for providing said fluid aspiration in said fluid withdrawal duct means; and pressure-responsive valve means connecting said fluid withdrawal duct means to said aspiration suction means and responsive directly to the pressure in said fluid withdrawal duct means for opening to atmosphere when excessive vacuum which would cause said rapid pressure changes in said chamber, and consequent excessive pressure transients therein, build-ups in said fluid withdrawal duct means.

2. A system according to claim 1, wherein said chamber is the anterior chamber of an eye and said rapid pressure changes in said eye chamber are such as would rapidly collapse said eye chamber by aspirating substantially all the fluid therein through said fluid withdrawal duct means or produce such pressure transients as would damage said eye chamber.

3. A system according to claims 1 or 2; and further comprising irrigation means for providing an irrigation fluid to said chamber at a rate generally corresponding to said rate at which said fluid withdrawal duct means aspirates said first-named fluid from said chamber.

4. A system according to claim 1, wherein said fluid withdrawal duct means has a flow resistivity of from about 0.35 to 21.5 mm Hg per ml per min, said aspiration suction means is a constant flow pump having a flow rate of from about 5 to 50 ml per min and said pressure-responsive valve means opens to atmosphere at a pressure differential between the pressure in said fluid withdrawal duct means and atmosphere of between about 10 and 100 mm Hg.

5. A system according to claim 4; and further comprising irrigation means for providing an irrigation fluid to said chamber, said irrigation means comprising a source of said irrigation fluid at a pressure of from about 10 to 100 mm Hg and means connecting said irrigation fluid source to said chamber and having a flow resistivity of from about 0.42 to 18.5 mm Hg per ml per min for conducting said irrigation fluid to said chamber.

6. A system according to claim 5, wherein said pressure of said irrigation fluid in said source is about 45 mm Hg, the pressure-responsive valve means opens at a pressure differential of about 40 mm Hg, said pump has a flow rate of about 25 ml per min, said means for conducting said irrigation fluid to said chamber has a flow resistivity of about 1.06 mm Hg per ml per min and said fluid withdrawal means has a flow resistivity of about 1.57 mm Hg per ml per min.

7. A system according to claim 5, wherein said pressure of said irrigation fluid in said source is in a range of about 30 to 60 mm Hg, said means for conducting said irrigation fluid to said chamber has a flow resistivity of from about 0.5 to 2.5 mm Hg per ml per min, said fluid with-drawal means has a flow resistivity of from about 1.33 to 3.0 mm Hg per ml per min, said pump has a flow rate of from about 20 to 30 ml per min, and said pressure-responsive valve means opens at a pressure differential between about 30 and 50 mm Hg.

8. A system according to claim 7; and further comprising: a handpiece having an inflow manifold therethrough defining at least an irrigation-fluid output portion of said means for conducting said irrigation fluid to said chamber, and a hollow tip on a distal portion of said handpiece for insertion into said chamber, said hollow tip defining at least an input portion of said fluid withdrawal duct means; and means connected to said hollow tip remote from said distal portion for ultrasonically vibrating said hollow tip.

9. A system according to claim 1; and further comprising: a handpiece having an inflow manifold therethrough defining at least an irrigation-fluid output portion of said means for conducting said irrigation fluid to said chamber, and a hollow tip on a distal portion of said handpiece for insertion into said chamber, said hollow tip defining at least an input portion of said fluid withdrawal duct means.

10. A system according to claim 9, and further comprising: means connected to said hollow tip remote from said distal portion for ultra-sonically vibrating said hollow tip.