FLUID VOLUME DETERMINATION FOR MEDICAL TREATMENT SYSTEM

• US 20110071465A1
• Filed: 01/23/2009
• Published: 03/24/2011
• Est. Priority Date: 01/23/2008
• Status: Active Grant

• Current Assignee: Deka Products Limited Partnership
• Original Assignee: DEKA Research & Development
• Inventors: Kamen, Dean, Wang, Tien-Shoe, McGill, David W.
• Granted Patent: US 8,197,439 B2
• Time in Patent Office: Days
• US Class Current: 604/67
• CPC Class Codes: A61M 1/14 Dialysis systems; Artificial kidneys; Blood oxygenators semi-permeable membranes characterised by the material, manufacturing processes therefor B01D71/00 ; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis
• CPC Class Codes: A61M 1/1522 the interface being evacuated interfaces to enhance contact
• CPC Class Codes: A61M 1/1524 the interface providing means for actuating on functional elements of the cassette, e.g. plungers
• CPC Class Codes: A61M 1/153 the cassette being adapted for heating or cooling the treating fluid, e.g. the dialysate or the treating gas
• CPC Class Codes: A61M 1/155 with treatment-fluid pumping means or components thereof
• CPC Class Codes: A61M 1/1561 at least one cassette surface or portion thereof being flexible, e.g. the cassette having a rigid base portion with preformed channels and being covered with a foil
• CPC Class Codes: A61M 1/1565 Details of valves
• CPC Class Codes: A61M 1/159 specially adapted for peritoneal dialysis
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1601 Control or regulation
• CPC Class Codes: A61M 1/1623 Disposition or location of membranes relative to fluids
• CPC Class Codes: A61M 1/1629 with integral heat exchanger
• CPC Class Codes: A61M 1/1631 having non-tubular membranes, e.g. sheets
• CPC Class Codes: A61M 1/166 Heating for sterilisation A61M1/1686
• CPC Class Codes: A61M 1/1694 with recirculating dialysing liquid
• CPC Class Codes: A61M 1/28 Peritoneal dialysis ; Other peritoneal treatment, e.g. oxygenation
• CPC Class Codes: A61M 1/281 Instillation other than by gravity
• CPC Class Codes: A61M 1/282 Operational modes
• CPC Class Codes: A61M 1/288 Priming priming in extracorporeal blood circuits A61M1/3643
• CPC Class Codes: A61M 2039/1066 having protection means, e.g. sliding sleeve to protect connector itself, shrouds to protect a needle present in the connector, protective housing, isolating sheath
• CPC Class Codes: A61M 2205/12 : with interchangeable cassettes forming partially or totally the fluid circuit
• CPC Class Codes: A61M 2205/121 : interface between cassette and base
• CPC Class Codes: A61M 2205/122 : using evacuated interfaces to enhance contact
• CPC Class Codes: A61M 2205/123 : with incorporated reservoirs
• CPC Class Codes: A61M 2205/127 : with provisions for heating or cooling
• CPC Class Codes: A61M 2205/128 : with incorporated valves
• CPC Class Codes: A61M 2205/13 : with means for the detection of operative contact with patient, e.g. lip sensor
• CPC Class Codes: A61M 2205/14 : Detection of the presence or absence of a tube, a connector or a container in an apparatus
• CPC Class Codes: A61M 2205/3306 : Optical measuring means
• CPC Class Codes: A61M 2205/3331 : Pressure; Flow
• CPC Class Codes: A61M 2205/3334 : Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/3379 : Masses, volumes, levels of fluids in reservoirs, flow rates
• CPC Class Codes: A61M 2205/36 : related to heating or cooling
• CPC Class Codes: A61M 2205/502 : User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2205/6036 : characterised by physical shape, e.g. array of activating switches
• CPC Class Codes: A61M 2209/08 : Supports for equipment
• CPC Class Codes: A61M 39/1011 : Locking means for securing connection; Additional tamper safeties A61M39/16 takes precedence
• CPC Class Codes: A61M 39/105 : Multi-channel connectors or couplings, e.g. for connecting multi-lumen tubes multi-channel connectors in general F16L37/56
• CPC Class Codes: A61M 39/20 : Closure caps or plugs for connectors or open ends of tubes
• CPC Class Codes: A61M 39/28 : Clamping means for squeezing flexible tubes, e.g. roller clamps tube strippers A61M1/83
• CPC Class Codes: A61M 39/281 : Automatic tube cut-off devices, e.g. squeezing tube on detection of air
• CPC Class Codes: A61M 5/16809 : by repeated filling and emptying of an intermediate volume pressure infusion using positive displacement pumps A61M5/142
• CPC Class Codes: A61M 5/16813 : by controlling the degree of opening of the flow line
• CPC Class Codes: A61M 5/16827 : controlling delivery of multiple fluids, e.g. sequencing, mixing or via separate flow-paths infusion of multiple fluids without using a controller A61M5/1407
• CPC Class Codes: F04B 43/0054 : particularities of the flexible members
• CPC Class Codes: F04B 43/02 : having plate-like flexible members, e.g. diaphragms F04B43/14 takes precedence
• CPC Class Codes: F04B 43/073 : the actuating fluid being controlled by at least one valve
• CPC Class Codes: F04B 43/08 : having tubular flexible members F04B43/12 takes precedence
• CPC Class Codes: F04B 43/086 : with two or more tubular flexible members in parallel F04B43/1136 takes precedence
• CPC Class Codes: F04B 53/22 : Arrangements for enabling ready assembly or disassembly
• CPC Class Codes: G16H 20/40 : relating to mechanical, radiation or invasive therapies, e.g. surgery, laser therapy, dialysis or acupuncture
• CPC Class Codes: G16H 40/63 : for local operation
• CPC Class Codes: Y02A 90/10 : Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A volume of fluid moved by a pump, such as a pump in an APD system, may be determined without direct measurement of the fluid, such as by flow meter, weight, etc. For example, a volume of a pump chamber (181) (having a movable element that varies the volume of the pump chamber) may be determined by measuring pressure in the pump chamber and a reference chamber, both while the two chambers are isolated from each other, and after the two chambers are fluidly connected so that pressures in the chambers may equalize. Equalization of the pressures may be assumed to occur in an adiabatic way, e.g., a mathematical model of the system that is based on an adiabatic pressure equalization process may be used to determine the pump chamber volume. In one embodiment, pressures measured after the chambers are fluidly connected may be measured at a time before complete pressure equalization has occurred, and thus the pressures for the pump and reference chambers measured after the chambers are fluidly connected may be unequal, yet still be used to determine the pump chamber volume.

Claims

1. A method for determining a volume of fluid moved by a pump, the method including:

measuring a first pressure for a pump control chamber when the pump control chamber is isolated from a reference chamber, the pump control chamber having a volume that varies at least in part based on movement of a portion of the pump;

measuring a second pressure for the reference chamber when the reference chamber is isolated from the pump control chamber, the reference chamber having a known volume;

measuring a third pressure associated with the pump control chamber after fluidly connecting the reference chamber and the pump control chamber, but before substantial equalization of pressures between the pump control and reference chambers has occurred;

measuring a fourth pressure associated with the reference chamber after fluidly connecting the reference chamber and the pump control chamber, but before substantial equalization of pressures between the pump control and reference chambers has occurred;

determining a volume for the pump control chamber based on the first, second, third and fourth measured pressures.

2. The method of claim 1, wherein the third and fourth pressures are measured at approximately a same time and the third and fourth pressures are substantially unequal to each other.

3. The method of claim 1, wherein the step of determining includes:

using a model for determining the volume of the pump control chamber that assumes an adiabatic system from a point in time when the first and second pressures are measured for the isolated pump control chamber and the reference chamber until a point in time when the third and fourth pressures are measured.

4. The method of claim 1, wherein equalization of the pressures in the pump control and reference chambers occurs after an equalization time period after the pump control and reference chambers are fluidly connected, and wherein the third and fourth pressures are measured at a time after the pump control and reference chambers are fluidly connected that is approximately 10% to 50% of the equalization time period.

5. The method of claim 1, wherein steps of measuring the first, second, third and fourth pressures and the step of determining are performed for two different positions of a pump membrane to determine two different volumes for the pump control chamber, and a difference between the two different volumes represents a volume of fluid delivered by the pump.

6. The method of claim 1, wherein the pump is part of a disposable cassette and the pump control chamber is part of a dialysis machine used in a dialysis procedure.

7. The method of claim 1, wherein a time period between measurement of the first and second pressures and measurement of the third and fourth pressures is minimized.

8. The method of claim 1, wherein the first pressure is selected from a plurality of pressure measurements as coinciding with a point in time at which a pressure in the pump control chamber first begins to change from a previously stable value.

9. The method of claim 1, wherein the second pressure is selected from a plurality of pressure measurements as coinciding with a point in time at which a pressure in the reference chamber first begins to change from a previously stable value.

10. The method of claim 8, wherein the point in time is identified based on a determination of when a best fit line for a plurality of consecutive sets of measured pressures first deviates from a constant slope.

11. The method of claim 1, wherein the step of measuring the third and fourth pressures comprises:

measuring a plurality of pressure values for the pump control chamber after the pump control and reference chambers are fluidly connected;

determining a plurality of change in volume values for the pump control chamber based on the plurality of pressure values for the pump control chamber, each of the plurality of change in volume values corresponding to a unique point in time and a measured pressure value for the pump chamber;

measuring a plurality of pressure values for the reference chamber after the pump control and reference chambers are fluidly connected;

determining a plurality of change in volume values for the reference chamber based on the plurality of pressure values for the reference chamber, each of the plurality of change in volume values corresponding to a unique point in time and a measured pressure value for the reference chamber;

determining a plurality of difference values between change in volume values for the pump control chamber and for the reference chamber, each difference value being determined for a change in volume value for the pump control chamber and a change in volume value for the reference chamber that correspond to a same or substantially same point in time; and

identifying the third and fourth pressures as being equal to the pump control chamber pressure value and the reference chamber pressure value that correspond to a difference value that is below a threshold.

20. The method of claim 1, wherein the pressures measured are pressures of a gas within the pump control chamber and the reference chamber, the equalization of pressures within the pump control chamber and reference chamber is assumed to occur adiabatically, the equalization of pressures between the pump control chamber and reference chamber is assumed to include a change in the volume of a gas in the pump control chamber and reference chamber in equal but opposite directions, and the volume of gas in the reference chamber at the time of the fourth pressure measurement is calculated from the known volume of the reference chamber, and the second and fourth pressures.

21. The method of claim 20, wherein the change in volume of gas in the reference chamber is assumed to be the difference between the known volume of the reference chamber and the calculated value of the volume of gas in the reference chamber at the time of the fourth pressure measurement.

22. The method of claim 21, wherein the change in volume of gas in the pump control chamber is assumed to be the difference between the initial volume of the pump control chamber and the volume of gas in the pump control chamber at the time of the third pressure measurement, wherein the change in volume of gas in the pump control chamber is equal to but opposite the change in volume of gas in the reference chamber.

12. A method for determining a volume of fluid moved by a pump, the method including:

providing a fluid pump apparatus having a pump chamber separated from a pump control chamber by a movable membrane, and a reference chamber that is fluidly connectable to the pump control chamber;

adjusting a first pressure in the pump control chamber to cause the membrane to move and thereby move fluid in the pump chamber;

isolating the reference chamber from the pump control chamber and establishing a second pressure in the reference chamber that is different from a pressure in the pump control chamber;

fluidly connecting the reference chamber and the pump control chamber to initiate equalization of pressures in the pump control chamber and the reference chamber; and

determining a volume for the pump control chamber based on the first and second pressures, and an assumption that the pressures in the pump control and reference chambers initiate equalization in an adiabatic way.

13. The method of claim 12, further comprising:

measuring third and fourth pressure the pump control and reference chambers, respectively, after fluidly connecting the reference chamber and the pump control chamber, and using the third and fourth pressures to determine the volume for the pump control chamber.

14. The method of claim 12, further comprising repeating the adjusting, isolating, fluidly connecting and determining steps, and determining a difference between the two determined volumes for the pump control chamber, where the difference represents a volume of fluid delivered by the pump.

15. The method of claim 12, wherein the pump is part of a disposable cassette and the pump control chamber is part of a dialysis machine used in a dialysis procedure.

16. The method of claim 12, wherein the first pressure is selected from a plurality of pressure measurements as coinciding with a point in time at which a pressure in the pump control chamber first begins to change from a previously stable value.

17. The method of claim 12, wherein the second pressure is selected from a plurality of pressure measurements as coinciding with a point in time at which a pressure in the reference chamber first begins to change from a previously stable value.

18. The method of claim 16, wherein the point in time is identified based on a determination of when a best fit line for a plurality of consecutive sets of measured pressures first deviates from a zero slope.

19. The method of claim 13, wherein the third and fourth pressures are substantially unequal to each other.

23. A medical infusion system, comprising:

a pump control chamber;

a control surface associated with the pump control chamber so that at least a portion of the control surface is movable in response to a pressure change in the pump control chamber;

a fluid handling cassette having at least one pump chamber positioned adjacent the control surface and arranged so that fluid in the at least one pump chamber moves in response to movement of the portion of the control surface;

a reference chamber that is fluidly connectable to the pump control chamber;

a control system arranged to adjust a pressure in the pump control chamber and thus control movement of fluid in the pump chamber of the fluid handling cassette, the control system being arranged to measure a first pressure for the pump control chamber when the pump control chamber is isolated from the reference chamber, measure a second pressure for the reference chamber when the reference chamber is isolated from the pump control chamber, fluidly connect the pump control chamber and the reference chamber, measure third and fourth pressures associated with the pump control chamber and the reference chamber, respectively, after fluidly connecting the reference chamber and the pump control chamber, and determine a volume for the pump control chamber based on the first, second, third and fourth measured pressures and a mathematical model that defines equalization of pressure in the pump control and reference chambers as occurring adiabatically when the pump control and reference chambers are fluidly connected.

24. The system of claim 23, wherein the third and fourth pressures are substantially unequal to each other.

25. The system of claim 23, wherein the third and fourth pressures are measured prior to substantial equalization of pressures in the pump control and reference chambers.

26-27. -27. (canceled)

28. A method for determining a presence of air in a pump chamber, the method including:

measuring a pressure for a pump control chamber when the pump control chamber is isolated from a reference chamber, the pump control chamber having a known volume and being separated from a pump chamber, that is at least partially filled with liquid, by a membrane;

measuring a pressure for the reference chamber when the reference chamber is isolated from the pump control chamber, the reference chamber having a known volume;

measuring a pressure after fluidly connecting the reference chamber and the pump control chamber and prior to a time when the pressure in the chambers has equalized; and

determining a presence or absence of an air bubble in the pump chamber based on the measured pressures and known volumes.

29. The method of claim 28, wherein a model used to determine the presence or absence of an air bubble assumes an adiabatic system from a point in time when the pressures are measured for the isolated pump control chamber and the reference chamber until a point in time after the chambers are fluidly connected.

30. The method of claim 29, wherein the pressure for the pump control chamber is measured with the membrane drawn toward a wall of the pump control chamber.