GB1560660A

GB1560660A - Dialyser system and control unit therefor

Info

Publication number: GB1560660A
Application number: GB53726/76A
Authority: GB
Original assignee: Rhone Poulenc Industries SA
Current assignee: Rhone Poulenc Industries SA
Priority date: 1975-12-30
Filing date: 1976-12-23
Publication date: 1980-02-06
Also published as: SE7614700L; ES454667A1; DE2659377C2; CH607927A5; FR2336961A1; JPS6341603B2; FR2336961B1; SE435133B; DE2659377A1; JPS5290191A; NL7614549A; IT1123100B; BE849977A

Description

(54) DIALYSER SYSTEM AND CONTROL UNIT THEREFOR (71) We, RHONE-POULENC INDUSTRIES, a French body corporate of 22 Avenue Montaigne, 75 Paris 8eme, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to a dialyser system for the transfer of solutes and fluids across porous membranes, such as semipermeable membranes, and to a control unit therefor.

The transfer of solutes across porous membranes is known as dialysis. Where the porous membrane holds back dissolved large particles, but not fluid, the process is known as ultrafiltration.

Dialysis and ultrafiltration have important commercial uses in chemical processing to recover and isolate certain constituents.

An important medical usage is in the removal of waste materials and fluids when there has been a failure or impairment of function of the human kidney.

The use of dialysis and ultrafiltration in view of or in supplement to the kidney function involves the use of a dialyser through which blood from the patient is circulated on one side of a semipermeable membrane, with a cleansing fluid, known as the dialysis liquid, circulating on the other side. Since the process involves the transfer of wastes or excess fluid from the blood to the dialysis liquid, it is known as haemodialysis, with the removed fluid being known as the ultrafiltrate.

Haemodialysis can take place only as long as there is a concentration gradient between the waste particles in the blood and those that have been transferred to the dialysis liquid. While it is theoretically possible to provide a continuous supply of fresh dialysis liquid to the dialyser, this would be a wasteful and expensive procedure. In addition, it is desirable for the dialysis system to have a certain degree of portability so that it can be used with great versatility in the home and hospital.

It has previously been proposed to control the amount of ultrafiltrate removed from the patient by arranging that the dialysis liquid flows in a constant volume vessel, and to pump out from this vessel a controlled quantity of liquid which will then be equal to the quantity of liquid passing through the membrane. The apparatus for carrying this method out can be modified by providing suitable valves. With the apparatus operating in this way, in closed circuit, the pressure of the system is measured. The valves are then altered so that dialysis liquid is fed in open circuit from a supply and the system adjusted to produce the pressure noted. In this way the ultrafiltrate flowing through the membrane will continue at the desired rate.

According to the present invention we provide a dialyser system comprising a dialyser having a semi-permeable membrane adapted for dialysis and ultrafiltration, a tank for dialysis liquid, a vent for venting said tank to atmosphere, means for circulating a stream of dialysis liquid between the tank and the dialyser, means for sensing and maintaining a substantially constant level of dialysis liquid in the tank, means for withdrawing at a predetermined rate a fraction of the dialysis liquid from the stream, means for controlling the rate of ultrafiltration taking place in the dialyser in response to the level of dialysis liquid sensed in the tank, and a valve arrangement for enabling the tank to be isolated from the dialyser while the tank is being replenished with fresh dialysis liquid.

Another aspect of the invention provides an ultrafiltration control unit comprising means for connection to a dialyser having a semi-permeable membrane adapted for dialysis and ultrafiltration; a tank for dialysis liquid; means for circulating dialysis liquid between the tank and a dialyser; means for withdrawing at a predetermined rate a relatively small portion of dialysis liquid from dialysis liquid being circulated between the tank and the dialyser; means placing the tank in communication with the atmosphere, sensor means sensing the level of dialysis liquid in the tank, and means for controlling the rate of ultrafiltration taking place in a dialyser connected up to the unit in response to the level of the dialysis liquid in the tank.

In order that the invention will become more fully understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a front view of one embodiment of dialysis and ultrafiltration control unit in accordance with the invention; Figure 2 is a perspective view of a dialysis and ultrafiltration system employing the control unit of Figure 1; Figure 3 is a schematic diagram of the control unit of Figure 1, including illustrative control circuitry; Figure 4 is a view, partially in section, of a control valve used in the control unit of Figure 3; Figure 5 is a view similar to Figure 3 of a second embodiment of the invention; Figure 6 is a view, partially in section. of a control valve used in the control unit shown in Figure 5.

It will be understood that while the invention is being illustrated for haemodialysis and ultrafiltration(i.e. removal of waste products from the blood), it is applicable to any dialysis and ultrafiltration in which substances in solution are separated by a semipermeable membrane of a natural or synthetic origin, such as cellulose. Cellophane, (Registered Trade Mark) parchment, acrylonitrile homopolymer or copolymers, polycarbonate polymers or copolymers through which solutes and colloidal particles may diffuse.

Thus, dialysis can be used in manufacturing processes for the recovery of reagents, catalysts and process chemicals, such as the recovery of sodium hydroxide in the manufacture of viscose.The dialysis and ultrafiltration control unit 10 is used as shown in Figure 1 to regulate the flow of dialysis liquid that originates from a source 30 and is pumped to a dialyser 50 in a manner that achieves precise control of ultrafiltration and the discharge of the waste by a drain line 12.

The dialyser 50 of Figure 2 is a "plate type" of artificial kidney, but other kinds may be used. The particular dialyser 50 of Figure 2 is formed of polypropylene frames 52, 54, 56, with two thin membranes 58 and 60 of porous regenerated cellulose for each blood compartment 62 and 64. Suitable regenerated cellulose membranes for haemodialysis and ultrafiltration are sold and marketed under the Registered Trade Mark "VISKING" by the Union Carbide Company and under the Registered Trade Mark "Cuprophan" by the Enka Glanzstoff Company.

A dialysis liquid compartment 66 is formed within the frames 52, 54 and 56, and the blood compartments 62 and 64. Access to the blood compartments 62 and 64 from the patient being dialysed is via blood ports 68 and 70 and the dialysis liquid pumped from the control unit 10 enters at a port 72 and leaves at a port 74 after flowing in longitudinal grooves 76 of the dialyser frames counter to the flow of the blood.

The regenerated cellulose membranes 58 and 60 in the dialyser 50, which have micropores with mean diameters of the order of about 1 p more or less, keep the blood separated from the dialysis liquid.

Waste products in the blood pass through the membranes 58 and 60 by virtue of a concentration gradient. When the dialysis liquid is first circulated, it is free of waste products. Consequently those waste products having a mean diameter less than that of the pores in the membranes 58 and 60 will pass through from the blood into the dialvsis liquid. This process continues until the concentration difference of the waste materials on both sides of the membrane approaches zero, whereupon the dialysis liquid needs to be replaced by a fresh uncontaminated supply.

In addition, where the pressure on the blood side is sufficiently greater than the pressure on the dialysis liquid side, i.e.

sufficient to compensate for the inherent osmotic pressure, fluid will pass through membranes 58 and 60 from the blood into the dialysis liquid. This process is known as ultrafiltration.

The dialysis and ultrafiltration control unit 10 provides a convenient way of replacing the waste dialysis liquid with a fresh supply while minimising interruption of the dialysis process. In addition the removal of waste water by ultrafiltration is controlled with precision.

A patient in need of dialysis, is connected to the dialyser by inflow and outflow lines 80 and 82, which are connected to the patient for example in the arm 84, by cannulae 86 and 88, inserted into an artery and a vein respectively.

The dialyser 50 shown in Figure 2 is of a low resistance type, so that the patient's blood pressure is generally sufficient to maintain a suitable flow of blood into and through the dialyser 50, at a rate which is generally from 150 to 200 millilitres per minute. When it is desired to increase the rate to the order of about 300 millilitres per minute, a blood pump 90 of any conventional type is employed. The peristaltic pump illustrated has rotatable rollers 92 and 94 that squeeze tube 80 by squeezing it against an annular wall, and force the blood into the dialyser.

Upstream of the blood pump 90, on the arterial side, there is a container 96 of priming solution, usually comprising a conventional saline solution containing a small amount of heparin sodium. This is used to fill the line before it is attached to the patient at 84 via 86 and 88. During dialysis the container 96 is closed off by a clamp 98 and a clamp 100 is open. At the end of dialysis, the blood in the line between the patient and the dialyser is rediffused into the patient by closing clamp 100 and opening the clamp 98 to allow the saline and the heparin solution to force the blood in the line back into the patient.

On the venous side of the system there is a bubble catcher 102 communicating with a syringe 104 and a blood pressure indicator 106. When a clamp 108 on the venous side is opened, the syringe 104 can be used to control the level of blood in the bubble catcher 102 and to remove air. The blood pressure is monitored by the indicator 106 which is connected by a lead (not shown) to a sensor cable 110 of the control unit 10.

Once the dialyser 50 is connected to the patient, the control unit 10 is connected to the dialyser by lines 112 and 114, connected to an outlet port 120 and an inlet port 122, respectively, to enable pumping of the dialysis liquid to and from the dialyser.

Waste fluid extracted from the blood by ultrafiltration and carried by the returning dialysis liquid is discharged through a drain line 12 from a drain port 124.

The dialysis liquid is supplied to the control unit 10 at an input port 116 via a line 118 from the source 30. It will be understood that the flow and distribution of dialysis liquid within the control unit 10 are through and via various lines and tanks, etc., as and in the manner shown schematically in the flow sheet of Figure 3 described more fully hereinafter.

The rate of ultrafiltration is controlled by the setting of a dial 126.

The conditions of various monitors associated with the dialysis are indicated on the unit 10 by warning lights 128, 130, 132, 134 and 136. Thus, any abnormal blood pressure condition is detected by a sensor that responds to the indicator 106 and is connected to the warning light 128. There is also a monitoring of dialysis liquid temperature by a thermostatic probe 138 at the output of the dialysis liquid source 30 and a corresponding warning light 130. Another probe 140 at the output of the dialysis liquid source 30 measures the electrical conductivity of the dialysis liquid and indicates any abnormal measurement at a corresponding third warning light 132.

If all monitored conditions are satisfactory this is indicated by the "NORM" light 134; otherwise there is a warning indication by the "ABNORMAL" light 136. In addition, upon occurrence of an abnormal condition, a reset indicator and switch 142 is activated. The unit 10 can then be reset by depressing the switch 142.

Other monitors may also be provided, for example, to measure dialysis liquid flow e.g.

by a variable-area flow tube; dialysis liquid pressure by a manometer or other pressure gauge; and blood leaks into the dialysis liquid effluent or line 114 by a photoelectric pick-up to detect colour change.

The components that provide precision control over dialysis and ultrafiltration by the unit 10 are shown schematically in Figure 3.

Dialysis liquid from the source 30 (Figure 2) enters at port 116 and passes via line 150 (Figure 3) to a holding tank 152. Filling takes place until there is overflow on a drain line 154, with the overflow exiting at the drain port 124. Filling can take place by pumping from the source 30, but it is generally satisfactory to use gravity flow by having the source 30 above the unit 10 and a suitable clamp (not shown) on the external fill line 118 (Figure 2).

This overflow fill technique ensures that a sufficient amount of dialysis liquid is in the holding tank 152. Once the holding tank 152 is filled, its contents may be readily pumped to a bath tank 156 by a generally occlusive pump 158, a supply line 160 and a fill line 164.

Once there is dialysis liquid in the bath tank 156, it can be circulated to and from the dialyser 50 (Figure 2) via ports 120 and 122 by pumps 166 and 168. Outflow takes place via line 170, pump 166, line 172 and port 120 to the dialyser 50.

The dialysis liquid returns from the artificial kidney via port 122, a line 174, pump 168, line 176 and into the bath tank 156, thus completing the cycle.

The foregoing flow can take place only if a valve 180 located between the bath tank 156 and the pumps 166 and 168 leaves lines 170 and 176 open. When the bath tank 156 is being filled, the valve 180 is quickly closed so that no flow can take place between the bath tank 156 and the dialyser 50. However, any prior flow of dialysis liquid to the dialyser continues to take place via a by-pass line 182.

When ultrafiltration is to take place, or the bath tank 156 is to be emptied, a pump 190 is operated to drain liquid from the tank 156 via line 192 and expel it via line 194 into the drain line 196, port 124 and drain line 12.

Details of a suitable valve 180 are shown in Figure 4. The valve mechanism includes a frame 200 on which are mounted guide bars 202 and 204 for a pressure plate 206. The plate 206 has bearing apertures (not shown) to permit it to slide along the guide bars 202 and 204, and is attached to a nut 208 which is engaged by an endless screw 210, forming an extension of the armature shaft 212 of a drive motor 214.

When the motor 214 is actuated from a controller panel 220 described below, the plate 206 is quickly driven up or down until a limit switch 216 or 218 is contacted to turn off the motor. When the plate 206 is in its down position as shown, the by-pass line 182 is closed and the dialyser supply lines 170 and 176 are open. Conversely, when the plate 206 is in its up position, the by-pass line 182 is open and the lines 170 and 176 are closed.

The various valves and pumps may be actuated and controlled in any desired manner. A particularly desirable arrangement, however, is as follows: The necessary operations are controlled by suitable circuitry mounted on a controller panel 220 and by a level sensor 222, on a vent tube 224 of the bath tank 156. A similar level sensor 226 on a vent tube 228 can be used with the holding tank 152. Voltage at the desired level is supplied from the cable 230 by a transformer 232. After the dialysis liquid has filled the holding tank 152, the FILL switch 231 for the bath tank 156 is closed. This sets a flip-flop 234 which produces a high level voltage on a primary output lead until the flip-flop is reset and operates pump 190 which drains the bath tank 156 until a sensor 236 associated with the pump 190 detects the absence of any further flow and applies a signal to the reset terminal R of the flip-flop 234.

For initial operation, the bath tank 156 will be empty, so that the sensor 236 operates immediately to terminate the operation of the pump 190.

A second flip-flop 240 simultaneously responds to the closure of the fill switch 231 to operate the valve 180, closing the lines 170 and 176, and opening the by-pass line 182. This has no effect on the initial operation, but subsequently when the bath tank 156 is drained, this permits continued flow of the dialysis liquid in a separate loop to and from the dialyser 50 until the tank 156 is full.

After a suitable delay period to permit full drainage of the bath tank 156, a single trip multivibrator 250 operates for a constant time interval to operate the pump 158 and pump fresh dialysis liquid from the holding tank 152 into the bath tank 156. The single trip multivibrator is of standard design with a built-in delay line at its set terminal S. At the end of the delay interval the multivibrator 250 operates for a re- scribed discharge interval determined in standard fashion by a resistance-capacitance network.

Once the tank 156 is full, which may be indicated by the level sensor 222, the liquid may then be circulated to the dialyser by operating the dialyse switch 260. This resets the flip-flop 240 to reverse the operation of the valve 180, and thus open lines 170 and 176 and close by-pass line 182.

The closure of the switch 260 also applies a constant bias voltage from the power supply 262 to the pump 166, while the pump 168 is supplied with a voltage from an amplifier 264 according to the level sensed by the sensor 222. While the bath tank 156 is being drained, the sensor voltage 222 is prevented from affecting the amplifier 264 by a gate G which is cntrolled from the complementary output Q of the flip-flop 240. As a result, the amplifier 264 operates the pump 168 at a maintenance level to ensure circulation of dialysis liquid in the separate loop formed by the by-pass line 182 and the connections to the dialyser. To ensure that the pump 166 (which is inactive during the filling of the bath tank 156), will not interfere with the maintenance flow, it is desirable for the pump 166 to have an internal by-pass which is closed when the regular constant voltage bias is applied during regular dialysis.

The dialyse switch 260 also operates the ultrafiltration control amplifier 270 which applies an appropriate voltage to the occlusive drain pump 190 in accordance with the desired rate of ultrafiltration set by the control knob 126 (Figure 1).

When the ultrafiltration rate is set for zero, no waste liquid is withdrawn from the patient and the feedback amplifier 264 adjusts the speed of the pump 168 so that the pressure of the dialysis liquid in the dialyser is substantially the same as the blood pressure. Consequently no waste fluid from the blood can flow through the membrane.

As the ultrafiltration rate is set above zero on the control knob 126, the pump 190 operates and the level of fluid in the tank 156 drops, so that sensor 222 causes an increase in the voltage applied to the amplifier 264, to increase the speed of pump 168 relative to the constant speed of the pump 166. The result is a reduction in the pressure of dialysis liquid in the dialyser, that is to say an augmentation of the transmembrane pressure, so that waste liquid passes from the patient's blood into the dialysis liquid.

Thus the volume of the liquid in the dialysis liquid circuit is increasing and the level of liquid in the tank 156 rises. Thus, dialysis liquid is withdrawn at a controlled rate in the drain via port 124.

The rate of ultrafiltration established by the control knob 126 can be changed by increasing the drainage rate. A separate discharge port (not shown) can be provided for the ultrafiltrate together with auxiliary pump and monitoring circuitry. If desired, the same pump 190 can be employed for both purposes.

By contrast with the prior art, the use of the two pumps 166 and 168 to feed the dialyser, in conjunction with the sensing of the level in the bath tank 156 by the sensor 222, permits precision control over ultrafiltration. The system is self-adjusting, regardless of conditions such as change in blood pressure or pressure drop in the fluid circuits.

In addition, the provision of the valve 180 with bypass line 182 permits the dialysis to be maintained while the bath tank 156 is being supplied with fresh dialysis liquid, thereby minimising interruptions to the dialysis treatment of the patient.

It will be understood that the circuitry of the controller panel has been expressly simplified for purposes of explanation and that the various operations described above can be performed in a wide variety of ways.

The controller panel 220 also includes illustrative circuitry for the indicators 128.

130, 132, 134 and 136(Figure 1). As noted above the sensors supply signals to the panel 220 over a cable 110. The individual lines in the cable 110 are connected to respective indicators 128, 130 and 132. In addition, lines are included that go to an OR gate 280 so that if any abnormal condition is indicated there will also be an input to the indicator 136; otherwise, because of the NOT gate 282 the indicator 134 will be illuminated to show that conditions are "normal".

The OR gate 280 and the NOT gate 282, which can be an ordinary inverting amplifier, are standard electronic components, along with the flip-flops 234 and 240, and the delay one-shot multivibrators 250.

Moreover, instead of discrete components.

the controller panel 220 may employ integrated circuit chips to consolidate as many electronic functions as desired on one chip.

Suitable pump units 166 and 168 are provided by Model 08-33-103 gear pumps manufactured by the Micromite Company of California. The motor portion operates at a speed determined by the voltage input and has a magnetic drive for the pump portion.

The pump 166 may be provided with a suitable by-pass. The voltage supplied to the pump 168 may be regulated in accordance with the load to maintain constant speed, or the motor portion may be of the synchronous type to ensure constant speed regardless of load.

The pump 158 may be a centrifugal pump, while the pump 190 is occlusive, i.e., of the positive drive type for example as provided by a piston pump. The motor 214 for the valve 180 may be of the ordinary gear type.

Level sensor 222 may be. a linear voltage differential transformer with a movable core mounted on a float responsive to the level of the liquid in the vent 224 to control the coupling to the transformer.

Other suitable kinds of sensors may be employed, such as optical, capacitive or a float provided with various integrated circuitry for bringing about a linear voltage response.

The system is not completely closed, access to the atmosphere being provided via the vent tubes 224 and/or 228 (Figure 3), so that bubbles of gas, such as air, that otherwise might enter and remain in the dialysis liquid and disrupt the efficient functioning of the dialyser 50 are readily eliminated from the system.

A second embodiment of the invention is illustrated in Figures 5 and 6. This embodiment is generally similar in overall function and mode of operation to that of Figures 1 to 4, and like reference numerals will be employed for elements having like functions.

In this second embodiment of the invention precision control over the operation of the dialyser and particularly the removal of waste water by ultrafiltration, is achieved by the automatic switching back and forth between two storage tanks for the dialysis liquid in conjunction with two pumps in the respective paths to and from the dialyser.

These two pumps operate at complementary speeds so that as the speed of one is increased, the speed of the other is decreased, thus maintaining constant flow through the artificial kidney. A prescribed rate of ultrafiltration is maintained by a third pump under the control of level sensors associated with the tanks.

Two tanks for dialysis liquid are provided but in this instance instead of one tank being a 'holding" tank for the other as in the first embodiment, the two tanks are so arranged that they can be automatically switched in and out of circuit, thereby making it possible to carry out the dialysis on the patient with a minimum of interruption.

Dialysis liquid from the source 30 enters at the port 116 and is carried by gravity through a line 300 to a valve 302 and also by a line 304 to a valve 306. When the valve 302 is opened, dialysis liquid enters a tank 308 through line 310. Similarly, when the valve 306 is opened, dialysis liquid enters a tank 312 through line 314.

Once the tanks 308 and 312 are filled, dialysis liquid can be pumped from either, according to the setting of a valve 320.

Assuming that the valve 320 is set according to Figure 6, dialysis liquid can flow from tank 312 via line 322, to the pump 324 and along the line 326 to the dialyser port 120.

The liquid returns from the dialyser via the port 122, line 328, the pump 330 and line 332 to the tank 312.

When the system is ready for a fresh supply of dialysis liquid, the valve 320 closes with respect to tank 312 and opens with respect to tank 308, so that liquid is drawn along a line 334, to a junction with line 322, to the pump 324. The pump 324 feeds the liquid along the line 326 to port 120. The liquid returns on the line 328 into the pump 330, along line 332 to a junction with line 336 that, like line 334, passes through the valve 320 back to the tank 308.

While fresh dialysis liquid is being drawn from the tank 308, the spent dialysis liquid in tank 312 is drawn along a line 338 through a valve 340 and expelled by gravity into a drain line 342 and drain 344. Similarly, while fresh dialysis liquid is being drawn from tank 312, the spent dialysis liquid in tank 308 is drawn along a line 346 through a valve 348 and expellled by gravity into a drain line 350 and drain 344.

When ultrafiltration is to take place, a pump 352 is operated to draw returning dialysis liquid from the return side of the pump 330 via a junction 354 in the line 332 between the pump 330 and the valve 320.

From the junction 354 the liquid is drawn through a line 356, pump 352 and expelled via line 358 and exit port 360. In order to avoid ultrafiltration taking place simultaneously with tank drainage, separate drain ports 344 and 360 are provided. The ultrafiltrate from the exit ort 360 can be measured to confirm the proper operation of the ultrafiltration controller.

The foregoing operations are controlled by circuitry mounted on a controller panel 400 and by level sensors 402 and 404 mounted on vent tubes 406 and 408 of the tanks 308 and 312, respectively. As before, the vent tubes 406 and 408 are open to the atmosphere.

Details of a suitable valve 320 are shown in Figure 6. The valve mechanism includes a frame 420 with pressure plates 422 and 424 that are able to engage the lines 322 and 332, and the lines 334 and 336. The pressure plates are driven by a drive plate 426 through coil springs 428, 430, 432 and 434.

The drive plate 426 is guided by rollers 436 and 438 and is threadedly engaged by a shaft 440, which is an extension of the armature shaft 442 of a drive motor 444.

When the motor 444 is operated from the controller panel 400 (by the "V" lines), the plate 426 is quickly driven up or down until a limit switch 446 or 448 is contacted to turn-off the motor 444, when the plate 426 is in the position shown in Figure 6, the lines 334 and 336 are closed by the pressure transmitted to the plate 424 through the springs 432 and 434, the lines 322 and 332 are open, and a signal is available from the limit switch 446. Conversely, when the plate 426 is drawn upwardly by the threaded shaft 440 until the plate 422 contacts the upper limit switch 448, it closes the lines 322 and 332 and opens the lines 334 and 336.

The motor 444 is advantageously of the model 12F "pancake" type available from the Printed Motors Division of Kollmorgen Corp. of Glen Cove, New York.

Voltage at the desired level for this second embodiment is supplied from the cable 230 by a transformer 232.

The unit 10 is set into operation with the liquid source 30 connected at the port 116, by closure of the switch 460. This sets a flip-flop 462 which opens the valve 302 until an appropriate level is detected by the level sensor 402, which resets the flip-flop 462 and shuts the valve 302. A flip-flop is a two state electronic device with one output at a high level or a low level in accordance with the signal at a set terminal S and a reset terminal R.

Once the tank 308 is full, it can be used for dialysis by the pumps 324 and 330, provided that the lines 334 and 336 are open (i.e. the limit switch 448 of the valve 320 is on and the lines 322 and 332 are closed (Figure 6). With the limit switch 448 on and tank 308 full (so that a control signal from the level sensor 402 appears), an AND gate 463 is operated. This operates a gate 464 to permit the level of the signal from the sensor 402 to control the pump amplifiers 466 and 468, to start the dialysis flow from tank 308.

While the first tank 308 is connected into the dialysis liquid circuit, the second tank 312 is filling, as controlled by the Q output of the flip-flop 470 operated by the AND gate. The delay unit 472 to permit closure of a NOT gate 474 if no operation of the valve 320 to change the limit switch responses is indicated.

The Q output of the flip-flop 470 also opens the drain valve 348 for a timed interval through a one-shot multivibrator 476, as well as the valve 320 after a delay interval provided by a delay unit 478. This changes the setting of the valve 320 to transfer quickly dialysis to the second tank 312 when it is filled to the appropriate level indicated by the sensor 404, which acts with the signal from the first limit switch 446 at an AND gate 480 to operate the gate 482 for control of the pump amplifiers 466 and 468.

In the meantime the Q output of the flip-flop 470 fills the first tank 308 and opens the valve 340 by a one-shot multivibrator 482 through a delay unit 484.

As a result, the control unit 10 automatically switches the tanks 308 and 312 between dialysis and fill cycles. Appropriate time delay periods can be provided as desired.

In addition, the control unit 10 provides precision control over ultrafiltration. The ultrafiltrate is drawn by the occlusive pump 352 which is operated by a variable amplifier 486, the setting of which is determined by the control knob 126.

When the ultrafiltration rate is set for zero, no waste fluid is to be drawn from the artificial kidney 50 and the amplifiers 466 and 468 adjust the speeds of the pumps 324 and 330 so that the pressure of the dialysis liquid in the artificial kidney is substantially the same as that of the blood. Consequently no waste fluid from the blood can flow into the dialysis liquid.

As the ultrafiltration rate is set above zero, the pump 352 operates the level of fluid in the sensor 402 or 404 (depending on which tank is dialysing at the moment) drops, causing an increase in the voltage of the amplifier 468 and a corresponding decrease in the voltage of the amplifier 466. In effect, the amplifiers 466 and 468 act as an operational amplifier with cross-coupled input I and negative input NI terminal. A constant amplitude reference voltage is provided by the power supply 488.

As a result, any increase in speed of the pump 330 is matched by a decrease in the speed of the pump 324. Conversely, any decrease in the speed of the pump 330 is matched by an increase in the speed of the pump 324. Consequently, the dialysis liquid flow rate is maintained appreciably constant despite any change in the rate of ultrafiltration. In the case of the plate-type artificial kidney of Figure 2, the pumps 330 and 324 provide negative pressure in the artificial kidney, with the pump 330 operating faster than the pump 324.

The rate of ultrafiltration established by the control knob 126 can be checked by measuring the drainage rate.

The use of the two pumps 324 and 330 to feed the dialyser 50, in conjunction with the sensing of the level in the dialysing tank 308 or the tank 312 by the sensor 402 or 404 (respectively) permits precision control over ultrafiltration. The system is self-adjusting, regardless of ambient conditions, to the desired operation.

It will be understood that the circuitry of the controller panel 400 has been expressly simplified for purposes of explanation and that the various operations described above can be performed in a wide variety of ways.

The controller panel 400 also includes illustrative circuitry for the indicators 128, 130, 132 and 136 (Figure 1). The sensors supply signals to the controller panel 400 over a cable 110. The individual lines in the cable are connected to respective indicators 128, 130 and 132. In addition, the lines go to an OR gate 490 so that if any abnormal condition is indicated there will also be an input to the indicator 136; otherwise, because of the NOT gate 464 the indicator 134 will be illuminated to show that conditions are "normal".

The various components can be of the same type as described with reference to Figure 3.

WHAT WE CLAIM IS: 1. A dialyser system comprising a dialyser having a semi-permeable membrane adapted for dialysis and ultrafiltration, a tank for dialysis liquid, a vent for venting said tank to atmosphere, means for circulating a stream of dialysis liquid between the tank and the dialyser, means for sensing and maintaining a substantially constant level of dialysis liquid in the tank, means for withdrawing at a predetermined rate a fraction of the dialysis liquid from the stream, means for controlling the rate of ultrafiltration taking place in the dialyser in response to the level of dialysis liquid sensed in the tank, and a valve arrangement for enabling the tank to be isolated from the dialyser while the tank is being replenished with fresh dialysis liquid.

2. A dialysis system according to claim 1, wherein valve means provide a by-pass for dialysis liquid in the dialyser system, while said tank is isolated therefrom, as it is being replenished with fresh dialysis liquid.

3. A dialyser system according to claim 1, wherein two tanks for dialysis liquid are provided, and valve means connect each tank to the dialyser and disconnect the other tank from the dialyser and vice versa.

4. A dialyser system according to claim 3, wherein further valves connect each tank in turn to a source of fresh dialysis liquid, and connect that tank to a drain, while the valve means place the other tank in com

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. delay unit 472 to permit closure of a NOT gate 474 if no operation of the valve 320 to change the limit switch responses is indicated. The Q output of the flip-flop 470 also opens the drain valve 348 for a timed interval through a one-shot multivibrator 476, as well as the valve 320 after a delay interval provided by a delay unit 478. This changes the setting of the valve 320 to transfer quickly dialysis to the second tank 312 when it is filled to the appropriate level indicated by the sensor 404, which acts with the signal from the first limit switch 446 at an AND gate 480 to operate the gate 482 for control of the pump amplifiers 466 and 468. In the meantime the Q output of the flip-flop 470 fills the first tank 308 and opens the valve 340 by a one-shot multivibrator 482 through a delay unit 484. As a result, the control unit 10 automatically switches the tanks 308 and 312 between dialysis and fill cycles. Appropriate time delay periods can be provided as desired. In addition, the control unit 10 provides precision control over ultrafiltration. The ultrafiltrate is drawn by the occlusive pump 352 which is operated by a variable amplifier 486, the setting of which is determined by the control knob 126. When the ultrafiltration rate is set for zero, no waste fluid is to be drawn from the artificial kidney 50 and the amplifiers 466 and 468 adjust the speeds of the pumps 324 and 330 so that the pressure of the dialysis liquid in the artificial kidney is substantially the same as that of the blood. Consequently no waste fluid from the blood can flow into the dialysis liquid. As the ultrafiltration rate is set above zero, the pump 352 operates the level of fluid in the sensor 402 or 404 (depending on which tank is dialysing at the moment) drops, causing an increase in the voltage of the amplifier 468 and a corresponding decrease in the voltage of the amplifier 466. In effect, the amplifiers 466 and 468 act as an operational amplifier with cross-coupled input I and negative input NI terminal. A constant amplitude reference voltage is provided by the power supply 488. As a result, any increase in speed of the pump 330 is matched by a decrease in the speed of the pump 324. Conversely, any decrease in the speed of the pump 330 is matched by an increase in the speed of the pump 324. Consequently, the dialysis liquid flow rate is maintained appreciably constant despite any change in the rate of ultrafiltration. In the case of the plate-type artificial kidney of Figure 2, the pumps 330 and 324 provide negative pressure in the artificial kidney, with the pump 330 operating faster than the pump 324. The rate of ultrafiltration established by the control knob 126 can be checked by measuring the drainage rate. The use of the two pumps 324 and 330 to feed the dialyser 50, in conjunction with the sensing of the level in the dialysing tank 308 or the tank 312 by the sensor 402 or 404 (respectively) permits precision control over ultrafiltration. The system is self-adjusting, regardless of ambient conditions, to the desired operation. It will be understood that the circuitry of the controller panel 400 has been expressly simplified for purposes of explanation and that the various operations described above can be performed in a wide variety of ways. The controller panel 400 also includes illustrative circuitry for the indicators 128, 130, 132 and 136 (Figure 1). The sensors supply signals to the controller panel 400 over a cable 110. The individual lines in the cable are connected to respective indicators 128, 130 and 132. In addition, the lines go to an OR gate 490 so that if any abnormal condition is indicated there will also be an input to the indicator 136; otherwise, because of the NOT gate 464 the indicator 134 will be illuminated to show that conditions are "normal". The various components can be of the same type as described with reference to Figure 3. WHAT WE CLAIM IS:

1. A dialyser system comprising a dialyser having a semi-permeable membrane adapted for dialysis and ultrafiltration, a tank for dialysis liquid, a vent for venting said tank to atmosphere, means for circulating a stream of dialysis liquid between the tank and the dialyser, means for sensing and maintaining a substantially constant level of dialysis liquid in the tank, means for withdrawing at a predetermined rate a fraction of the dialysis liquid from the stream, means for controlling the rate of ultrafiltration taking place in the dialyser in response to the level of dialysis liquid sensed in the tank, and a valve arrangement for enabling the tank to be isolated from the dialyser while the tank is being replenished with fresh dialysis liquid.

munication with the dialyser.

5. A dialyser system according to any preceding claim, wherein the means for circulating the stream of dialysis liquid includes two positive flow pumps, one disposed upstream, the other downstream of the dialyser and the means for controlling the rate of ultrafiltration comprises means for controlling the operation of the two pumps in relation to each other in response to the level of dialysis liquid sensed in the tank, in such a manner as to maintain a substantially constant level of dialysis liquid in said tank.

6. A dialyser system according to claim 5, wherein one of the two positive flow pumps is driven by a constant speed motor and the other is driven by a variable speed motor.

7. A dialyser system according to claim 6, wherein the pump driven by the constant speed motor is disposed upstream of the dialyser and the other pump is disposed downstream of the dialyser, and means are provided for increasing the speed of the variable speed motor when the level of dialysis liquid in the tank decreases and vice versa.

8. A dialyser system according to claim 6, wherein the pump driven by the constant speed motor is disposed downstream of the dialyser and the other pump is disposed upsteam of the dialyser, and means are provided for decreasing the speed of the variable speed motor when the level of the dialysis liquid in the tank increases and vice versa.

9. A dialyser system according to claim 5, wherein the two pumps are driven at complementary speeds, one increasing when the other is decreasing and vice versa.

10. An ultrafiltration control unit comprising means for connection to a dialyser having a semipermeable membrane adapted for dialysis and ultrafiltration; a tank for dialysis liquid; means for circulating dialysis liquid between the tank and a dialyser; means for withdrawing at a predetermined rate a relatively small portion of dialysis liquid from dialysis liquid being circulated between the tank and the dialyser; means placing the tank in communication with the atmosphere, sensor means for sensing the level of dialysis liquid in the tank, and means for controlling the rate of ultrafiltration taking place in a dialyser connected up to the unit in response to the level of the dialysis liquid in the tank.

11. An ultrafiltration control unit as claimed in claim 10, wherein the means placing the tank in communication with the atmosphere is a vent tube leading from the tank, and wherein the means for maintaining a substantially constant level of dialysis liquid in the tank comprises a level sensor for sensing the level of dialysis liquid in the vent tube.

12. An ultrafiltration control unit as claimed in claim 10 or 11, wherein the means for circulating dialysis liquid includes two positive-flow pumps, one for connection upstream and the other for connection downstream of a dialyser, the means for controlling the rate of ultrafiltration across the semipermeable membrane of a dialyser comprising means for controlling the operation of the two pumps in relation to each other in response to the level of dialysis liquid sensed in the tank in such a manner as to obtain a dialysis liquid pressure in the dialysate compartment of the dialyser which leads to a rate of ultrafiltration taking place across the semipermeable membrane which is substantially the same as the rate of withdrawal of dialysis liquid.

13. An ultrafiltration control unit as defined in claim 12, wherein the means for controlling the operation of the two pumps in relation to each other is arranged for driving at least one of the pumps at a speed dependent on an output signal indicating the level of dialysis liquid in the tank.

14. A dialyser system substantially as hereinbefore described, with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

15. A dialyser system substantially as hereinbefore described, with reference to and as illustrated in Figures 1, 2, 5 and 6 of the accompanying drawings.

16. An ultrafiltration control unit for a dialyser, such control unit being constructed and arranged to operate substantially as herein described, with reference to, and as illustrated in, Figures 1 to 4 or Figures 1, 2, 5 and 6 of the accompanying drawings.