Estimation of stroke volume cardiac output using an intracardiac pressure sensor

• US 20030199779A1
• Filed: 04/22/2002
• Published: 10/23/2003
• Est. Priority Date: 04/22/2002
• Status: Active Grant

• Current Assignee: Chester Struble, Lambert Muhlenberg
• Original Assignee: Chester Struble, Lambert Muhlenberg
• Inventors: Struble, Chester, Muhlenberg, Lambert
• Granted Patent: US 7,024,244 B2
• Time in Patent Office: Days
• US Class Current: 600/513
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/36564 controlled by blood pressure
• CPC Class Codes: A61N 1/36571 controlled by blood flow rate, e.g. blood velocity or cardiac output

Abstract

Techniques are described for estimating a rate of blood flow from a heart, such as a stroke volume or a cardiac output, as a function of a pressure in the heart. A pressure monitor may measure pressure values, and identify the times at which pressure values and valve opening and closing occur. The pressure monitor may estimate a velocity-time function as a function of the measured pressures and identified times, and may calculate a velocity-time integral by integrating the velocity-time function. The pressure monitor may also calculate an estimated velocity-time integral directly as a function of the measured pressures and the identified times. The pressure monitor may calculate the stroke volume or cardiac output using the velocity-time integral. The pressure monitor may control a delivery of therapy by an implantable medical device as a function of the stroke volume or cardiac output.

Claims

1. An implantable medical device comprising:

an input circuit that receives a pressure signal representative of a pressure within a heart; and

a processor that calculates a change in the pressure as a function of the pressure signal, and estimates a rate of blood flow from the heart as a function of the change in the pressure.

2. The device of claim 1, wherein the device is implanted in the upper chest of a patient.

3. The device of claim 1, wherein the processor estimates a velocity-time integral as a function of the change in the pressure, and calculates the rate as a function of the velocity-time integral.

4. The device of claim 1, wherein the processor estimates velocity data as a function of the change in pressure, and determines the rate as a function of the velocity data.

5. The device of claim 4, wherein the processor calculates a peak velocity as a function of the pressure signal, and estimates velocity data as a function of the peak velocity.

6. The device of claim 1, wherein the processor identifies a pressure value at a time of valve opening and a peak pressure value as a function of the pressure signal, and wherein the processor calculates the change in the pressure as a difference between the peak pressure value and the pressure value at the time of valve opening.

7. The device of claim 6, wherein the processor identifies a point of maximum positive slope of the pressure signal, and wherein the pressure value at the time of valve opening is a pressure value of the pressure signal at the point of maximum positive slope.

8. The device of claim 7, wherein the processor generates a differential signal that is representative of the first derivative of the pressure signal as a function of the pressure signal, and wherein the point of maximum positive slope of the pressure signal is a point of the pressure signal corresponding to a point of the differential signal where a maximum value of the differential signal occurs.

9. The device of claim 6, wherein the processor identifies a peak of the pressure signal, and wherein the peak pressure value is a pressure value at the peak.

10. The device of claim 1, wherein the processor determines time data as a function of the pressure signal, and estimates the rate as a function of the time data and the change in the pressure.

11. The device of claim 10, wherein the time data comprises a time of valve opening and a time of valve closing.

12. The device of claim 11, wherein the pressure monitor identifies a point of maximum positive slope of the pressure signal, and sets the time of valve opening as a time at the point of maximum positive slope.

13. The device of claim 12, wherein the processor generates a differential signal that is representative of the first derivative of the pressure signal as a function of the pressure signal, and wherein the point of maximum slope of the pressure signal is a point of the pressure signal corresponding to a point of the differential signal where a maximum value of the differential signal occurs.

14. The device of claim 11, wherein the processor identifies a point of maximum negative slope of the pressure signal, and sets the time of valve closing as a time at the point of maximum negative slope.

15. The device of claim 14, wherein the processor generates a differential signal that is representative of the first derivative of the pressure signal as a function of the pressure signal, and

wherein the point of maximum negative slope of the pressure signal is a point of the pressure signal corresponding to a point of the differential signal where a minimum value of the differential signal occurs.

16. The device of claim 11, wherein the processor calculates a duration of a time period between the time of valve opening and the time of valve closing and estimates the rate as a function of the duration.

17. The device of claim 5, wherein the processor determines time data as a function of the pressure signal, and estimates the velocity data as a function of the peak velocity and the time data.

18. The device of claim 17, wherein the time data comprises a time of valve opening, a time of peak pressure and a time of valve closing, and

wherein the processor estimates velocity data as a function of the peak velocity, the time of valve opening, the time of peak pressure and the time of valve closing

19. The device of claim 18, wherein the pressure monitor identifies a point of maximum positive slope of the pressure signal, and

wherein the time of valve opening is a time at the point of maximum positive slope.

20. The device of claim 19, wherein the processor generates a differential signal that is representative of the first derivative of the pressure signal as a function of the pressure signal, and

wherein the point of maximum slope of the pressure signal is a point of the pressure signal corresponding to a point of the differential signal where a maximum value of the differential signal occurs.

21. The device of claim 18, wherein the processor identifies a peak of the pressure signal, and

wherein the time of peak pressure is a time at which the peak occurs.

22. The device of claim 18, wherein the processor identifies a point of maximum negative slope of the pressure signal, and

wherein the time of valve closing is a time at the point of maximum negative slope.

23. The device of claim 22, wherein the processor generates a differential signal that is representative of the first derivative of the pressure signal as a function of the pressure signal, and

wherein the point of maximum negative slope of the pressure signal is a point of the pressure signal corresponding to a point of the differential signal where a minimum value of the differential signal occurs.

24. The device of claim 18, wherein the processor determines a time of peak velocity as a function of the time of peak pressure and estimates velocity data as a function of the time of valve opening, the time of peak velocity, the peak velocity and the time of valve closing.

25. The device of claim 4, wherein the processor integrates the velocity data and determines the rate as a function of a result of the integration.

26. The device of claim 1, wherein the rate is a stroke volume.

27. The device of claim 1, wherein the rate is a cardiac output.

28. The device of claim 16, wherein the input circuit further receives an electrical activity signal, the electrical activity signal a function of electrical activity within the heart, and

wherein the processor calculates a heart rate as a function of the electrical activity signal and determines the cardiac output as a function of the heart rate and the velocity-time integral.

29. The device of claim 1, further comprising a memory,

wherein the processor stores the rate in the memory.

30. The device of claim 1, further comprising an input/output circuit coupled to the processor, the input/output circuit configured to exchange information between a person and the processor.

31. A method comprising:

sensing a pressure within a heart;

calculating a change in the pressure; and

determining a rate of blood flow from the heart as a function of the change in pressure.

32. The method of claim 31, wherein calculating the change in the pressure comprises:

identifying a pressure value at a time of valve opening as a function of the pressure;

identifying a peak pressure value as a function of the pressure; and

calculating the difference between the peak pressure value and the pressure value at the time of valve opening.

33. The method of claim 32, wherein identifying the pressure value at the time of valve opening comprises:

identifying a point of maximum positive slope of a pressure signal, the pressure signal a function of the pressure; and

identifying a pressure value at the point of maximum positive slope of the pressure signal.

34. The method of claim 33, wherein identifying the point of maximum positive slope of the pressure signal comprises:

generating a first derivative of the pressure signal; and

identifying a point on the pressure signal at which the first derivative of the pressure signal is maximized.

35. The method of claim 32, wherein identifying peak pressure value comprises:

identifying a peak of a pressure signal, the pressure signal a function of the pressure; and

identifying a pressure value at the peak.

36. The method of claim 31, further comprising determining time data as a function of the pressures,

wherein estimating the rate as a function of the change in pressure comprises estimating the rate as a function of the change in pressure and the time data.

37. The method of claim 36, wherein determining time data comprises:

identifying a time of valve opening as a function of the pressures; and

identifying a time of valve closing as a function of the pressures.

38. The method of claim 37, wherein identifying the time of valve opening comprises:

identifying a point of maximum positive slope of a pressure signal, the pressure signal a function of the pressures; and

identifying a time at the point of maximum positive slope of the pressure signal.

39. The method of claim 38, wherein identifying the point of maximum positive slope of the pressure signal comprises:

generating a first derivative of the pressure signal; and

identifying a point on the pressure signal at which the first derivative of the pressure signal is maximized.

40. The method of claim 37, wherein identifying the time of valve closing comprises:

identifying a point of maximum negative slope of a pressure signal, the pressure signal a function of pressure in the heart; and

identifying a time at the point of maximum negative slope of the pressure signal.

41. The method of claim 40, wherein identifying the point of maximum negative slope of the pressure signal comprises:

generating a first derivative of the pressure signal; and

identifying a point on the pressure signal at which the first derivative of the pressure signal is minimized.

42. The method of claim 37, further comprising calculating a duration of a time period between the time of valve opening and the time of valve closing,

wherein estimating the rate as a function of the change in pressure comprises estimating the rate as a function of the change in pressure and the duration.

43. The method of claim 31, further comprising estimating a velocity-time integral as a function of the change in pressure,

wherein estimating the rate as a function of the change in pressure comprises calculating the rate as a function of the velocity-time integral.

44. The method of claim 31, further comprising estimating velocity data as a function of the change in pressure,

wherein estimating the rate as a function of the change in pressure comprises estimating the rate as a function of the velocity data.

45. The method of claim 44, wherein estimating velocity data comprises:

calculating a peak velocity as a function of the change in pressure; and

estimating velocity data as a function of the peak velocity.

46. The method of claim 45, wherein estimating velocity data as a function of the change in pressure further comprises determining time data as a function of the pressure in the heart, and estimating velocity data as a function of the peak velocity comprises estimating velocity data as a function of the peak velocity and the time data.

47. The method of claim 46, wherein determining time data comprises:

identifying a time of valve opening as a function of the pressures;

identifying a time of peak pressure as a function of the pressures; and

identifying a time of valve closing as a function of the pressures.

48. The method of claim 47, wherein identifying the time of valve opening comprises:

identifying a point of maximum positive slope of a pressure signal, the pressure signal a function of the pressures; and

identifying a time at the point of maximum positive slope of the pressure signal.

49. The method of claim 48, wherein identifying the point of maximum positive slope of the pressure signal comprises:

generating a first derivative of the pressure signal; and

identifying a point on the pressure signal at which the first derivative of the pressure signal is maximized.

50. The method of claim 47, wherein identifying the time of peak pressure comprises:

identifying a peak of a pressure signal, the pressure signal a function of the pressure; and

identifying a time at which the peak occurs.

51. The method of claim 47, wherein identifying the time of valve closing comprises:

identifying a point of maximum negative slope of a pressure signal, the pressure signal a function of pressure in the heart; and

identifying a time at the point of maximum negative slope of the pressure signal.

52. The method of claim 51, wherein identifying the point of maximum negative slope of the pressure signal comprises:

generating a first derivative of the pressure signal; and

identifying a point on the pressure signal at which the first derivative of the pressure signal is minimized.

53. The method of claim 47, wherein estimating velocity data as a function of the peak velocity and the time data comprises:

determining a time of peak velocity as a function of the time of peak pressure; and

estimating velocity data as a function of the time of valve opening, the time of peak velocity, the peak velocity and the time of valve closing.

54. The method of claim 44, wherein determining the rate comprises:

integrating the velocity data; and

determining the rate as a function of a result of the integration.

55. The method of claim 31, wherein estimating the rate comprises estimating a stroke volume as a function of the change in pressure.

56. The method of claim 31, wherein estimating the rate comprises estimating a cardiac output as a function of the change in pressure.

57. The method of claim 56, wherein estimating the cardiac output further comprises:

calculating a heart rate; and

estimating the cardiac output as a function of the heart rate and the change in pressure.

58. The method of claim 31, further comprising storing the rate in memory.

59. The method of claim 31, further comprising transmitting the rate to a device external to the body that contains the heart.

60. The method of claim 31, further comprising controlling a delivery of therapy by an implantable medical device as a function of the rate.

61. The method of claim 60, wherein controlling the delivery of therapy by the implantable medical device comprises controlling a delivery of pacing pulses by a pacemaker.

62. The method of claim 60, wherein controlling the delivery of therapy by the implantable medical device comprises controlling a delivery of drugs by a drug pump.