Capacitance fluid volume measurement

• US 7,107,837 B2
• Filed: 01/22/2002
• Issued: 09/19/2006
• Est. Priority Date: 01/22/2002
• Status: Expired due to Fees

• Current Assignee: Baxter Healthcare SA (Baxter International Inc.), Baxter International Inc.
• Original Assignee: Baxter Healthcare SA (Baxter International Inc.), Baxter International Inc.
• Inventors: Childers, Robert W., Din, Shahid, Lauman, Brian, Kienman, Rick, Hopping, Pete
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): FRANK, RODNEY T
• Application Number:
  US10/054,487
• Publication Number:
  US 20030136189A1
• Time in Patent Office: 1,701 Days
• Field of Search: 733/04.C, 731/49, 731/68, 738/61, 738/610.4, 732/32, 732/62, 732/63, 732/90.R
• US Class Current: 73/304.00C
• 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 1/154 with sensing means or components thereof
• 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 1/159 specially adapted for peritoneal dialysis
• CPC Class Codes: A61M 1/1658 Degasification
• CPC Class Codes: A61M 1/28 Peritoneal dialysis ; Other peritoneal treatment, e.g. oxygenation
• CPC Class Codes: A61M 1/284 Continuous flow peritoneal dialysis [CFPD]
• CPC Class Codes: A61M 1/287 Dialysates therefor
• CPC Class Codes: A61M 2205/3317 Electromagnetic, inductive or dielectric measuring means
• CPC Class Codes: A61M 2205/3379 Masses, volumes, levels of fluids in reservoirs, flow rates
• CPC Class Codes: A61M 5/14216 Reciprocating piston type
• CPC Class Codes: A61M 5/14224 Diaphragm type
• CPC Class Codes: A61M 5/16831 Monitoring, detecting, signalling or eliminating infusion flow anomalies low-level float-valves causing cut-off A61M5/40; indicating or recording presence, absence or direction of flow in general G01P13/0066
• CPC Class Codes: G01F 23/263 by measuring variations in capacitance of capacitors

Abstract

A fluid volumetric pumping system has a fluid pump and capacitor plates disposed around a pump chamber of the fluid pump. The capacitance between the capacitor plates changes as the volume of fluid in the pump chamber changes. An electrical circuit measures a change in the capacitance between the plates and outputs a signal indicative of the volume of fluid in the pump chamber. The pump having the capacitance sensor of the present invention fluidly connects to a patient. In an embodiment, a peritoneal dialysis system provides dialysate to the patient via the pump, and the capacitance sensor measures the volume of dialysate supplied to and drained from a peritoneal cavity of the patient.

Claims

1. A device for providing dialysis solution to a to a patient comprising:

a fluid receptacle, the fluid receptacle having a substantially hollow interior and defining an exterior surface;

a membrane receptacle adapted to receive dialysis solution, the membrane receptacle carried within the substantially hollow interior of the fluid receptacle;

at least two capacitor plates positioned adjacent to the exterior surface of the fluid receptacle, the at least two capacitor plates arranged in an opposing manner;

a circuit electrically connected to the at least two capacitor plates, the circuit configured to produce an output signal indicative of a volume of the dialysis solution in the membrane receptacle; and

a member for providing at least a portion of the dialysis solution within the membrane receptacle to or from a patient.

2. The device of claim 1, wherein the membrane receptacle operates with a pump chamber having at least one fluid port.

3. The device of claim 2, wherein the capacitor plates have a shape that is substantially the same as the shape of the pump chamber.

4. The device of claim 1, wherein the membrane receptacle includes at least one flexible membrane wall movable to pump medical fluid.

5. The device of claim 1, wherein the membrane receptacle includes first and second flexible membrane walls, at least one of the first and second membrane walls being movable to change a volume of the receptacle.

6. The device of claim 1, wherein the membrane receptacle includes a portion of a disposable dialysis fluid flow path useable with a dialysis machine.

7. The device of claim 1, wherein at least one capacitor plate a non-planer shape.

8. The device of claim 1, wherein the capacitor plates have a shape at least substantially the same as the exterior surface of the fluid receptacle.

9. The device of claim 1, wherein the circuit charges the capacitor plates and measures a change in voltage from the capacitor plates over a time interval.

10. The device of claim 1, wherein the circuit further comprises:

a ground connection to one of the capacitor plates; and

a capacitance sensor circuit connected to another capacitor plate.

11. The device of claim 1, which includes a pair of substantially parallel capacitor plates.

12. A device for providing dialysis to a patient comprising:

a plurality of capacitor plates defining a space between the plates;

a fluid receptacle for holding a volume of dialysis fluid positioned within the space, the receptacle having a flexible membrane receptacle adapted to receive the dialysis fluid and operable to enable a relatively low dielectric fluid to be present at certain times between the receptacle and the plates;

a circuit electrically connected to the plurality of capacitor plates, the circuit having an output indicative of the volume of dialysis fluid in the fluid receptacle; and

a fluid line coupled to the patient to deliver at least a portion of the volume of dialysis fluid to or from the patient.

13. A device for providing continuous flow peritoneal dialysis comprising:

a fluid receptacle;

a flexible dialysis receptacle disposed within the fluid receptacle, the dialysis receptacle capable of being placed in fluid communication with a patient;

first and second capacitor plates defining a space within and between which the fluid receptacle is located, the plates having a variable dielectric between the plates that is dependent on an amount of fluid in the dialysis receptacle; and

an electrical circuit connected to the capacitor plates that creates a signal that is related to the variable dielectric.

14. A system for measuring a volume of a fluid to be provided to or from a patient, the system comprising:

a fluid receptacle, the fluid receptacle carrying a flexible membrane receptacle capable of being fluidly connected to a patient;

first and second capacitor plates defining a space within and between which the fluid receptacle is located, the plates having a variable dielectric between the plates that is dependent on an amount of a fluid in the flexible membrane receptacle; and

an electrical circuit connected to the capacitor plates that creates a signal that is related to the variable dielectric.

15. The system of claim 14, wherein the signal is indicative of the volume of the fluid in the flexible membrane receptacle.

16. The system of claim 14, wherein the signal is indicative of a volume of air in the fluid receptacle.

17. The system of claim 14, wherein the signal is indicative of a portion of fluid in the flexible membrane receptacle and a portion of air in the fluid receptacle.

18. The system of claim 14, wherein the fluid receptacle operates inside of a fluid pump chamber.

19. The system of claim 18, wherein the capacitor plates have a shape substantially the same as the fluid pump chamber.

20. The system of claim 14, wherein the fluid receptacle is positioned between the first and second capacitor plates.

21. The system of claim 14, further comprising a pump piston, wherein one of the first and second capacitor plates defines an aperture that allows a portion of the piston to extend outside the plate.

22. The system of claim 14, further comprising a pump piston, wherein the pump piston moves between the capacitor plates.

23. The system of claim 14, further comprising a displacement fluid that expands and contracts the flexible membrane receptacle to fill and empty the fluid in and out of the receptacle.

24. The system of claim 14, wherein the fluid receptacle includes a pump chamber wall defining a port that can apply a negative pressure to the flexible membrane receptacle and pull at least a portion of one of the membranes towards the port.

25. The system of claim 14, wherein the fluid receptacle includes a pair of pump chamber walls each defining a port.

26. The system of claim 14, wherein at least one of the first and second capacitor plates is represented by the surface of the adjacent fluid.

27. The system of claim 14, wherein the flexible membrane receptacle is part of a disposable cassette.

28. The system of claim 14, further comprising a processor that determines a volume of the fluid from the signal outputted by the electrical circuit.

29. The system of claim 14, further comprising a processor that determines a cumulative volume of fluid from a plurality of individual volumes of fluid in the fluid receptacle.

30. The system of claim 14, wherein the pair of capacitor plates have a shape substantially the same as the receptacle when the receptacle is full of fluid.

31. A system for measuring a volume of a fluid to be provided to or from a patient, the system comprising:

a fluid receptacle;

first and second capacitor plates positioned outside of and on opposing sides of the fluid receptacle;

a flexible membrane receptacle carried within the fluid receptacle, the flexible membrane in fluid communication with the patient; and

an electrical circuit providing a voltage source that enables a signal indicative of the volume of the fluid in the receptacle to be generated.

32. The system of claim 31, wherein the output signal is based on at least one of:

a variable dielectric between the plates, a changing surface area of one of the plates, and a changing distance between the plates.

33. The system of claim 31, wherein the signal is based on a varying dielectric constant between the fluid and air.

34. The system of claim 31, wherein the circuit charges the capacitor plates and measures a change in voltage from the capacitor plates over a time interval.

35. The system of claim 34, wherein the time interval is a fixed time interval.

36. A medical fluid delivery system, comprising:

a fluid flow path including a patient connection;

a membrane receptacle positioned inside a chamber, the membrane receptacle so constructed and arranged to be in fluid communication with the fluid flow path; and

a capacitance sensor positioned on opposing sides of an outer surface of the chamber and capable of accounting for an amount of a relatively low dielectric fluid existing between the membrane receptacle and the chamber to indicate a volume of fluid in the receptacle.

37. The system of claim 36, wherein the chamber is a pump chamber.

38. The system of claim 37, wherein the capacitance sensor further comprises first and second capacitor plates at opposite sides of the pump chamber.

39. The system of claim 38, wherein the capacitor plates have a shape substantially the same as part of the pump chamber.

40. The system of claim 36, wherein the capacitance sensor further comprises first and second capacitor plates positioned at opposite sides of the fluid receptacle.

41. The system of claim 36, wherein the capacitance sensor includes at least one capacitor plate having a non-planer shape.

42. The system of claim 36, wherein the membrane receptacle is part of a disposable set.

43. The system of claim 36, wherein the capacitance sensor comprises first and second capacitor plates and an electrical circuit connected to the plates.

44. The system of claim 36, wherein the pair of capacitor plates have a shape substantially the same as the fluid receptacle when the fluid receptacle is substantially full of fluid.

45. The system of claim 36, wherein the medical fluid delivery system is a dialysis system.

46. The system of claim 45, wherein the dialysis system is a continuous flow peritoneal dialysis system.

47. A dialysis system, comprising:

a fluid flow mechanism having a flexible membrane receptacle arranged to hold and convey a fluid during a dialysis treatment; and

a fluid volume capacitance sensor having first and second capacitor plates each positioned and arranged on an opposing side of the fluid flow mechanism to measure a volume of the fluid conveyed by the flexible membrane receptacle during the dialysis treatment.

48. The dialysis system of claim 47, wherein the fluid flow mechanism is a continuous flow mechanism capable of performing continuous flow dialysis.

49. The dialysis system of claim 47, wherein the fluid flow mechanism is fluidly connected to a peritoneal dialysis catheter.

50. The dialysis system of claim 47, wherein the fluid flow mechanism is fluidly connected to a plurality of peritoneal access lumens.

51. A method of measuring a volume of a medical fluid pumped by a fluid pump, comprising the steps of:

configuring a plurality of capacitor plates to define a space between the plates;

sensing a first state of a medical fluid receptacle located within the space when a flexible membrane receptacle within the medical fluid receptacle is substantially empty of fluid so that a relatively low dielectric fluid exist between the plates and the receptacle;

providing the medical fluid to the flexible membrane receptacle;

sensing a second state of the fluid receptacle with the capacitor plates when the flexible membrane is substantially full of medical fluid; and

determining a volume of the medical fluid in the fluid receptacle based on the first and second states sensed by the capacitor plates.

52. The method of claim 51 further comprising the steps of:

substantially emptying the flexible membrane receptacle of fluid; and

providing additional medical fluid to the flexible membrane receptacle, sensing another second state, and determining another volume of the medical fluid.

53. The method of claim 51, which includes continuously sensing the state of the flexible membrane receptacle as the fluid enters the fluid receptacle.

54. The method of claim 51, which includes determining a total volume of fluid from a plurality of volumes of medical fluid provided to the flexible membrane receptacle.

55. The method of claim 51, which includes knowing a total amount of medical fluid needed by a patient and stopping the provision of the medical fluid when the total amount has been provided.

56. The method of claim 51, which includes determining a volume of air in the fluid receptacle based on the first and second states sensed by the capacitor plates.

57. A method of providing dialysis to a patient, comprising the steps of:

measuring a volume of dialysis fluid having a sequentially changing inverse relationship with a relatively low dielectric fluid, the dialysis fluid located within a receptacle, the receptacle positioned within a space defined by first and second plates of a capacitance sensor; and

pumping a portion of the volume of the dialysis fluid into a portion of a patient using a flexible membrane supported within the receptacle.

58. The method of claim 57, wherein the portion includes a peritoneal cavity of the patient.

59. The method of claim 57, wherein the measuring step further comprises measuring the volume of dialysis fluid in a pump chamber.