Adaptive filter flow control system and method

• US 5,069,792 A
• Filed: 07/10/1990
• Issued: 12/03/1991
• Est. Priority Date: 07/10/1990
• Status: Expired due to Term

• Current Assignee: Baxter International Inc.
• Original Assignee: Baxter International Inc.
• Inventors: Callaway, William D., Prince, Paul R.
• Primary Examiner(s): Sever, Frank
• Application Number:
  US07/551,598
• Time in Patent Office: 511 Days
• Field of Search: 210/651, 210/929, 210/637, 210/85, 210/87, 210/90, 210/433.1, 604/4-6
• US Class Current: 210/637
• CPC Class Codes: A61M 1/262 rotating
• CPC Class Codes: A61M 1/34 Filtering material out of the blood by passing it through a membrane, i.e. hemofiltration or diafiltration
• CPC Class Codes: A61M 1/3403 Regulation parameters
• CPC Class Codes: A61M 1/341 by measuring the filtrate rate or volume
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: B01D 61/22 Controlling or regulating

Abstract

An adaptive filter concentrate flow control system and method includes a filter system, a pumping system driving feed fluid, concentrate and filtrate flowing through the filter system and a flow control system controlling the pumping system to maintain optimum filtrate flow rates or minimum feed flow rates along a control surface in a three dimensional transmembrane pressure--feed fluid rate--filtrate flow rate space. Actual sensed operating point data is used to locate the control surface so as to assure an optimized filtrate flow rate or minimized feed flow rate at which reversible blocking of the membrane has begun to occur without irreversible blocking or plugging. The system is advantageously employed to control and maximize the flow of plasma in a plasmapheresis system or to minimize the rate at which blood is withdrawn from a donor and introduced into the system while achieving a fixed rate of plasma flow.

Claims

1. A fluid flow control system for controlling a flow of filtrate through a filter system having a filter membrane with a predictable transmembrane pressure-filtrate flow rate-feed flow rate relationship when the filter system is operated under nonobstructing operating conditions, the control system comprising:

means for substantially precluding irreversible blocking of said filter membrane including,

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system in response to at least one control signal;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

means for maintaining the transmembrane pressure at an operating point lying upon a particular three dimensional control surface having a shape conforming to the predictable transmembrane pressure-filtrate flow rate-feed flow rate relationship, and a pressure offset from the received pressure indication by a selected pressure difference.

2. The fluid flow control system according to claim 1 above, wherein the predictable transmembrane pressure-filtrate and transmembrane pressure-feed flow rate relationships are substantially linear so that pressure increases with filtrate and feed flow rates.

3. The fluid flow control system according to claim 2 above, wherein the fluid flow control system is operable to determine an actual nonobstructing transmembrane pressure-operating point during each filtration cycle and to determine the predictable transmembrane pressure-filtrate flow rate-feed flow rate relationship as a plane passing through the determined actual operating point and having a first slope reflecting the feed flow versus pressure fluid characteristics of the system and a second slope reflecting the filtrate flow versus pressure fluid characteristic of the system.

4. The fluid flow control system according to claim 2 above, wherein the fluid flow control system is operable to determine a plurality of actual nonobstructing transmembrane pressure operating points dependent upon actual feed fluid, fluid pumping system, and filter membrane characteristics encountered during each filtration cycle and determine the predictable transmembrane pressure-filtrate flow-feed flow relationship as a plane passing through the determined actual operating points.

5. The fluid flow control system according to claim 1 above, wherein the fluid flow control system is operable to collect data defining an actual nonobstructing transmembrane pressure operating point during each filtration cycle and to determine the particular control surface in response to the collected actual operating point data.

6. The fluid flow control system according to claim 5 above, wherein the first and second slopes are different and the pressure offset is empirically derived and reflects the physical characteristics of the filter system and the feed fluid.

7. The fluid flow control system according to claim 1 above, wherein the fluid flow control system is operable to determine a plurality of actual nonobstructing transmembrane pressure operating points dependent upon actual feed fluid, fluid pumping system, and filter membrane characteristics encountered during each filtration cycle and to determine the particular control surface in response to the determined actual operating points.

8. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a concentrate pump coupled to pump concentrate fluid from the filter system and the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the concentrate pump.

9. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a feed fluid pump operating to pump feed fluid to the filter system and a concentrate pump coupled to pump concentrate fluid from the filter system and wherein the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the concentrate pump relative to the flow rate of the feed fluid pump.

10. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a feed fluid pump operating to pump feed fluid to the filter system and a filtrate pump coupled to pump filtrate fluid from the filter system and wherein the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the filtrate pump relative to the flow rate of the feed fluid pump.

11. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a feed fluid pump operating to pump feed fluid to the filter system and a filtrate pump coupled to pump filtrate fluid from the filter system and wherein the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the feed pump relative to the flow rate of the filtrate fluid pump.

12. A fluid flow control system comprising:

means for substantially precluding irreversible blocking of said filter membrane including,

a filter system having a filter membrane with a predictable transmembrane pressure-filtrate flow rate-feed flow rate relationship when the filter system is operated under nonobstructing operating conditions;

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

means for maintaining transmembrane pressure at an operating point lying upon a particular three dimensional control surface having a shape conforming to the predictable transmembrane pressure-filtrate flow rate-feed flow rate relationship and a pressure offset from the indicated transmembrane pressure by a selected pressure difference.

13. A filter fluid flow control system comprising:

means for substantially precluding irreversible blocking of said filter, including,

means for filtering coupled to receive and filter a feed fluid, the filtering means including a porous separator separating filtrate fluid from the feed fluid to produce concentrate fluid, the flow of filtrate fluid through the membrane having a predictable pressure surface characteristic for nonobstructing filtering conditions;

means for pumping disposed to control the flow of feed fluid, concentrate fluid and filtrate fluid in the filtering means;

means for sensing the indicating pressure differential across the separator; and

means for maintaining the pressure across the separator and filtrate fluid flow rate at a point lying upon a flow control surface having a shape conforming to the predictable pressure surface characteristic and a pressure offset relative to at least one nonobstructing filter condition actual system operating point.

14. The filter fluid control system according to claim 13 above, wherein the feed fluid is blood, the concentrate is packed cells, and the filtrate is plasma, and wherein the flow rate of plasma is controlled relative to the flow rate of blood and wherein the pressure offset is empirically derived and reflects the physical characteristics of the filter system and of the blood.

15. The filter fluid control system according to claim 13 above, wherein the porous separator is a rotating membrane and the filtrate has a centripetal flow direction through the rotating membrane.

16. A filter fluid flow control system comprising:

means for substantially precluding irreversible blocking of said filter membrane including,

means for filtering coupled to receive and filter a feed fluid, the filtering means including a porous separator separating filtrate fluid from the feed fluid to produce concentrate fluid, the flow of filtrate fluid through the membrane having a predictable three dimensional pressure-filtrate flow rate-feed flow rate surface characteristic for nonobstructing filtering conditions;

means for pumping disposed to control the flow of feed fluid, concentrate fluid and filtrate fluid in the filtering means;

means for sensing and indicating pressure differential across the separator; and

means for maintaining the pressure across the separator and feed fluid flow rate at a point lying upon a flow control surface having a shape conforming to the predictable surface characteristic and a selected pressure offset relative to at least one nonobstructing filter condition actual system operating point.

17. The filter fluid control system according to claim 16 above, wherein the feed fluid is blood, the concentrate is packed cells, and the filtrate is plasma, and wherein the flow rate of plasma is controlled relative to the flow rate of blood and wherein the pressure offset is selected to locate the system operating point in the regime of reversible filter blocking.

18. The filter fluid control system according to claim 16 above, wherein the porous separator is a rotating membrane and the filtrate has a centrifugal flow direction through the rotating membrane.

19. The method of optimizing a flow of filtrate through a filter comprising the steps of:

providing means for substantially precluding irreversible blocking of said filter by,

determining a three dimensional flow rate control surface in a three dimensional filtrate flow rate versus transmembrane pressure versus feed flow rate coordinate system, the control surface having a shape conforming to sensed nonobstructing concentrate flow rate versus transmembrane pressure characteristic and a predetermined pressure offset;

determining said value; and

controlling the filter operating point to produce filter operation at a point which lies upon the flow rate control surface.

20. A method of optimizing flow of filtrate through a filter comprising the steps of:

providing means for substantially precluding irreversible blocking of said filter by,

determining a three dimensional flow rate control surface in a filtrate flow rate versus transmembrane pressure versus feed flow rate coordinate system, the control surface having a shape conforming to a sensed nonobstructing transmembrane pressure characteristic and a selected pressure offset, the control surface being determined by detecting at least one nonobstructing actual filter operating point and using as the know nonobstructing transmembrane pressure characteristic a three dimensional prediction surface passing through the detected at least one nonobstructing actual filter operating point;

determining said value; and

automatically controlling the filter operating point to produce filter operation at a point which lies upon the flow rate control surface.

21. The method according to claim 20 above, wherein the prediction surface is a plane in the three dimensional coordinate system.

22. The method according to claim 20 above, wherein the detecting step detects exactly one nonobstructing actual filter operating point and the prediction plane has a first slopes reflecting the feed flow versus pressure fluid characteristic of the system and a second slope reflecting the filtrate flow versus pressure fluid characteristic of the system.

23. The method according to claim 20 above, wherein the detecting step detects exactly two nonobstructing actual filter operating points and the prediction surface is a plane and passes through the two detected nonobstructing actual filter operating points.

24. The filter system according to claim 20 above, wherein the pumping system includes a feed fluid pump pumping the feed fluid and wherein the fluid flow control system operates to command operation of the feed fluid pump at a commanded feed fluid velocity and to further control the operation of the pumping system to tend to reduce the pressure difference in response to a product of the integral of the pressure difference and the commanded feed fluid velocity.

25. The filter system according to claim 24 above, wherein the pumping system includes a flow rate efficiency correction to further maximize the safe operating filtrate flow rate.

26. The filter system according to claim 25 above, wherein the feed is blood and the filtrate is plasma.

27. An adaptive flow filter system comprising:

a filter receiving a flow of feed fluid and separating the received feed fluid to produce separate flows of concentrate fluid and filtrate fluid;

means for substantially precluding irreversible blocking of said filter including,

a pumping system coupled to cause the feed fluid, concentrate fluid and filtrate fluid to flow at controlled flow rates;

a pressure sensor coupled to sense and indicate any pressure differential between the received feed fluid and filtrate fluid; and

means for controlling said pumping system operable in a three dimensional pressure versus feed fluid flow rate versus filtrate flow rate coordinate system to determine at lest one filter system actual operating point and to determine from the at least one actual operating point a control surface having a pressure offset relative to a locus of anticipated nonblocking actual operating points, said means for controlling said pumping system being operable to control the pumping system in response to a pressure difference as indicated by the pressure sensor between an actual sensed pressure at an operating point having known feed and filtrate flow rates and a pressure at a point on the control curve having corresponding feed and filtrate flow rates to tend to reduce the pressure difference, these relationships being scaled linearly with feed fluid flow rates.

28. The filter system according to claim 27 above wherein the fluid flow control system operates to integrate the pressure difference and control the pumping system in response to the integral of the pressure difference.

29. An adaptive flow filter system comprising:

a filter receiving a flow of feed fluid and separating the received feed fluid to produce separate flows of concentrate fluid and filtrate fluid;

means for substantially precluding irreversible blocking of said filter including,

a pumping system coupled to cause the feed fluid, concentrate fluid and filtrate fluid to flow at controlled flow rates;

a pressure sensor coupled to sense and indicate any pressure differential between the received feed fluid and filtrate fluid; and

means for controlling said pumping system operable in a three dimensional pressure versus feed fluid flow rate versus filtrate flow rate coordinate system to determine at least one filter system actual operating point and to determine from the at least one actual operating point a control surface having a pressure offset relative to a locus of anticipated nonblocking actual operating points, said means for controlling said pumping system being operable to control the pumping system in response to a pressure difference as indicated by the pressure sensor between an actual sensed pressure at an operating point having known feed and filtrate flow rates and a pressure at a point on the control curve having corresponding feed and filtrate flow rates to tend to reduce the pressure difference, these relationships being scaled linearly with filtrate fluid flow rates.

30. The filter system according to claim 29 above wherein the fluid flow control system operates to integrate the pressure difference and control the pumping system in response to the integral of the pressure difference.

31. The filter system according to claim 30 above, wherein the pumping system includes a filtrate fluid pump pumping the filtrate fluid and wherein the fluid flow control system operates to command operation of the filtrate fluid pump at a commanded filtrate fluid velocity and to further control the operation of the pumping system to tend to reduce the pressure difference in response to a product of the integral of the pressure difference and the commanded filtrate fluid velocity.

32. The filter system according to claim 31 above, wherein the pumping system includes a flow rate efficiency correction to further minimize the safe operating feed flow rate.

33. The filter system according to claim 32 wherein the feed is blood and the filtrate is plasma.

34. The filter system according to claim 33 wherein the filter is a spinning membrane filter.

35. A fluid flow control system for controlling a flow of filtrate through a filter system having a filter membrane with a predictable transmembrane pressure-filtrate flow rate-feed flow rate relationship when the filter system is operated under nonobstructing operating conditions, the control system comprising:

means for substantially precluding irreversible blocking of said filter membrane including,

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system in response to at least one control signal;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

means for maintaining the transmembrane pressure at an operating point lying upon a particular three dimensional control surface having a shape conforming to the predictable transmembrane pressure-filtrate flow rate-feed minus filtrate flow rate relationships, and a pressure offset from the received pressure indication by a selected pressure difference.