US3508656A - Portable dialysate supply system - Google Patents

Description

April 28, 1970 E. J. SERFASS ET AL 3,508,656

PORTABLE DIALYSATE SUPPLY SYSTEM 2 Sheets-Sheet Filed April 10, 1968 mohhzoi m I k (\1 United States Patent 3,508,656 PORTABLE DIALYSATE SUPPLY SYSTEM Earl J. Serfass, St. Petersburg, and Vernon H. Troutner, Clearwater, Fla., assignors to Milton Roy Company, St. Petersburg, Fla, a corporation of Pennsylvania Filed Apr. 10, 1968, Ser. No. 720,104 Int. Cl. B01d 35/14, 35/00 US. Cl. 210-90 4 Claims ABSTRACT OF THE DISCLOSURE A portable blood dialysis system in which dialysate fluid is mixed and supplied with a constant concentration is described. Water and dialysate fluid concentrate are mixed to form dialysate fluid which is supplied to the dialyzer. The concentration of the dialysate fluid is continuously monitored by a conductivity cell. The output of the conductivity cell is applied to control a pump which supplies the concentrate. This pump also has a secondary speed control loop. A tachometer in the secondary loop corrects speed variations caused by changes other than the conductivity cell output signal.

BACKGROUND OF THE INVENTION One of the most successful means for treating chronic kidney failure is by hemodialysis using an artificial kidney system. In hemodialysis the patients blood is circulated from an artery through an artificial kidney, or dialyzer, where excess water and waste materials are removed. The blood is returned to the patients veins.

A central station dialysate supply system for supplying dialysate fluid to a number of patients in a hospital is described in Transactions of the American Society of Artificial Organs, vol. X, 1964, page 107, Grimsrud, Cole, Lehman, Babb and Scribner.

Also, in the Austin et al. Patent 3,352,779 there is described a system for mixing dialysate fluid in large batches for supply to a number of patients.

Since the patient must undergo dialysis treatment several times a week it is desirable that a system be provided which can be used by the patient in his home. A single patient dialysate supply system with extensive monitoring controls which makes the system safe for use by the patient himself is described in Controlled Blood Dialysis System, Ser. No. 563,523, now US. Patent No. 3,441,136, filed July 7, 1966, Earl J. Serfass, John E. Martin and William E. Wilson, Jr. Such a single patient system is also described in a paper presented before the Instrument Society of America, 22nd Annual ISA Conference and Exhibit, Sept. 11-l4, 1967, by Dr. E. J. Serfass, Preprint Publication No. 26-1-BIOMED67.

These single patient systems have found widespread successful use. However, they do not meet all requirements of some patients because the systems utilize expensive proportioning apparatus for mixing dialysate fluid and because the systems are quite large and not portable.

All of the blood dialysis supply systems described above use a two-stroke pump to mix dialysate concentrate with water to produce a supply of dialysate fluid. These pumps have very accurate controlled strokes so that the water and the concentrate are mixed in precise Volumetric proportions. The pumps are relatively expensive and bulky. Further, extensive movement of the pump will affect the calibration so they are not suitable for a truly portable system.

While these two-stroke pumps do mix concentrate and water in precise volumetric proportions, the resulting dialysate fluid does not necessarily have a controlled concentration. When the density of the concentrate changes with temperature, the concentration of the dialysate fluid changes. What is required in dialysate supply systems is the production of a dialysate fluid having controlled sodium and chloride concentration at a prescribed temperature.

The variation of the concentration of the dialysate fluid with change in temperature is a particular problem in a system having extensive monitor controls such as the systems described in the above-mentioned Serfass reference and Serfass et al. patent application. These systems have a concentration monitor which sounds an alarm when the concentration of the dialysate fluid varies outside of preset limits. When dialysis treatment is performed during the night, as it is frequently, the patient will often be awakened by the alarm when the concentration of the dialysate fluid changes because of a change in the ambient temperature of the top water.

SUMMARY OF THE INVENTION This invention relates to blood dialysis supply systems and more particularly to a portable blood dialysis system.

In accordance with an important aspect of this invention, the dialysate fluid and tap water are mixed in a system which includes a servo controlled pump. The servo controlled pump supplies concentrate to a mixer. The water and concentrate are mixed to form dialysate fluid having a controlled concentration. A conductivity cell monitors the concentration of the dialysate fluid and the resultant signal controls the pump. This permits the use of a relatively simple, compact, inexpensive pump in the system rather than more costly and bulky volumetric measuring devices.

Further in accordance with this invention, a secondary control loop is provided for the pump by a tachometer control. When the speed of the pump varies because of variations other than conductivity, line voltage, for example, the tachometer senses these changes in the pump speed and quickly restores the pump to its normal operating speed.

Accordingly, it is an important object of the present invention to provide a simple, easily maintained, inexpensive dialysate supply system.

It is another object of the present invention to provide a portable dialysate supply system which can be operated from a volt, 15 ampere power supply and an ordinary cold water supply.

The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and appended claims together with the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a diagram of the portable dialysate supply system; and

FIG. 2 shows a schematic diagram of the control loops for the concentrate pump.

DESCRIPTION OF A PARTICULAR EMBODIMENT Referring now to FIG. 1, the block diagram shows the circulation of dialysate fluid and the electrical control functions performed by the system. In FIG. 1 the hydraulic conections are shown with heavy lines while the electrical connections are shown with lighter lines.

The dialysate fluid to be circulated in the dialyzer is a mixture of tap Water from the source 34 and concentrate from the concentrate reservoir 15. The composition of the dialysate fluid may be changed in accordance with the therapy required for a particular patient. In general, the composition of the dialysate fluid is described in Hemodialysis for Chronic Renal Failure, Freeman, M'aher and Schreiner, Annals of Internal Medicine, volume 62, No. 3, March 1965. The concentrate and tap water are mixed in the proper proportions in the mixer 11. Water from the source 34 passes through the pressure reducing valve 2 to the air trap and vent 3. Overflow from the air trap and vent 3 goes to drain 35.

A flow control valve 4 provides the desired flow and flow meter 5 monitors the flow of water. The water passes through the normally open solenoid valve 6. During sterilization of the system the norm-ally open valve 6 is closed and the manually operated by-pass valve 7 is preset to provide about one-fourth the flow of water which is heated to a much higher temperature. Automatic reduction of water flow during sterilization is an important feature resulting in reduction of heater size, cost, and power requirements.

The water is supplied to an electric heater 8 which produces water at the desired temperature, approximately 37 C. for normal dialysis and approximately 95 C. for sterilization. Thermistor sensing circuitry 9 is provided for controlling the heater 8, that is, varying the electric current to obtain the desired heating. Thermistor circuitry 10 monitors the water temperature and actuates an alarm relay when the water temperature is outside of normal limits.

A controllable volume pump 13 supplies dialysate concentrate from the reservoir 15 through the check valve 12 to the mixer 11.

The mixed water and concentrate passes through the concentration control element 18 on its way to the dialyzer. The concentration control element 18 is a conductivity cell which produces an electrical signal representing the concentration of the dialysate fluid supplied from the mixer 11. The electrical signal produced by the conductivity cell is applied to the pump 13 to control the volume of concentrate supplied to the mixer 11 so that the concentration of the dialysate fluid remains constant. The control circuitry for this control loop is shown in block form in FIG. 2. A secondary speed control loop is provided for the pump 13. This control loop includes a tachometer 33 driven at the same speed as the pump 13. The tachometer 33 produces an electrical signal representing the speed of the pump and this is applied to maintain the speed of the pump constant regardless of variations other than conductivity changes.

Another conductivity cell 19 is provided for monitoring the conductivity of the dialysate fluid. The dialysate fluid is supplied to the constant head vessel 20. The head vessel 20 has an overflow outlet 21 coupled through a drain cup 24 to the gravity drain 35.

The head vessel 20 provides a supply of dialysate fluid at a constant pressure to the dialyzer. The dialysate fluid is supplied through pressure control valve 25 to the inlet dialysate port of the dialyzer which may be of the Kiil type, for example. In this type of dialyzer, blood ports are provided for passage of blood on one side of a membrane and dialysate ports are provided for passage of dialysate fluid on the other side of the membrane. The dialysate fluid passes through the dialyzer on one side of the membrane and out through the outlet dialysate port.

A pressure gauge 27 is provided to monitor the negative pressure at the outlet of the dialyzer. Flow meter 28 is provided to monitor the flow rate through the dialyzer and blood leak detector 29 is provided to sense the presence of blood in the dialysate fluid.

A vacuum breaker 30 is provided so that if the system becomes clogged, a large negative pressure which might break the membrane will not be applied to the dialyzer. The eflluent pump 32 applies the negative pressure through check valve 31, and regulates dialysate flow through the dialyzer.

All of the monitors are connected to shut off the efiluent pump 32 and stop dialysate flow through the dialyzer when any of the monitored conditions exceed the preset limits. The temperature monitor thermistor circuit 10, the conductivity monitor 19, over-temperature sensor 23, pressure gauge 27, and blood leak detector 29 are all monitoring circuits of the type in which a set of relay contacts are activated when the monitored condition exceeds its adjustable preset limits. All of these relay contacts are connected in a circuit to control the volt power for the eflluent pump 32. When any monitored condition exceeds its limits the relay contacts will be activated and power will be cut off to the pump 32.

Also included in this control circuit is a level monitoring probe, 22, of the conductivity type located in the head vessel. If dialysate make-up rate becomes less than the flow rate to the dialyzer, the level drop in the head vessel is sensed and the efiluent pump 32 turned ofi.

In addition to, or in place of, the concentration monitor 19, an Ag, AgCl detector may be provided. Such a detector would similarly be connected to monitor the chloride content of the dialysate fluid and turn oil the pump 32 when the concentration is outside the desired limits. The silver, silver chloride detector could also be used in place of concentration control element 18 to control the pump 13.

The system is electrically programmed to automatically proceed through the following steps; rinse, pre-sterilize, normalize, monitor test, alarm test, system test, dialyze, after-sterilize. The control system and monitors are interlocked to prevent the flow of anything other than normal dialysate to the dialyzer.

The system for controlling the pump 13 in accordance with the control signal from the concentration monitor can be of well known type. One suitable system is shown in block form in FIG. 2. The conductivity cell includes a sensor 36 for determining conductivity. Another sensor 37 which is temperature sensitive, provides temperature compensation for the conductivity cell 36. The sensors 36 and 37 are connected in a bridge circuit 38. Variations in the conductivity from a given setpoint produce an error signal which is amplified in amplifier 39. The phase detector 40 senses the phase of the error signal which is an indication of whether the conductivity is above or below the setpoint. The error signal is compared with an adjustable setpoint in the setpoint control 41.

The error signal from the setpoint control 41 is compared with the signal from tachometer 33 in the error comparator 42. The resultant signal is amplified in error amplifier 43 and power amplifier 44 and is used to drive the servo motor 45. As is conventional, there is feedback from the servo motor 45 to the error amplifier 43. The servo motor 45 drives the concentrate pump 13 to provide the desired volume of concentrate to the mixing chamber 11.

What is claimed is:

1. A blood dialysis system comprising:

a dialyzer having a membrane, blood ports for passage of blood through said dialyzer on one side of said membrane and dialysate ports for passage of dialysate fluid through said dialyzer on the other side of said membrane,

a source of dialysate concentrate,

a mixer for mixing said water and said dialysate concentrate to produce dialysate fluid, said dialysate fluid being supplied from said mixer to said dialysate ports,

a controllable volume electrically driven pump connected to continuously supply dialysate concentrate from said source of concentrate to said mixer,

a conductivity cell continuously producing an electrical signal representing the concentration of the dialysate fluid supplied from said mixer to said dialysate ports,

means for applying said electrical signal to said pump to control the volume of concentrate supplied to said mixer so that the concentration of said dialysate fluid remains constant,

a tachometer driven at the same speed as said pump, said tachometer producing a tachometer signal representing the speed of said pump, and

means for applying said tachometer signal to maintain the speed of said pump constant.

2. The system recited in claim 1 further comprising:

an eflluent pump for supplying said dialysate fluid from said mixer to said dialysate ports,

means for monitoring the conditions of the dialysate fluid, and

means responsive to said monitoring means for deenergizing said efliuent pump when any monitored condition exceeds preset limits.

3. The system recited in claim 2 wherein said monitoring means includes:

a temperature monitor,

a conductivity monitor,

a pressure gauge, and

a blood leak detector, each having a set of relay contacts which are activated when the monitored condition exceeds preset limits, said relay contacts being connected in a circuit to control the application of power to said eflluent pump.

4. A blood dialysis system comprising:

a dialyzer having a membrane, blood ports for passage of blood through said dialyzer on one side of said membrane and dialysate ports for passage of dialysate fluid through said dialyzer on the other side of said membrane,

a source of water,

a source of dialysate concentrate,

a mixer for mixing said water and said dialysate concentrate to produce dialysate fluid, said dialysate fluid being supplied from said mixer to said dialysate ports,

a controllable volume, constant speed, electrically driven pump connected to continuously supply dialysate concentrate from said source of concentrate to said mixer,

a conductivity cell continuously producing an electrical signal representing the concentration of the dialysate fluid supplied from said mixer to said dialysate ports,

a heater connected between said source of water and said mixer,

a normally open solenoid valve connected between said source of water and said heater from supplying a normal flow of Water to said heater during dialysis, said normally open valve being closed during sterilization of said system,

a bypass around said normally open valve, and

a bypass valve in said bypass, said bypass valve being preset to provide about one-fourth said normal flow of water to said heater during sterilization so that said water is heated to a much higher temperature during sterilization.

References Cited UNITED STATES PATENTS 3,352,779 11/1967 Austin et al. 2l0-23 3,406,826 10/1968 Willock 210321 X 3,416,664 12/1968 Kumme et a1. 210l03 X REUBEN FRIEDMAN, Primary Examiner F. A. SPEAR, JR., Assistant Examiner US. Cl. X.R.

gg ggg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,508,656 Dated 'Mhv 11. 1910 Inventor) EARL J. SERFASS and VERNON H. TROUTNER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 16, change "top" to tap- Column 4 line 56, after "membrane," indent and insert -a source of water,-

SIGNED M521 SEALED (SEAL) mm: 1:. sum, an. Edward u M I! Gomisaiomr of Patents Attestin Oifioar

Images