Title:
METHOD AND APPARATUS FOR AUTOMATIC PERITONEAL DIALYSIS
United States Patent 3709222


Abstract:
A method and apparatus for automatic peritoneal dialysis which includes a series of steps for the exchange of dialysate which proportions the in-flow to the out-flow and provides for the elimination of any distressing in-flow or out-flow pressures on the patient and any abnormal build-up of fluid quantity in the patient. The apparatus includes a portable bed-side unit which carries the necessary pumps and valves for the automatic cycle and includes a disposable plastic sheet unit supported on the apparatus which is positioned such that pumps and valves in the apparatus can operate on this unit when in place.



Inventors:
DE VRIES J
Application Number:
05/101636
Publication Date:
01/09/1973
Filing Date:
12/28/1970
Assignee:
SARNS INC,US
Primary Class:
Other Classes:
417/395, 604/29
International Classes:
A61M1/28; A61M1/00; A61M1/16; (IPC1-7): A61M5/00
Field of Search:
128/213,214R,214B,214F,214.2,230 137
View Patent Images:
US Patent References:
3620215APPARATUS FOR PERITONEAL DIALYSIS1971-11-16Tysk et al.
3545438INTERMITTENT DIALYSIS METHOD AND APPARATUS THEREFOR1970-12-08DeVries
3328255Method and apparatus for treating blood1967-06-27Ilg
3291151Fluid exchange system1966-12-13Loken
3256883Oxygenator with heat exchanger1966-06-21DeWall
3054401Transfusion set1962-09-18Gewecke
2950396N/A1960-08-23Schneider
2865388Liquid mixing and proportioning device1958-12-23Sternbergh
2625933Blood transfer mechanism1953-01-20Salisbury



Primary Examiner:
Truluck, Dalton L.
Claims:
What is claimed as new is as follows

1. A method of automatic cycling of peritoneal dialysis which comprises:

2. A method as defined in claim 1 which includes interposing a third expansible-contractible container between the first container and the patient, and positioning the third container relative to the patient to cause gravity flow of dialysate from the third container to the patient.

3. A method as defined in claim 1 which includes interposing a return chamber between the patient and the second chamber, moving dialysate from the patient to the return chamber, and subsequently moving dialysate from the return chamber to the second chamber.

4. A method as defined in claim 2 which includes interposing a return chamber between the patient and the second chamber, moving dialysate from the patient to the return chamber, and subsequently moving dialysate from the return chamber to the second chamber.

5. A method as defined in claim 1 which includes providing a waste receptacle, and intermittently discharging returned dialysate to said waste chamber from said second chamber subsequent to introduction of the said dialysate into the second chamber.

6. An apparatus for automatic cycling of peritoneal dialysis which comprises:

7. An apparatus as defined in claim 6 in which:

8. An apparatus as defined in claim 6 in which:

9. An apparatus as defined in claim 8 in which said third means includes:

10. An apparatus as defined in claim 6 in which said second means includes:

11. An apparatus as defined in claim 10 in which said pump is a peristaltic pump having a positive displacement and a negative displacement cycle sequentially, and said pressure relief means comprises a collapsible envelope in said line leading from said first means.

12. An apparatus as defined in claim 6 in which:

13. An apparatus as defined in claim 6 in which said support includes a first panel, and said containers are formed from overlaid sheets of plastic supported on said panel and heat sealed in defined areas to form said containers.

14. An apparatus as defined in claim 13 in which a plurality of collapsible connector lines are heat sealed into said plastic sheets to provide flow lines for said apparatus.

15. An apparatus as defined in claim 14 in which a plurality of valve means are supported on said panel operable to squeeze said connector lines to a close-off position.

16. An apparatus as defined in claim 15 in which a cover panel overlies said panel, and said valves operate to squeeze said connector lines against said cover panel to achieve a close-off of said connector lines.

17. An apparatus as defined in claim 13 in which said fixed volumetric chamber is formed by a predetermined area of said panel, and a relatively rigid cover portion overlying said area.

18. An apparatus as defined in claim 7 in which said relief chamber is mounted on vertically adjustable means on said support to permit regulation of hydrostatic position relative to a supply of fresh dialysate.

19. An apparatus as defined in claim 8 in which said support comprises adjustable panel means for confining the walls of said return chamber to regulate its expansion as a control means in the cycling.

20. An apparatus as defined in claim 13 in which:

21. An apparatus as defined in claim 11 in which said pump has a plurality of rollers spaced circumferentially to provide a positive displacement cycle during only a portion of the rotative cycle of said pump.

Description:
This invention relates to a Method and Apparatus for Automatic Peritoneal Dialysis.

It is an object of the present invention to provide a system and apparatus for use in peritoneal dialysis which requires a minimum of attention by skilled hospital personnel and which has a number of safety features relative to the elimination of infection and discomfort.

It is an object of the invention to provide a system and apparatus which will maintain fluid balance to monitor the amount of fluid administered to the patient, thus preventing a build-up of the fluid quantity over a period of operation.

It is a further object to provide a system which can be automatically cycled and which will warm the dialysate to maintain a certain temperature range when additional dialysate is added to the quantity in use.

It is a further object to provide a system which prevents continuing operation in the event of a negative pressure build-up in the outflow and also a system which will control maximum volume in the cycle and interrupt the cycle if a fluid source is exhausted.

The invention also contemplates the use of a disposable bag element in cooperation with a support apparatus which is relatively inexpensive compared to the overall apparatus and which permits a fresh series of chambers to be used for each patient.

Another object of the invention is a mounting apparatus for the various elements of the system which adapts itself to and cooperates with the disposable elements.

Other objects and features of the invention relating to details of construction and operation will be apparent in the following description and claims in which the principles of the invention are set forth in connection with the best mode presently contemplated for the invention.

DRAWINGS accompany the disclosure and the various views thereof may be briefly described as:

FIG. 1, a perspective view of the system showing the apparatus and the relationship to the patient.

FIG. 2, a sectional view taken on line 2--2 of FIG. 4 of the support cabinet showing the manner in which the mechanically operated valves are related to the system.

FIG. 3, a rear elevation of the valve mechanism.

FIG. 4, a view of the support apparatus cabinet with the door in open position.

FIG. 5, a view of certain disposable portions of the apparatus separated from the supporting cabinet.

FIGS. 6, 7, 8, and 9, partial sectional views taken on lines 6--6, 7--7, 8--8, and 9--9 of FIG. 5.

FIG. 10, a view of a waste bag element for the system.

FIG. 11, a sectional view on line 11--11 of FIG. 10.

FIG. 12, a view of the opening of the neck portion of the waste bag in closed position.

FIG. 13, a sectional view on line 13--13 of FIG. 12.

FIG. 14, a sectional view of the apparatus showing the return chamber of the system and associated control elements.

FIG. 15, a sectional view of the proportioning chamber of the system in relation to the controlling portions of the support apparatus.

FIG. 16, a sectional view taken on line 16--16 of FIG. 4 of a portion of the apparatus showing a sensor control switch.

FIG. 17, a sectional view on line 17--17 of FIG. 4 of a second sensing switch and response portion of the apparatus.

FIG. 18, an elevation of a peristaltic pump utilized in the system.

FIGS. 19, 20, and 21, sectional views taken on lines 19--19, 20--20, and 21--21 of FIG. 18.

FIG. 22, a diagrammatic view illustrating the system disposed for flow of fluid to the patient.

FIG. 23, another diagrammatic view showing the condition of fluid return from the patient.

FIG. 24, a view of a float valve with an orifice leak by-pass.

FIG. 25, an electrical diagram showing various control elements of the system.

REFERRING TO THE DRAWINGS

In FIG. 1, the apparatus is shown adjacent a hospital bed 30 on which is resting a patient 32 who has received the insertion of an abdominal catheter 34 leading from the apparatus. The apparatus consists of a main cabinet 36 having a door 38 which is hinged to be moved to an open position.

Cross-wise of the cabinet 36 on one end is an open topped case 40. A frame formed by cross members 41 and axles 42 and 44 is supported on wheels or castors 46 and 48. A control panel 50 is mounted on the top of the cabinet. On the side of the cabinet 36 mounted in suitable brackets 51 is a stanchion tube 52 which extends upwardly to hold two horizontal cross bars 54 and 56 which can support a supply of sterile dialysate in vessels 58 and 60. Mounted on the stanchion tube 52 is a slide bracket 61 which supports a vertical rod 62 shiftable from the solid line position shown in FIG. 1 to a dotted line position also shown wherein a horizontal portion 64 of the rod can support a plastic relief chamber bag 66 forming part of the system.

Valves which open and close certain tubes of the system, as will be later described, are shown in cross-section in FIG. 2. These are mounted on a panel 70 lying behind the door 38 of the cabinet on a bracket 72 (see FIG. 3), this bracket having a horizontal plate 74 which supports a motor 76 which drives a reduction gear 78 leading to an eccentric driven crank 80. This crank moves a plunger 82 forward and aft, the plunger being sealed by a grommet 84 in the wall of the plate 70. The plunger has a chamfered nose portion 86 which can drive forward against the door plate 38 to close off a particular tube in the system. Suitable control elements for the motor will actuate these valves in response to the general system. There are four such valve control units mounted on plate 70 and viewing FIG. 4 these are referenced as V-1, V-2, V-4 and V-5. The functions of these valves in connection with the system will be described relative to certain tubes in the system at the appropriate time.

Other hardware on the cabinet includes, as illustrated in FIG. 4, two rotating peristaltic pumps indicated generally at 90 and 92. Except as will be later described, these are of standard construction and are driven by suitable motors mounted in the cabinet 36 behind the panel 70. Additional structure is shown in the sectional view of FIG. 14 where it will be seen that at the bottom portion of the plate 70 is a recess 94 which is closed by a swinging panel 96 hinged at 98.

Behind this panel is a micro-switch actuator roller 100 on arm 102 connected with micro-switch 104. The door 38 has an opening 106 (see FIGS. 4 and 14) which also is closed by a swinging panel 108 hinged at 110. The position of the plate 108 can be adjustably regulated by an adjustment screw 112 on bracket 114. The purpose of this compartment between plates 96 and 108 will be described later.

Another compartment that is formed in the system by a portion of plate 70 and the cover 38 is shown in cross-section in FIG. 15. Plate 70 is again apertured and this aperture is provided with a shaped panel member 116 which is dished as shown in the drawing. On the back of this dished member is a small electric heater 118 which will be used to maintain a temperature level of liquid in the system. The door panel 38 is also provided with a recess which is filled by a dished member 120 essentially symmetrical with the member 116 to provide an elongate substantially rectangular, rigid-walled compartment. At the lower central portion of the plate 70, as viewed in FIG. 4, is an opening 130 shown in FIG. 17 below which is a bracket having a horizontal plate 132 on the left side and a horizontal plate 134 at a slightly higher level on the right side as viewed in FIG. 17. Positioned at the opening 130 on bracket plate 132 is a micro-switch arm 136 which controls a micro-switch 138. The purpose of this micro-switch in conjunction with the fluid system will be described later.

At the upper left-hand corner of the plate 70 is an opening 140 (FIG. 16) below which is mounted a bracket plate 142 supporting a micro-switch 144 operated by a switch arm 146. This switch arm is influenced by the pocket 224 (FIGS. 5 and 7) to reflect absence of hydraulic head in the supply line from containers 58, 60. It will be noted also that the door has an opening 150 which overlies the pumps 90 and 92 so that the operation of these pumps may be observed from outside the cabinet when the door is closed. The door has a latch handle 152 which cooperates with a latch 154 on a wall of the cabinet 36. The plate 70 also carries a plurality of projecting pins 156 positioned at the top and bottom and at other points on the left-hand side of the plate for the supporting of a plastic container and conduit sheet 160. This sheet is shown in FIG. 4 illustrated in greater detail in FIG. 5 where it is shown apart from the supporting panel. A detailed description follows.

The pumps 90 and 92 are relatively standard peristaltic pumps, FIGS. 18-21, having a rotor 170 mounted on a drive shaft 172 and carrying guide wheels 174, which rotate on pins 175 within a housing wall 176, and pressure rollers 178 on pins 179 which exert rolling pressure on a tube lying against the inside of the wall. The pump 92 differs from the normal pump in that one pressure roller at the roller mount 180 is omitted to permit a periodic pressure equalization as will be later described.

Referring now to FIG. 5 and related sectional views in FIGS. 6 to 9, there is shown the plastic container and conduit sheet 160. This container sheet is intended to be disposable to avoid the sterilization problems incident to the use of reusable containers. The sheet is made from a plastic which is preferably transparent, or at least translucent, and heat sealable. Chambers are formed, in the double or folded-over sheet, by heat sealing the peripheries, and plastic tubes are heat sealed into these chambers, FIG. 6, to provide the necessary ingress and egress.

Specifically with reference to FIG. 5, a return chamber 200 is formed in the lower area by a heat sealed periphery 202 with an outlet 202 with an outlet tube 203 sealed at 204, this tube having an arched portion with a top air vent 205. A bottom tube 206 leads to a float valve entry unit 207 within the chamber and to a collapsible sensor pocket 208 (FIG. 17 is cross-section) and thence through a pump tube 209, 209a, 209b to a sealed entrance to one side of a proportioning chamber 210 again formed by a heat sealed periphery. The float valve 207 is designed to close outlet tube 206 when chamber 200 is depleted, FIG. 24. A small orifice 207a permits a bleeding action to relieve negative pressure.

A lower outlet tube 212 leads out of one side of the proportioning chamber 210 in the sheet to a connector 213 which will join to a waste chamber connector 214 on a plastic waste chamber bag 216 lying in compartment 40 (FIGS. 1 and 10). The vented tube 203 from the return chamber also connects at 218 to the waste chamber bag 216. At the top of the proportioning chamber 210 one side of the chamber is connected through a sealed tube 220 to a point near the top of the elevatable pressure relief chamber bag 66 (FIG. 1). A second tube 222 at the top of the proportioning chamber 210 leads through a small pocket chamber 224 (FIG. 7 in cross-section) to a tube 226 which has a bifurcate connector 228 which joins tubes leading to supply containers 58 and 60 (FIG. 1).

The pressure relief chamber 66 also has a connector tube 230 into the bottom which leads to a bifurcate connector 232, the single outlet of which leads to patient tube 234 and body chamber catheter 34. The other branch of the connector 232 leads through a pressure relief pocket 236 (FIG. 9 in section) and then to a tube 238 entering the plastic container sheet 160 to a bacterial trap 240 recessed into the sheet 160 and having a connector tube 242 leading to a pump tube 242a and a connection to a re-entry tube 242b in sheet 160 sealed into the top of return chamber 200.

The proportioning chamber 210 actually consists of two side-by-side chambers which are created by sandwiching a diaphragm or separation wall 250 between the walls 252 and 254 formed from the double sheets. (See FIGS. 8 and 15). This forms two chambers 260 and 270, the chamber 260 on the right, as viewed in FIG. 15, serves to receive return dialysate fluid through tube 209(b) and, under some circumstances, to discharge it to tube 212 and the waste chamber. The chamber 270 on the left, a s viewed in FIG. 15, serves to receive fresh dialysate fluid from tube 222 through pocket 224 and can introduce this fresh fluid into relief chamber 66 through tube 220. These two chambers 260 and 270 have a volumetric effect on each other as will be described. It will be noted that these two chambers 260 and 270 are encased between the rigid dished plates 116 and 120 of the cabinet wall 70 and cover 38 as shown in the sectional view of FIG. 15. Thus, the expansion of one chamber will cause ensmalling of the other and vice versa. There can then be a volumetric proportioning or balancing occur by reason of this arrangement.

The return chamber 200 lies in the compartment formed by the plate 96 and the plate 108 shown in FIG. 14 so that the volume of the chamber 200 can serve as a control by reason of pressure against the movable plate 96 which will influence the micro-switch arm 102. The pocket 208 at the lower right-hand portion of the chamber sheet, supported on bracket 134, as shown in FIG. 17, has a possible influence on the switch arm 136, and the pocket 224 shown in section in FIG. 16 is a collapsible pocket which will reflect a reduction in pressure in the return flow line and thus influence a micro-switch arm 146.

The previously described close-off valves V-1, V-2, V-4 and V-5, which may be referred to as "clamp" valves, are shown in phantom on FIG. 5 to indicate the particular tubes that they are controlling. V-1, for example, controls tube 222; V-2 control tube 220; V-4 controls tube 242; and V-5 controls tube 212.

Referring to FIGS. 10 to 13 the waste bag 216 is formed of a double sheet of plastic with holes 280 and 282 for suspending the bag in the compartment 40, this bag being sealed around its edges as illustrated in FIG. 11. The two top connector tubes are also sealed into the bag at 284. The bag has an outlet neck portion 286 which has a flap assembly 288 containing a malleable metallic stiffener 290. When the bag is to be used, this closure neck can be sealed by folding over the tab portion 290 and bending the ends to a locking position as shown in FIGS. 12 and 13.

Function and Operation

The function of the apparatus above described is to administer dialysate to a patient over long periods of time in a manner to reduce the need for constant supervision by a nurse or technical attendant. The machine must maintain fluid balance, i.e., monitor the amount of fluid administered to the patient to avoid the danger and discomfort of fluid build-up in the peritoneal chamber of the patient; it must also automatically cycle the flow of dialysate and warm the dialysate which will enter the peritoneal chamber. In addition, the machine must be safe and simple to operate and maintain sterility of the system.

It will be recognized that the machine has, first, an electrical cycling unit with a suitable "Power On" switch 292 which controls inflow pump 90 and return pump 92 and the four clamp valves V-1, V-2, V-4, V-5. Other functional elements in the electrical system are a starting switch 294, the micro-switches 104 (FIGS. 4, 14), 138 (FIGS. 4, 17) and 144 (FIGS. 4, 16), and timers T1, T2 and T3. An electronic circuit system system is shown in FIG. 25 illustrating the controlling circuit elements and sequence of operation.

The second basic element of the machine is the replaceable or disposable, flexible, plastic sheet and tube fabrication 160 which can be initially pre-sterilized.

A third basic element of the apparatus is the proportioning reservoir or chamber (FIGS. 4, 15) which consists essentially of the side-by-side chambers 260 and 270 formed by the lamination of the three sheets 250, 252, 254 confined between rigid dished walls 116 and 120. One of the chambers can be filled to the total volume of the rigid housing. If fluid is then subsequently forced into the second chamber, it will force an equal volume out of the first chamber through movement of the intermediate wall 250 which acts as a diaphragm piston. Fluid balance in the patient is achieved by filling one chamber 270 with fresh sterile dialysate prior to the inflow cycle. During inflow, the fluid returned from the previous cycle is pumped into the second compartment 260, thus forcing an equal volume of fresh sterile dialysate into the patient. Thus, the proportioning chamber serves the function of a pump.

In FIGS. 22 and 23, a schematic presentation of the apparatus is illustrated. With reference to these views and the previously described detailed views, to start the cycle, the pressure relief chamber 66 is raised on rod support 64 above the source bottle 58 before the pumps are started. With the clamp valves open, sterile fluid will flow into proportioning chamber 270 through tube 226 until chamber 270 completely fills the rigid chamber 116, 120. The pressure relief chamber is then lowered below the fluid sources 58, 60 to allow fluid to flow to it through valve V-2 and line 220 and then to the line 230 and line 234 which will be connected to the patient. After this catheter line is filled, it is manually clamped. The return pump 92 will pump fluid from the connector 232 to the return chamber 200 where fluid will accumulate until switch arm 102 trips micro-switch 104 to stop the motor of the return pump 92. At this time the fluid supply line 226 is manually clamped. At the same time the inflow pump is automatically turned on and clamp valve V-4 is closed electrically. The inflow pump moves the contents of the return chamber 200 into the waste chamber 216, thereby priming all the lines. The depletion of the liquid in chamber 200 causes pump 90 to create a negative pressure in collapsible pocket 208, thus triggering micro-switch 138 through arm 136 bearing against the pocket to automatically stop inflow pump 90. The float valve 207 closes when liquid leaves the bottom of chamber 200 causing the negative pressure in pocket 208 but an orifices 207a (FIG. 24) permits enough fluid to leak by to allow pocket 208 to return to its normal configuration which will reset switch 138.

At this time the adjustable plate 108 (FIG. 14) can be moved to a position which allows the return chamber to hold a maximum volume equal to the desired exchange volume for a particular patient. This affects the action of plate 96 and micro-switch 104. Now the body catheter 34 can be connected to the patient. The manual clamp is now removed from inflow tube 226 and from the catheter tube 234 and a measured amount of fresh fluid is allowed to run through the lowered pressure relief chamber into the patient. This relief chamber is now moved to its upper position above the fluid source to prevent additional fluid from flowing into the patient.

The machine is now ready for automatic cycling. A suitable start switch 294 on a control unit connected in the electric control circuit is manually actuated to initiate the outflow phase. This opens valve clamps V-1, V-4 and V-5 while V-2 remains closed.

This condition is shown in FIG. 23. The return pump 92 is turned on and two timers T1 and T2 are energized. Timer T1 controls the length of the outflow phase. Timer T2 serves as a check on the outflow from the patient. If the switch 104 sensing hinged plate 96 does not close before timer T2 times out, the first timer T1 is reset and stops until switch 104 closes. This combination prevents the machine from automatically advancing if the return from the patient is less than the desirable rate and indicates a corrective action by the nurse such as catheter manipulation.

When timer T1 times out, the next phase of operation is initiated. Valve clamp V-2 is opened and the return pump 92 is stopped and an optional add cycle is started. The amount of return is observed by the operator. If it is less than desirable, the pressure relief chamber 66 is again lowered and the return pump is manually turned on until the volume in the return chamber is increased to the desired level. The pressure relief chamber is again raised. Once the volume has been determined to be adequate, a start switch 294 (FIG. 25) is closed and the inflow cycle begins.

During the inflow cycle, valve clamps V-1, V-4 and V-5 are closed and V-2 is open. See FIG. 22. Inflow pump 90 is turned on to pump the fluid from the return chamber 200 into the proportioning chamber 260 through tubes 209, 209a, 209b, thus forcing fresh dialysate from charged chamber 270 into the pressure relief chamber 66 from whence it flows into the patient. The pressure relief chamber is constructed of flexible plastic and has a greater volume than that of the rigid housing 116-120 of the proportioning chamber. Also, the inlet 220 to the relief chamber is near the top, while the outlet to tube 230 is at the bottom. If the line to the patient is blocked, fluid will accumulate in the pressure relief chamber exerting a maximum hydrostatic force on the patient determined by its height above the patient.

When the return chamber empties, the switch 138 closes (by closing of float valve and collapsing of pocket 208) and the next phase of the cycle, namely, the equilibration phase, is started. In this phase, valve clamps V-2 and V-4 are closed and V-1 and V-5 are open. Both pumps are off. A timer T3 is energized which controls the length of this phase. Sterile fluid flows from the source 58, 60 into the proportioning chamber 270. This forces the fluid in chamber 260 into the waste chamber 216 through tube 212 and connector 213. Also the heater 118 transmits heat to the fresh dialysate. When timer T3 times out, the unit is automatically switched back to the outflow cycle which has previously been described.

There are several control features in the apparatus not touched upon previously. If, for example, the amount of return fluid exceeds the intended volume as regulated by panels 96 and 108, any excess fluid will flow out of the top of the return chamber through line tube 204 directly into the waste chamber 216. The air vent 205 prevents siphoning once the flow has started.

If switch 144 is triggered by a collapse of flexible pocket 224 (FIG. 16) indicating no hydrostatic head from the supply line 226, the cycle will be interrupted, and, after replenishment, the restart switch must be actuated. The cycle can also be altered by actuating an increase switch 300 (FIG. 25) to replenish fluid when pump 92 is on. Otherwise, the device will continue to cycle: inflow, return, equilibration, inflow return and so on.

In FIG. 25, an electronic control system is illustrated for the purpose of accomplishing the cycling previously described. The electronic control unit has seven control banks or columns A, B, C, D, E, F, and G and an input signal to any particular column or bank cancels the output of any previous column. When a column receives an input, all actions indicated must take place prior to an output signal which may lead to another bank.

Each of these banks controls valves V-1, V-2, V-4 and V-5, pump 92 and pump 90. The circuit also shows the location of a start switch 294 and control switch 104, 138 and 144 as well as timers T1, T2 and T3. A power-on switch is shown at 292 and a starting switch 294 is indicated at three points in the circuit. On the electronic panel, the designation "O" is for "open" along the horizontal lines leading to each controlled valve or pump and the designation "C" means "closed."

Switches which are normally open are shown with parallel lines and switches which are normally closed are shown with parallel lines crossed by an oblique line.

It will be seen that with the power switch 292 on, bank A will carry current to the normally open switch 104 and also turn on return pump 92. When switch 104 is closed by liquid in the return chamber (FIG. 14), current will then flow to bank B closing valve V-4, turning off pump 92, and turning on the inflow pump 90. Fluid will then flow into the waste chamber 216 and ultimately cause the triggering of micro-switch 138 which will pass signal current from bank B to bank C. This will leave valve V-4 on and turn off pump 90. At this point, the circuit is ready for cycling and when the start switch 294 is actuated, the electrical signal will then go to bank D, closing valve V-2 and turning on the return pump 92. Signal current out of bank D will ordinarily pass through the normally closed timer switch T2 and pass to T1; and when timer T1 is phased, current will then flow through a normally closed add switch 296 and through normally closed switch 144 to bank E where all valves are open and the pumps are off. This bank E might function in an "add" cycle.

Current can also pass then through the start switch 294 to bank F where valves V-1, V-4 and V-5 are turned off and inflow pump 90 is turned on. This portion of the cycle will continue until switch 138 is triggered by a depletion of the liquid in the chamber 200 when current will flow around to bank G, thus opening valve V-1 and closing V-2, leaving V-4 closed, and opening V-5 with both pumps being off. This circuit then moves to the timer T3 which is normally open and when this timer is phased, the circuit will recycle by starting again at bank D. The timer T3 is controlling what is called the equilibration phase of the cycle which has been previously described. The electronic circuit in FIG. 25 also shows an add switch 296 which can be actuated manually if fluid is to be added and it also includes an increase switch 300 which can be actuated with pump 92 on to increase the fluid in the circuit.

As will be seen from the above-detailed description, timer T2 which is in the "out" circuit from bank D serves as a check on the outflow from the patient. If the switch 104 does not close before timer T2 times out, the first timer T1 is reset and stops until switch 104 closes.

The maximum negative pressure is controlled during the outflow phase by two devices. Return pump 92 acts as a positive displacement pump during most of its cycle but one roller at roller pin 180 (FIG. 18) is removed so that at a certain point in the rotation, the pump tube 242a is open and unrestricted, thus relieving the negative pressure on the catheter. Secondly, a collapsible chamber 236 in tube 238 (FIG. 9) normally returns to its expanded maximum volume shape if there is no negative pressure within it. The maximum volume of this chamber 236 is greater than the stroke volume of the pump and should the inflow tube 234 be blocked, the pump will collapse chamber 236 during the positive displacement cycle and prevent transmission of any undue negative force to the catheter. The maximum negative force created by the walls of the chamber 236 can readily be calibrated and controlled by the geometrical configuration and the selected material. During the balance of the pump cycle, the open tube 242a will permit retrograde flow and relief of negative pressure and the collapse chamber 236 can return to its normal expanded configuration.

It will be noted that one function of the pressure relief chamber is to prevent flow into the patient if clamp valves V-1 and V-2 should fail since the height of the chamber is above the fluid source 58 and 60. The relation of the tubes 220 and 230 prevent positive pump pressure reaching the patient tube 234 during a regular cycle or when liquid is flowing from the supply bottles. If the patient tube 234 should become blocked, there can be no great build-up of pressure, positive or negative, which would cause discomfort of the patient. If switch 138 should fail, the maximum volume pumped is determined by the maximum volume of the proportioning chamber which is established at a safe level. Also, of course, the adjustment of panel 108 determines maximum volume. The normal volume returned to the patient is equal to the return volume of the previous cycle.