Wideband external pulse cardiac monitor

• US 5,913,826 A
• Filed: 06/12/1996
• Issued: 06/22/1999
• Est. Priority Date: 06/12/1996
• Status: Expired due to Fees

• Current Assignee: K-NFB Reading Technology Inc.
• Original Assignee: K-NFB Reading Technology Inc.
• Inventors: Blank, Seymour
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US08/661,910
• Time in Patent Office: 1,105 Days
• Field of Search: 600/485, 600/493-6, 600/500-507, 600/526, 600/450, 600/547
• US Class Current: 600/500
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02208 using the Korotkoff method
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
• 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 5/412 Detecting or monitoring sepsis
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 7/045 Detection of Korotkoff sounds A61B5/0225 takes precedence; measuring blood pressure A61B5/021

Abstract

An apparatus for assessing cardiovascular status of a mammal comprising a system for locally applying a pressure to an artery, capable of restricting blood flow through said artery, a wideband external pulse transducer, having an output, situated to measure acoustic signals proximate to said artery, and a computing device receiving said output for calculating, based on said output, a peripheral vascular impedance value. The systolic and diastolic pressure are determined by an appearance and disappearance of a high frequency signal upon changes in cuff pressure partially occluding arterial blood flow. The arterial pressure waveform is estimated by measuring the wideband acoustic emissions from a non-occluded artery. The peak and trough of the arterial pressure waveform are calibrated with the determined systolic and diastolic pressures. The systemic vascular resistance is computed by occluding blood flow with a supersystolic pressure, and calculating, based on a natural logarithm of a difference in amplitude between a first major systolic peak and first major systolic trough and an amplitude of a second major systolic peak, a first order linear equation, which may be normalized for body surface area. The data obtained may also be used to analyze cardiac output, arterial compliance and dp/dt.

Claims

1. An apparatus for assessing cardiovascular status of a mammal comprising:

a system for locally applying a pressure to an artery, capable of restricting blood flow through said artery;

a wideband external pulse transducer, having an output, situated to measure acoustic signals proximate to said artery; and

a computing device receiving said output for calculating based on said output measured during a period of completely occluded flow through said artery, a peripheral vascular impedance value.

2. The apparatus according to claim 1, wherein said value is a peripheral vascular resistance.

3. The apparatus according to claim 1, said computing device further calculating a peripheral vascular resistance based on said value and a biometric factor relating to the mammal.

4. The apparatus according to claim 3, wherein said biometric factor relates to a body surface area of the mammal.

5. The apparatus according to claim 3, wherein said biometric factor relates to a size of a vascular tree of the mammal.

6. The apparatus according to claim 1, wherein said computing device analyzes a temporal amplitude pattern of said output.

7. The apparatus according to claim 6, wherein said system for locally applying a pressure to an artery occludes said artery, said temporal amplitude pattern comprising a pair of adjacent amplitude peaks and an intervening dip, the computing device calculating a ratio of the amplitude difference of first peak and intervening dip, and the second peak.

8. The apparatus according to claim 7, wherein the computing device calculates said value as a linear first order function of the natural logarithm of said ratio.

9. The apparatus according to claim 8, wherein the value corresponds to the peripheral vascular resistance indexed for body surface area, said linear first order function approximating 714 mm Hg dyne sec cm^-5 m^-2 minus 250 times a natural logarithm of said ratio.

10. The apparatus according to claim 9, wherein said computing device further calculates a peripheral vascular resistance by correcting for body surface area.

11. The apparatus according to claim 1, wherein said value varies with peripheral vascular resistance and body surface area.

12. The apparatus according to claim 1, wherein said system for locally applying a pressure to an artery has at least two states, a first state in which said artery is occluded and a second state in which arterial blood flow is partially occluded.

13. The apparatus according to claim 12, wherein said computing device controls a state of said system for locally occluding arterial blood flow.

14. The apparatus according to claim 12, wherein said computing device determines a blood pressure based on said output and a state of said system for locally applying a pressure to an artery.

15. The apparatus according to claim 14, wherein said blood pressure is determined as a systolic and a diastolic pressure.

16. The apparatus according to claim 12, wherein said system for locally applying a pressure to an artery has a third state which does not occlude arterial blood flow, said computing device determining an arterial pulse pressure waveform based on said output.

17. The apparatus according to claim 16, wherein said computing device calculates a mean arterial pressure based on said arterial pulse pressure waveform.

18. The apparatus according to claim 17, wherein said computing device calculates a value relating to cardiac output based on said mean arterial pressure and said value.

19. The apparatus according to claim 18, wherein said computing device calculates a heart rate and value relating to stroke volume from said heart rate and said cardiac output.

20. The apparatus according to claim 16, wherein said output, when said system for locally occluding arterial blood flow is in said non-occlusive state, is analyzed by said computing device to determine a value relating to arterial compliance.

21. The apparatus according to claim 20, wherein said computing device compensates said peripheral vascular impedance value for body surface area.

22. The apparatus according to claim 21, wherein said output has a downsloping amplitude period, said value relating to said arterial compliance being determined as an exponential timeconstant of said downsloping amplitude period divided by said peripheral vascular impedance value compensated for body surface area.

23. The apparatus according to claim 1, wherein said computing device further calculates a mean arterial blood pressure compensated for arterial pulse pressure waveform.

24. The apparatus according to claim 1, wherein said computing device analyzes said output to determine a change in arterial pressure over time.

25. The apparatus according to claim 24, wherein said computing device determines a value relating to cardiac contractility from said change in arterial pressure over time.

26. The apparatus according to claim 1 wherein said wideband external pulse transducer comprises a foil electret transducer.

27. The apparatus according to claim 1 wherein said wideband external pulse transducer comprises a metalized polyvinylidene fluoride polymer film.

28. A method for determining a peripheral vascular impedance of a mammal, comprising the steps of:

measuring a WEP waveform of a peripheral artery with blood flow occluded;

measuring a difference in amplitude between a first major systolic peak and first major systolic trough and measuring an amplitude of a second major systolic peak;

determining a ratio of a difference between said first major peak and said first major trough and said second major peak; and

determining, based on the determined ratio, a peripheral vascular impedance.

29. The method according to claim 28, further comprising the step of determining a biometric factor of the mammal, and compensating the peripheral vascular impedance to determine a peripheral vascular resistance.

30. The method according to claim 29, wherein the biometric factor is body surface area.

31. The method according to claim 28 further comprising the step of determining an intraarterial pressure waveform by measuring a wideband external pressure waveform over a peripheral artery with a blood flow therethrough not occluded and calibrating said determined waveform with a maximum systolic and minimum diastolic pressures as determined by partial occlusion with an externally applied pressure.

32. The method according to claim 31, further comprising the step of determining a cardiac output based on the intraarterial waveform and the peripheral vascular impedance.

33. A noninvasive cardiac monitoring apparatus comprising:

a brachial artery cuff;

pressure control system for controlling a pressure in said cuff;

a wideband acoustic transducer, having an output, for measuring acoustic emission proximate to said cuff, and

a system for analyzing said output at least during a period of complete occlusion of flow in the brachial artery due to pressurization of said cuff, to determine peripheral vascular impedance.

34. The apparatus according to claim 33, further comprising a system for determining a mean arterial pressure from said output.

35. The apparatus according to claim 34, further comprising a system for calculating cardiac output.

36. The system according to claim 33 wherein said acoustic transducer comprises a metalized electret polyvinylidene fluoride polymer film.

37. The apparatus according to claim 33, wherein said analyzing system comprises means for determining a peripheral vascular impedance based on said output while said cuff is held at a supersystolic pressure.

38. The apparatus according to claim 37, wherein said analyzing system comprises means for:

measuring a WEP waveform of a peripheral artery with blood flow occluded; and

measuring a ratio of a difference in amplitude between a first major systolic peak and first major systolic trough and an amplitude of a second major systolic peak.

39. The apparatus according to claim 38, wherein said estimating means analyzes a first order linear equation relating a natural logarithm of the determined ratio and the peripheral vascular resistance indexed for body surface area.

40. The apparatus according to claim 33, further comprising means for determining mean arterial pressure.

41. The apparatus according to claim 33, further comprising means for determining cardiac output.

42. A method for assessing cardiovascular status of a mammal comprising:

providing a system for locally applying a pressure to an artery, capable of restricting blood flow through said artery;

providing a wideband external pulse transducer, having an output, situated to measure acoustic signals proximate to said artery; and

analyzing the output of the wideband external pulse transducer, at least during a period of complete arterial occlusion, for the mammal based on a derived relation between diagnostic or prognostic clinical data and widehand external pulse transducer data for a population of mammals.

43. The method according to claim 42, wherein said derived relation comprises an artificial neural network.

44. The method according to claim 42, wherein said derived relation comprises a polynomial algorithm relating characteristics of the wideband external pulse transducer output with a diagnostic or prognostic clinical data value.

45. The method according to claim 42, wherein said analysis of the derived relation determines a likely diagnosis or prognosis of the mammal.

46. The method according to claim 42, wherein said analyzing step includes the substep of calculating, based on the output of the wideband external pulse transducer, a peripheral vascular impedance value.

47. The method according to claim 42, wherein said analysis of the derived relation estimates a blood flow through an artery proximate to the wideband external pulse transducer.

48. The method according to claim 42, wherein said analysis of the derived relation estimates a compliance of an artery proximate to the wideband external pulse transducer.

49. The method according to claim 42, wherein said analysis of the derived relation includes analysis of wideband external pulse transducer data obtained while arterial blood flow proximate to the transducer is partially occluded.

50. The method according to claim 42, wherein said analysis of the derived relation includes analysis of wideband external pulse transducer data obtained while arterial blood flow proximate to the transducer is occluded.

51. An apparatus for assessing cardiovascular status of a mammal comprising:

a system for selectively and completely occluding blood flow through a peripheral artery;

a wideband external pulse transducer, having an output, situated to measure acoustic signals proximate to said artery; and

a processor, for estimating, based on said output, a cardiovascular organ tone.

52. The apparatus according to claim 51, wherein said cardiovascular organ tone comprises cardiac contractility.

53. The apparatus according to claim 51, wherein said processor estimates the cardiovascular organ tone of the mammal, based on said output over a plurality of pulse cycles and a plurality of differing degrees of arterial restriction.

54. The apparatus according to claim 53, wherein said cardiovascular organ tone comprises a peripheral vascular impedance.

55. A method for assessing a cardiovascular status of a mammal, comprising the steps of:

providing data relating to a predetermined relationship of cardiovascular status with a set of pulse waveform amplitudes at at least three distinct pulse phases, corresponding to characteristic points of the pulse waveform, of a peripheral artery at a position proximate to a selectively controlled restriction of flow through the peripheral artery, for a population of mammals of the same species, the predetermined relationship comprising a mathematical function, having as a parameter a ratio of two different mathematical functions of at least one of the pulse waveform amplitudes;

measuring, during the distinct pulse phases, waveform amplitudes of a peripheral artery of a member of the species of mammal at a position proximate to a selectively controlled restriction of flow through the artery;

determining, according to the predetermined relationship, the cardiovascular status of the member of the species of mammal.

56. The method according to claim 55, wherein said mathematical function, has as a parameter a ratio of an amplitude difference between two peaks and a trough in the pulse waveform.

57. The method according to claim 55, wherein the pulse waveform is measured non-invasively and the restriction of flow through said peripheral artery is caused by a selectively applied external compression, the mathematical function defining the predetermined relationship further comprising a surface area of the member of the species of the mammal and measured pulse waveforms under at least two different degrees of arterial compression.