Methods, apparatus and articles-of-manufacture for noninvasive measurement and monitoring of peripheral blood flow, perfusion, cardiac output biophysic stress and cardiovascular condition

• US 20030135124A1
• Filed: 08/16/2002
• Published: 07/17/2003
• Est. Priority Date: 08/17/2001
• Status: Active Grant

• Current Assignee: Ted W. Russell
• Original Assignee: Ted W. Russell
• Inventors: Russell, Ted W.
• Granted Patent: US 7,192,403 B2
• Time in Patent Office: Days
• US Class Current: 600/500
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• 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 5/7257 using Fourier transforms

Abstract

The invention relates to methods, apparatus, articles-of-manufacture, and coded data signals for measuring cardiac output, limb blood flow, perfusion, blood pressure, artery elasticity, and cardiovascular deterioration and disease, including performing these measurements on a continuous heart beat-by-beat basis, for humans and animals. Unlike empirical methods of other noninvasive blood pressure concepts, the invention is grounded on scientifically appropriate hemodynamic principles that studies have validated as accurate, and is practical for wide clinical use. Devices constructed in accordance with the invention can be comfortably employed for numerous applications, including hospital monitoring, physician'"'"'s office cardiovascular disease management and drug therapy monitoring, home monitoring, and athletic applications.

The invention may be implemented in a variety of single or multi-sensor embodiments, such as: invasive pressure cannula sensor systems; non invasive pressure transducer arrays and piezo or other strain sensing materials that are placed against the skin above arteries; “upstream” pulsing-sensors (that apply single or multi-frequency vibrations that are measured “downstream” from the first placement location); other types of plethysmographic sensors; sonic/ultrasonic/Doppler sensors; MRI blood spin magnetizer/sensors; oxygen sensors; and electrocardiographic sensors, etc.

Claims

1. A method of continuous, noninvasive, hemodynamic monitoring, comprising:

receiving a signal related to pressure pulsations in a patient'"'"'s artery;

processing said signal, at least in part in the frequency domain, to obtain pressure and flow waveforms, and a composite phase lag between peaks in the pressure and flow waveforms.

2. A method as defined in claim 1, wherein processing is performed, and the waveforms computed, for each heartbeat i.

3. A method, as defined in claim 1, wherein processing includes computing a plurality of harmonic pressure components related to the received pressure signal.

4. A method, as defined in claim 3, wherein at least three harmonic pressure components are computed.

5. A method, as defined in claim 3, wherein said harmonic pressure components are computed using an FFT process.

6. A method, as defined in claim 1, wherein processing includes computing a pressure gradient along the longitudinal axis of said artery.

7. A method, as defined in claim 6, further comprising:

computing a plurality of harmonic components of said computed pressure gradient.

8. A method, as defined in claim 7, further comprising:

computing an estimate of flow velocity, on a harmonic-by-harmonic basis, using said harmonic components of said computed pressure gradient.

9. A method, as defined in claim 8, further comprising:

computing an estimate of the phase lag between the pressure and flow waveforms, by;

computing, for each harmonic of interest, a plurality of harmonic, flow-based elasticity waveforms, using a plurality of assumed phase shifts; and

,

identifying, for each harmonic of interest, the minimum phase shift which causes the corresponding harmonic components of the pressure and flow-based elasticity waveforms to peak at the same time.

10. A method, as defined in claim 9, further comprising:

computing a corrected flow velocity waveform, for each harmonic of interest, by adjusting the harmonic components of the previously-computed flow velocity waveform to incorporate the previously-computed minimum phase shift(s).

11. A method of estimating blood flow velocity, using a noninvasive pressure cuff, comprising:

receiving a pulsatile, pressure-related signal from said pressure cuff; and

,

computing, for each heartbeat cycle and each harmonic of interest, a first-pass estimate of harmonic phase velocity.

12. A method, as defined in claim 11, wherein computing a first-pass estimate of harmonic phase velocity, for each harmonic of interest, includes:

computing a first-pass group propagation velocity, said first-pass group propagation velocity being independent of harmonic frequency; and

,

for each harmonic of interest, adjusting said first-pass group propagation velocity, using harmonic-dependent factors, to produce said first-pass estimate of harmonic phase velocity.

13. A method, as defined in claim 12, wherein said harmonic-dependent factor(s) are non-linear function(s) of, at least, harmonic frequency-dependent, arterial radius-dependent and elasticity-dependent variables.

14. A method, as defined in claim 13, wherein said harmonic-dependent factor(s) include a Womersley modulus and Womersley phase factor, for each harmonic of interest.

15. A method of estimating blood flow velocity, using a noninvasive pressure cuff, comprising:

receiving a pulsatile, pressure-related signal from said pressure cuff;

computing, at least in part from said pressure-related signal, a pressure gradient-related waveform, for each heartbeat cycle;

computing harmonic component(s) of said pressure gradient-related signal, for each harmonic of interest; and

,

computing a first-pass estimate of blood flow, for each harmonic of interest, from, at least in part, said computed harmonic component(s).

16. A method, as defined in claim 15, wherein computing said pressure gradient-related waveform includes computing differences between successive samples of said pressure-related signal.

17. A method, as defined in claim 15, wherein computing harmonic component(s) of said pressure gradient-related waveform involves an FFT process.

18. A method, as defined in claim 15, wherein computing a first-pass estimate of blood flow includes computing a plurality of non-linear factors dependent, at least in part, on harmonic frequency, arterial radius and arterial elasticity.

19. A method, as defined in claim 18, wherein said non-linear factors include, at least, a Womersley modulus and Womersley phase factor, for each harmonic of interest.

20. A method for non invasively determining the longitudinal pressure gradient in a patient'"'"'s artery, comprising:

sampling a pressure-related signal obtained from an externally-mounted pressure-sensitive device;

computing said pressure gradient as a function, at least in part, of the difference between successive samples of said pressure-related signal.

21. A method, as defined in claim 20, wherein said externally-mounted, pressure-sensitive device is an inflatable cuff.

22. A method, as defined in claim 20, wherein said cuff is wrapped around a limb of the patient and inflated to a monitoring pressure of approximately 10-25 mmHg.

23. A method, as defined in claim 20, wherein said externally-mounted, pressure-sensitive device is a plethysmograph.

24. A method, as defined in claim 20, wherein computing said pressure gradient further includes:

computing an estimated propagation velocity from, at least in part, estimates of arterial wall thickness and elasticity; and

,

scaling said successive sample differences in inverse proportion to said estimated propagation velocity.

25. A method, as defined in claim 20, wherein computing said pressure gradient further includes scaling said successive sample differences in proportion to the sampling rate.

26. A method for computing blood flow in a patient'"'"'s artery, from a sequence of cuff pressure samples, comprising:

computing, for at least the first three harmonics of the patient'"'"'s heart rate, a first-pass harmonic phase velocity for each of said harmonic frequencies;

computing, from said sequence of cuff pressure samples, a first-pass pressure gradient waveform;

computing, for each of said at least first three harmonics, a frequency-domain modulus and phase of the first-pass pressure gradient waveform;

computing, for each of said at least first three harmonics, a first-pass harmonic flow waveform from, at least in part, the corresponding frequency-domain modulus and phase of said first-pass pressure gradient waveform;

computing, for each of said at least first three harmonics, a first-pass pressure-flow phase shift;

computing, for each of said at least first three harmonics, a second-pass estimate of harmonic phase velocity by correcting the corresponding first-pass harmonic phase velocity to account for the corresponding first-pass pressure-flow phase shift;

computing a final-pass pressure gradient waveform from, at least in part, said second-pass harmonic phase velocities; and

,

computing a final-pass flow velocity waveform from, at least in part, said final-pass pressure gradient waveform.

27. A method, as defined in claim 26, wherein computing a first-pass harmonic phase velocity for each of said harmonic frequencies includes:

computing a frequency-independent group propagation velocity; and

,

for each harmonic, adjusting said frequency-independent group propagation velocity, using harmonic-dependent factors, to produce said first-pass estimate of harmonic phase velocity.

28. A method, as defined in claim 27, wherein said harmonic-dependent factors are non-linearly dependent on, at least, harmonic frequency, arterial radius and arterial elasticity.

29. A method, as defined in claim 28, wherein said harmonic-dependent factors include a Womersley modulus and Womersley phase factor, computed for each harmonic of interest.

30. A method, as defined in claim 26, wherein computing, for each of said at least first three harmonics, a frequency-domain modulus and phase of the first-pass pressure gradient waveform involves an FFT process.

31. A method, as defined in claim 26, wherein computing, for each of said at least first three harmonics, a frequency-domain modulus and phase of the first-pass pressure gradient waveform involves a DFT process.

32. A method, as defined in claim 26, wherein computing a first-pass pressure gradient waveform includes computing differences between successive cuff pressure samples.

33. A method, as defined in claim 32, wherein computing a first-pass pressure gradient waveform further includes multiplying said successive sample differences by a scaling factor related to the ratio of sampling rate to estimated propagation velocity.

34. A method, as defined in claim 26, wherein computing said first-pass harmonic flow waveforms involves, for each harmonic, computing a sinusoidal waveform with frequency equal to the harmonic frequency, magnitude proportional, at least in part, to the corresponding harmonic pressure gradient modulus and phase offset, at least in part, by the corresponding harmonic pressure gradient phase.

36. A method, as defined in claim 26, wherein computing, for each of said at least first three harmonics, a first-pass pressure-flow phase shift includes:

computing, for each harmonic, a corresponding harmonic component of the cuff pressure sample waveform;

computing, for each harmonic, a plurality of incrementally phase-shifted flow-based elasticity waveforms; and

,

determining, for each harmonic, the first-pass pressure-flow phase shift by identifying the phase-shifted flow-based elasticity waveform whose peak corresponds most closely, in terms of phase, to the peak of the corresponding harmonic component of the cuff pressure sample waveform.

37. A method, as defined in claim 36, wherein computing, for each of said at least first three harmonics, a first-pass pressure-flow phase shift further includes interpolating, for each harmonic, between the closest matching incrementally phase-shifted flow-based elasticity waveforms to determine said pressure-flow phase shift.

38. A method, as defined in claim 26, wherein correcting the corresponding first-pass harmonic phase velocity to account for the corresponding first-pass pressure-flow phase shift includes multiplying said first-pass phase velocity by factors related to the first-pass pressure-flow phase shift and the relative position of the pressure peak in the cuff pressure sample waveform.

39. A method, as defined in claim 26, wherein computing a final-pass pressure gradient waveform includes:

for each harmonic;

computing a series of harmonic cuff pressure waveform samples; and

,

differencing successive harmonic cuff pressure samples, and scaling said differences by a scaling factor related to the ratio of the sampling rate to the corresponding second-pass harmonic phase velocity, to determine a final-pass harmonic component of the final-pass pressure gradient waveform;

then,

summing the final-pass harmonic components to determine the final-pass pressure gradient waveform.

35. A method, as defined in claim 35, wherein computing said first-pass harmonic flow waveforms involves, for each harmonic, further involves scaling the magnitude of the corresponding sinusoidal waveform by a corresponding Womersley modulus and offsetting the phase of said corresponding sinusoidal waveform by a corresponding Womersley phase factor.

40. A method of non invasively monitoring blood pressure and flow in a patient, comprising:

wrapping an inflatable cuff, having predetermined inflation characteristics, around the patient'"'"'s upper arm or a leg;

performing an oscillometric run by inflating the cuff to a flow-occluding pressure, then monitoring pressure pulsations over a series of successively lower inflation pressures;

using the predetermined inflation characteristics to convert the monitored pressure pulsations into equivalent volumetric pulsations;

determining initial-flow and zero-stress cuff inflation pressures; and

,

determining, at least in part from said initial-flow and zero-stress cuff inflation pressures, parameters related to arterial wall thickness and radius.

41. A method, as defined in claim 40, further comprising:

adjusting the inflation pressure in the cuff to a monitoring pressure of approximately 10-25 mmHg; and

,

determining arterial radius and elasticity at said monitoring pressure.

42. A method of continuously monitoring a plurality of hemodynamic parameters using a combination of time-domain and frequency-domain processing techniques, said method comprising:

computing, on a beat-by-beat basis, at least one time-domain parameter, selected from the list of;

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure;

wherein said at least one time-domain parameter is computed using time-domain processing techniques; and

,

computing, on a beat-by-beat basis, at least one frequency-domain parameter, selected from the list of;

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag;

wherein said at least one frequency-domain parameter is computed using, at least in part, frequency-domain processing techniques.

43. A method, as defined in claim 42, further comprising:

computing, on a beat-by-beat basis, at least one additional time-domain parameter, different from said at least one time-domain parameter, and selected from the list of;

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure;

wherein said additional time-domain parameter is computed using time-domain processing techniques.

44. A method, as defined in claim 42, further comprising:

computing, on a beat-by-beat basis, at least two additional time-domain parameters, different from said at least one time-domain parameter, and selected from the list of;

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure;

wherein said additional time-domain parameters are computed using time-domain processing techniques.

45. A method, as defined in claim 42, further comprising:

computing, on a beat-by-beat basis, at least three additional time-domain parameters, different from said at least one time-domain parameter, and selected from the list of;

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure;

wherein said additional time-domain parameters are computed using time-domain processing techniques.

46. A method, as defined in claim 42, further comprising:

computing, on a beat-by-beat basis, at least one additional frequency-domain parameter, selected from the list of;

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag;

wherein said at least one additional frequency-domain parameter is different from said frequency-domain parameter, and wherein said additional frequency-domain parameter is computed using, at least in part, frequency-domain processing techniques.

47. A method, as defined in claim 43, further comprising:

computing, on a beat-by-beat basis, at least one additional frequency-domain parameter, selected from the list of;

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag;

wherein said at least one additional frequency-domain parameter is different from said frequency-domain parameter, and wherein said additional frequency-domain parameter is computed using, at least in part, frequency-domain processing techniques.

48. A method, as defined in claim 44, further comprising:

computing, on a beat-by-beat basis, at least one additional frequency-domain parameter, selected from the list of;

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag;

wherein said at least one additional frequency-domain parameter is different from said frequency-domain parameter, and wherein said additional frequency-domain parameter is computed using, at least in part, frequency-domain processing techniques.

49. A method, as defined in claim 45, further comprising:

computing, on a beat-by-beat basis, at least one additional frequency-domain parameter, selected from the list of;

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag;

wherein said at least one additional frequency-domain parameter is different from said frequency-domain parameter, and wherein said additional frequency-domain parameter is computed using, at least in part, frequency-domain processing techniques.

50. A method of continuous, non invasive patient monitoring, comprising:

affixing a cuff to the upper arm or a leg of the patient;

performing a system calibration;

entering a beat-by-beat monitoring cycle, which includes;

providing a real-time blood pressure waveform; and

,

providing a real-time blood flow waveform computed, at least in part, in the frequency domain.

51. A method, as defined in claim 50, wherein said monitoring cycle further includes:

comparing parameters computed in the time and frequency domain to determine whether a system recalibration is needed; and

,

if needed, performing a system recalibration.

52. A method, as defined in claim 51, wherein the compared time-and frequency-domain parameters are related to arterial elasticity.

53. A method, as defined in claim 50, wherein the real-time blood pressure waveform is computed in the time domain.

54. A method, as defined in claim 53, wherein the real-time blood pressure signal is corrected, for visco-elastic pressure-flow phase lag, through use of a frequency-domain-computed correction factor.

55. A continuous, non invasive, hemodynamic monitoring system, comprising:

a pressure transducer, affixed to a patient'"'"'s upper arm or a leg, providing a signal related to pressure pulsations in a patient'"'"'s artery;

a signal processor, adapted to process said signal, at least in part in the frequency domain, to obtain pressure and flow waveforms, including a composite phase lag between peaks in the pressure and flow waveforms.

56. A system as defined in claim 55, wherein said signal processor operates on a heartbeat-by-heartbeat basis.

57. A system, as defined in claim 55, wherein said signal processor computes a plurality of harmonic pressure components related to the received pressure related signal.

58. A system, as defined in claim 57, wherein said signal processor computes at least the first three harmonic components of said pressure related signal.

59. A system, as defined in claim 57, wherein said signal processor includes an FFT processor.

60. A system, as defined in claim 55, wherein said signal processor includes a module programmed to compute a pressure gradient along the longitudinal axis of said artery.

61. A system, as defined in claim 60, wherein said signal processor further includes:

a pressure gradient FFT processing module, programmed to compute a plurality of harmonic components of said computed pressure gradient.

62. A system, as defined in claim 61, wherein said signal processor further includes:

a flow computation module, programmed to compute an estimate of flow velocity, on a harmonic-by-harmonic basis, using said harmonic components of said computed pressure gradient.

63. A system, as defined in claim 62, wherein said signal processor further includes:

a phase lag computation module, programmed to compute an estimate of the phase lag between the pressure and flow waveforms, by;

computing, for each harmonic of interest, a plurality of harmonic, flow-based elasticity waveforms, using a plurality of assumed phase shifts; and

,

identifying, for each harmonic of interest, the minimum phase shift which causes the corresponding harmonic components of the pressure and flow-based elasticity waveforms to peak at the same time.

64. A system, as defined in claim 63, wherein said signal processor further includes:

a velocity correction module, programmed to correct the flow velocity waveform(s), for each harmonic of interest, by adjusting the harmonic components of the previously-computed flow velocity waveform to incorporate the previously-computed minimum phase shift(s).

65. A non invasive system for estimating blood flow velocity, comprising:

a pressure cuff, providing a pulsatile, pressure-related signal; and

,

a signal processor, programmed to compute a first-pass estimate of harmonic phase velocity, for each heartbeat cycle and each harmonic of interest.

66. A system, as defined in claim 65, wherein said signal processor includes:

a first-pass group velocity computation module, programmed to compute a first-pass group propagation velocity, independent of harmonic frequency; and

,

a velocity-adjustment module, programmed to adjust, for each harmonic of interest, said first-pass group propagation velocity, using harmonic-dependent factors, to produce said first-pass estimate of harmonic phase velocity.

67. A system, as defined in claim 66, wherein said velocity-adjustment module employs harmonic-dependent factor(s) that are non-linear function(s) of, at least, harmonic frequency-dependent, arterial radius-dependent and elasticity-dependent variables.

68. A system, as defined in claim 67, wherein said harmonic-dependent factor(s) employed by said velocity-adjustment module include a Womersley modulus and Womersley phase factor, for each harmonic of interest.

69. A non invasive system for estimating blood flow velocity, comprising:

a pressure cuff, mounted to provide a pulsatile, pressure-related signal;

a pressure gradient processing module, programmed to compute, using, at least in part, said pressure-related signal, a pressure gradient-related waveform, for each heartbeat;

a harmonic processing module, programmed to compute harmonic component(s) of said pressure gradient-related signal, for each harmonic of interest; and

,

a flow processing module, programmed to compute a first-pass estimate of blood flow, for each harmonic of interest, using, at least in part, said computed harmonic component(s).

70. A system, as defined in claim 69, wherein said pressure gradient processing module computes differences between successive samples of said pressure-related signal.

71. A system, as defined in claim 69, wherein said harmonic processing module includes an FFT processing module.

72. A system, as defined in claim 69, wherein said flow processing module employs a plurality of non-linear factors dependent, at least in part, on harmonic frequency, arterial radius and arterial elasticity.

73. A system, as defined in claim 72, wherein said non-linear factors employed by said harmonic processing module include, at least, a Womersley modulus and Womersley phase factor, for each harmonic of interest.

74. A system for non invasively determining the longitudinal pressure gradient in a patient'"'"'s artery, comprising:

an externally-mounted pressure-sensitive device, providing a pressure-related signal;

a sampler, connected to provide samples of said pressure-related signal; and

,

a signal processor, programmed to compute said pressure gradient as a function, at least in part, of the difference between successive samples of said pressure-related signal.

75. A system, as defined in claim 74, wherein said externally-mounted, pressure-sensitive device is an inflatable cuff.

76. A system, as defined in claim 75, wherein said cuff is wrapped around a limb of the patient and inflated to a monitoring pressure of approximately 10-25 mmHg.

77. A system, as defined in claim 74, wherein said externally-mounted, pressure-sensitive device is a plethysmograph.

78. A system, as defined in claim 74, wherein said signal processor further includes:

means for computing an estimated propagation velocity from, at least in part, estimates of arterial wall thickness and elasticity; and

,

means for scaling said successive sample differences in inverse proportion to said estimated propagation velocity.

79. A system, as defined in claim 74, wherein said signal processor further includes means for scaling said successive sample differences in proportion to the sampling rate.

80. A computer-based system for computing blood flow in a patient'"'"'s artery, from a sequence of cuff pressure samples, comprising:

a first-pass velocity processing module, programmed to compute, for at least the first three harmonics of the patient'"'"'s heart rate, a first-pass harmonic phase velocity for each of said harmonic frequencies;

a first-pass pressure gradient processing module, programmed to computed, from said sequence of cuff pressure samples, a first-pass pressure gradient waveform;

a harmonic processing module, programmed to compute, for each of said at least first three harmonics, a frequency-domain modulus and phase of the first-pass pressure gradient waveform;

a first-pass flow processing module, programmed to compute, for each of said at least first three harmonics, a first-pass harmonic flow waveform from, at least in part, the corresponding frequency-domain modulus and phase of said first-pass pressure gradient waveform;

a visco-elastic shift processing module, programmed to compute, for each of said at least first three harmonics, a first-pass pressure-flow phase shift;

a second-pass velocity processing module, programmed to compute, for each of said at least first three harmonics, a second-pass estimate of harmonic phase velocity by correcting the corresponding first-pass harmonic phase velocity to account for the corresponding first-pass pressure-flow phase shift;

a final-pass pressure gradient processing module, programmed to compute a final-pass pressure gradient waveform from, at least in part, said second-pass harmonic phase velocities; and

,

a final-pass flow processing module, programmed to compute final-pass flow velocity waveform from, at least in part, said final-pass pressure gradient waveform.

81. A system, as defined in claim 80, wherein said first-pass velocity processing module includes:

means for computing a frequency-independent group propagation velocity; and

,

means for adjusting, for each harmonic, said frequency-independent group propagation velocity, using harmonic-dependent factors, to produce said first-pass estimate of harmonic phase velocity.

82. A system, as defined in claim 81, wherein said harmonic-dependent factors are non-linearly dependent on, at least, harmonic frequency, arterial radius and arterial elasticity.

83. A system, as defined in claim 82, wherein said harmonic-dependent factors include a Womersley modulus and Womersley phase factor, computed for each harmonic of interest.

84. A system, as defined in claim 80, wherein said harmonic processing module includes an FFT module.

85. A system, as defined in claim 80, wherein said harmonic processing module includes a DFT module.

86. A system, as defined in claim 80, wherein said first-pass pressure gradient processing module includes means for computing differences between successive cuff pressure samples.

87. A system, as defined in claim 86, wherein said first-pass pressure gradient processing module further includes means for multiplying said successive sample differences by a scaling factor related to the ratio of sampling rate to estimated propagation velocity.

88. A system, as defined in claim 80, wherein said first-pass flow processing module includes means for computing, for each harmonic, a sinusoidal waveform with frequency equal to the harmonic frequency, magnitude proportional, at least in part, to the corresponding harmonic pressure gradient modulus and phase offset, at least in part, by the corresponding harmonic pressure gradient phase.

89. A system, as defined in claim 88, wherein said first-pass flow processing module further includes means for scaling the magnitude of each sinusoidal waveform by a corresponding Womersley modulus and offsetting the phase of each sinusoidal waveform by a corresponding Womersley phase factor.

90. A system, as defined in claim 80, wherein said visco-elastic shift processing module includes:

means for computing, for each harmonic, a corresponding harmonic component of the cuff pressure sample waveform;

means for computing, for each harmonic, a plurality of incrementally phase-shifted flow-based elasticity waveforms; and

,

means for determining, for each harmonic, the first-pass pressure-flow phase shift by identifying the phase-shifted flow-based elasticity waveform whose peak corresponds most closely, in terms of phase, to the peak of the corresponding harmonic component of the cuff pressure sample waveform.

91. A system, as defined in claim 90, wherein said visco-elastic shift processing module further includes means for interpolating, for each harmonic, between the closest matching incrementally phase-shifted flow-based elasticity waveforms to determine said pressure-flow phase shift.

92. A system, as defined in claim 80, wherein said second-pass velocity processing module includes means for multiplying said first-pass phase velocity by factors related to the first-pass pressure-flow phase shift and the relative position of the pressure peak in the cuff pressure sample waveform.

93. A system, as defined in claim 80, wherein said final-pass pressure gradient processing module includes:

means for computing, for each harmonic, a series of harmonic cuff pressure waveform samples, differencing successive harmonic cuff pressure samples, and scaling said differences by a scaling factor related to the ratio of the sampling rate to the corresponding second-pass harmonic phase velocity, to determine a final-pass harmonic component of the final-pass pressure gradient waveform; and

,

means for summing the final-pass harmonic components to determine the final-pass pressure gradient waveform.

94. A system for non invasively monitoring blood pressure and flow in a patient, comprising:

an inflatable cuff, having predetermined inflation characteristics, wrapped around the patient'"'"'s upper arm or a leg;

an oscillometric control module, programmed to inflate the cuff to flow-occluding pressure, then monitor pressure pulsations over a series of successively lower inflation pressures;

a volumetric processing module, programmed to use the predetermined inflation characteristics to convert the monitored pressure pulsations into equivalent volumetric pulsations;

a vda envelope processing module, programmed to determine initial-flow and zero-stress cuff inflation pressures, from said volumetric pulsation data; and

,

an arterial calibration parameter processing module, programmed to determine parameters related to arterial wall thickness and radius, using, at least in part said initial-flow and zero-stress cuff inflation pressures.

95. A system, as defined in claim 94, further comprising:

a pressure servoing module, programmed to adjust the inflation pressure in the cuff to a monitoring pressure of approximately 10-25 mmHg; and

,

an arterial monitoring parameter processing module, programmed to determine arterial radius and elasticity at said monitoring pressure.

96. A system for continuously monitoring a plurality of hemodynamic parameters using a combination of time-domain and frequency-domain processing techniques, said system comprising:

a time-domain processing module programmed to compute, on a beat-by-beat basis, at least one time-domain parameter, selected from the list of;

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure.

a frequency-domain processing module, programmed to compute, on a beat-by-beat basis, at least one frequency-domain parameter, selected from the list of;

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag.

97. A system, as defined in claim 96, wherein said time-domain processing module also computes, on a beat-by-beat basis, at least one additional time-domain parameter, different from said at least one time-domain parameter, and selected from the list of:

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure.

98. A system, as defined in claim 96, wherein said time-domain processing module also computes, on a beat-by-beat basis, at least two additional time-domain parameters, different from said at least one time-domain parameter, and selected from the list of:

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure.

99. A system, as defined in claim 96, wherein said time-domain processing module also computes, on a beat-by-beat basis, at least three additional time-domain parameters, different from said at least one time-domain parameter, and selected from the list of:

volume displacement amplitude,

average external arterial radius,

radial distention,

incremental elasticity,

relative wall thickness,

pulse pressure,

pressure gradient,

diastolic pressure,

systolic pressure, and,

mean arterial pressure.

100. A system, as defined in claim 96, wherein said frequency-domain processing module also computes, on a beat-by-beat basis, at least one additional frequency-domain parameter, different from said at least one frequency-domain parameter, and selected from the list of:

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag.

101. A system, as defined in claim 97, wherein said frequency-domain processing module also computes, on a beat-by-beat basis, at least one additional frequency-domain parameter, different from said at least one frequency-domain parameter, and selected from the list of:

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag.

102. A system, as defined in claim 98, wherein said frequency-domain processing module also computes, on a beat-by-beat basis, at least one additional frequency-domain parameter, different from said at least one frequency-domain parameter, and selected from the list of:

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag.

103. A system, as defined in claim 99, wherein said frequency-domain processing module also computes, on a beat-by-beat basis, at least one additional frequency-domain parameter, different from said at least one frequency-domain parameter, and selected from the list of:

harmonic phase velocity,

harmonic pressure gradient,

harmonic flow velocity,

harmonic flow rate,

harmonic flow-based elasticity, and,

harmonic pressure-flow phase lag.

104. A system for continuous, noninvasive patient monitoring, comprising:

a cuff affixed to the upper arm or a leg of the patient;

a system calibration module; and

,

a beat-by-beat monitoring module, including;

means for providing a real-time blood pressure waveform; and

,

means for providing a real-time blood flow waveform computed, at least in part, in the frequency domain.

105. A system, as defined in claim 104, wherein said monitoring module further includes:

means for comparing parameters computed in the time and frequency domain to determine whether a system recalibration is needed; and

,

means for performing a system recalibration.

106. A system, as defined in claim 105, wherein the means for comparing compares parameters related to arterial elasticity.

107. A system, as defined in claim 104, wherein the means for providing a real-time blood pressure waveform operates in the time domain.

108. A system, as defined in claim 107, wherein the means for providing a real-time blood pressure signal corrects for visco-elastic pressure-flow phase lag, through use of a frequency domain-computed correction factor.

109. An article-of-manufacture, for use in connection with a computer-based method of continuous, noninvasive, hemodynamic monitoring, said article-of-manufacture comprising a computer-readable medium containing instructions which, when executed, cause said computer to:

receive a signal related to pressure pulsations in a patient'"'"'s artery; and

,

process said signal, at least in part in the frequency domain, to obtain pressure and flow waveforms, including a composite phase lag between peaks in the pressure and flow waveforms.

110. An article-of-manufacture, for use in connection with a computer-based method of estimating blood flow velocity, using a non invasive pressure cuff, said article-of-manufacture comprising a computer-readable medium containing instructions which, when executed, cause said computer to:

receive a pulsatile, pressure-related signal from said pressure cuff; and

,

compute, for each heartbeat cycle and each harmonic of interest, a first-pass estimate of harmonic phase velocity.

111. An article-of-manufacture, for use in connection with a computer-based method of estimating blood flow velocity, using a non invasive pressure cuff, said article-of-manufacture comprising a computer-readable medium containing instructions which, when executed, cause said computer to:

receive a pulsatile, pressure-related signal from said pressure cuff;

compute, at least in part from said pressure-related signal, a pressure gradient-related waveform, for each heartbeat cycle;

compute harmonic component(s) of said pressure gradient-related signal, for each harmonic of interest; and

,

compute an estimate of blood flow, for each harmonic of interest, from, at least in part, said computed harmonic component(s).

112. An article-of-manufacture, for use in connection with a computer-based method for noninvasively determining the longitudinal pressure gradient in a patient'"'"'s artery, said article-of-manufacture comprising a computer-readable medium containing instructions which, when executed, cause said computer to:

sample a pressure-related signal obtained from an externally-mounted pressure-sensitive device; and

,

compute said pressure gradient as a function, at least in part, of the difference between successive samples of said pressure-related signal.

113. An article-of-manufacture, for use in connection with a computer-based method for computing blood flow in a patient'"'"'s artery, from a sequence of cuff pressure samples, said article-of-manufacture comprising a computer-readable medium containing instructions which, when executed, cause said computer to:

compute, for at least the first three harmonics of the patient'"'"'s heart rate, a first-pass harmonic phase velocity for each of said harmonic frequencies;

compute, from said sequence of cuff pressure samples, a first-pass pressure gradient waveform;

compute, for each of said at least first three harmonics, a frequency-domain modulus and phase of the first-pass pressure gradient waveform;

compute, for each of said at least first three harmonics, a first-pass harmonic flow waveform from, at least in part, the corresponding frequency-domain modulus and phase of said first-pass pressure gradient waveform;

compute, for each of said at least first three harmonics, a first-pass pressure-flow phase shift;

compute, for each of said at least first three harmonics, a second-pass estimate of harmonic phase velocity by correcting the corresponding first-pass harmonic phase velocity to account for the corresponding first-pass pressure-flow phase shift;

compute a final-pass pressure gradient waveform from, at least in part, said second-pass harmonic phase velocities; and

,

compute a final-pass flow velocity waveform from, at least in part, said final-pass pressure gradient waveform.

114. An article-of-manufacture, for use in connection with a computer-based method of non invasively monitoring blood pressure and flow in a patient, using an inflatable cuff, having predetermined inflation characteristics, wrapped around the patient'"'"'s upper arm or a leg, said article-of-manufacture comprising a computer-readable medium containing instructions which, when executed, cause said computer to:

perform an oscillometric run by inflating the cuff to a flow-occluding pressure, then monitoring pressure pulsations over a series of successively lower inflation pressures;

use the predetermined inflation characteristics to convert the monitored pressure pulsations into equivalent volumetric pulsations;

determine initial-flow and zero-stress cuff inflation pressures; and

,

determine, at least in part from said initial-flow and zero-stress cuff inflation pressures, parameters related to arterial wall thickness and radius.

115. A noninvasive method for measuring physical parameters of an artery, comprising:

applying an inflatable cuff around the artery;

inflating the cuff to a pressure sufficient to substantially occlude blood flow through the artery;

deflating the cuff to ascertain a pressure, F, at which pulsations in said cuff first become detectable;

further deflating the cuff to ascertain a pressure, C, at which the rate-of-increase of pulsations in said cuff decreases with further cuff deflation; and

,

using F and C to determine a physical parameter of the artery.

116. A noninvasive method for measuring physical parameters of an artery, as defined in claim 115, wherein using F and C to determine a physical parameter of the artery includes using F and C to compute a relative wall thickness of the artery.

117. A noninvasive method for measuring physical parameters of an artery, as defined in claim 115, wherein using F and C to determine a physical parameter of the artery includes computing a relative wall thickness of the artery as a linear function of F and C.

118. A noninvasive method for measuring physical parameters of an artery, as defined in claim 116, further comprising:

using said relative wall thickness to determine an internal and external radius of said artery.

119. A noninvasive method for measuring physical parameters of an artery, as defined in claim 116, further comprising:

using said relative wall thickness and F and C pressures to determine a radius of the artery when the externally-applied cuff pressure is reduced such that the artery is not subjected to flow-occluding conditions and/or related hemodynamic disturbances that can cause significant measurement error.

120. A noninvasive method for measuring physical parameters of an artery, as defined in claim 119, further comprising:

using said radius without externally-applied cuff pressure and said relative wall thickness to compute a Young'"'"'s elasticity of said the artery wall.

121. A noninvasive method for measuring physical parameters of an artery, as defined in claim 115, but using a non-inflating band in place of the inflatable cuff.

122. A method for non invasively monitoring blood flow through an artery, comprising:

placing a band or cuff around a limb of a patient;

undertaking an initial calibration phase by controllably constricting and/or relaxing the band or cuff, while measuring pulsations from said artery;

computing, from measurements made during said calibration phase, a plurality of arterial parameters, including parameters related to the internal radius, external radius and elasticity of the artery;

adjusting the band or cuff to a reduced pressure or tension where it does not substantially constrict or deform the artery and undertaking a continuous flow monitoring phase by computing blood flow through the artery from pulsations measured with the band or cuff at said reduced pressure or tension.

123. A method for noninvasively monitoring blood flow through an artery, as defined in claim 122, wherein undertaking an initial calibration phase includes determining a cuff pressure or band tension at which arterial occlusion occurs.

124. A method for noninvasively monitoring blood flow through an artery, as defined in claim 123, wherein undertaking an initial calibration phase further includes determining a zero-stress cuff pressure or band tension.

125. A method for non invasively monitoring blood flow through an artery, as defined in claim 122, wherein undertaking a continuous flow monitoring phase includes:

computing a plurality of harmonic phase velocities;

computing a phase-corrected pressure gradient waveform; and

,

computing a flow velocity waveform.

126. A method for non invasively monitoring blood flow through an artery, as defined in claim 122, wherein undertaking a continuous flow monitoring phase includes performing at least one FFT or DFT computation per heartbeat.

127. A method for noninvasively monitoring blood flow through an artery, as defined in claim 122, wherein undertaking a continuous flow monitoring phase includes performing at least two FFT or DFT computations per heartbeat.

128. A method for noninvasively monitoring blood flow through an artery, as defined in claim 122, wherein undertaking a continuous flow monitoring phase further includes:

independently computing a selected parameter by both time-domain and frequency-domain methods;

computing difference(s) between value(s) of said selected parameter computed by said time-domain and frequency-domain methods; and

,

if said difference(s) indicate(s) a need to initiate a recalibration, then initiating a recalibration.

129. A method for non invasively monitoring blood flow through an artery, as defined in claim 122, wherein undertaking a continuous flow monitoring phase further includes use of a Womersley modulus and Womersley phase factor, computed or approximated for each harmonic of interest.

130. A method for non invasively monitoring blood flow through an artery, as defined in claim 128, wherein computing said selected parameter by a time-domain method includes computing a ratio of systolic to diastolic duration.

131. A method for computing a Young'"'"'s elasticity of an artery from noninvasive measurements, comprising:

determining a pulse pressure-related parameter from noninvasive measurements;

determining an arterial radius-related parameter from noninvasive measurements;

determining an arterial wall thickness-related parameter from noninvasive measurements;

determining a pulsatile radial displacement-related parameter from noninvasive measurements; and

using said pulse pressure-related, arterial radius-related, arterial wall thickness-related and pulsatile radial displacement-related parameters to compute a Young'"'"'s elasticity for said artery.

132. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 131, wherein said computation of said Young'"'"'s elasticity also utilizes a pressure-flow phase lag-related parameter.

133. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 132, wherein said pressure-flow phase lag-related parameter is estimated using an empirical time-domain relationship.

134. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 132, wherein said pressure-flow phase lag-related parameter is computed through a frequency-domain process.

135. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 132, wherein said pressure-flow phase lag-related parameter is computed using a pressure-flow shift normalization process.

136. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 131, further comprising:

using the computed Young'"'"'s elasticity and the wall thickness-related parameter to compute a wall-thickness compensated incremental elasticity that is applicable for large changes in artery radius.

137. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 136, further comprising:

refining said computation of wall-thickness compensated incremental elasticity using at least one empirical shift factor.

138. A method for computing a Young'"'"'s elasticity from noninvasive measurements, as defined in claim 136, further comprising:

refining said wall-thickness compensated incremental elasticity, using at least one empirical shift factor, to be consistent with initial OCD and continuous low-pressure cuff or band calibration measurements for the patient, thereby enabling continuous noninvasive monitoring in which blood pressures and elasticity values can be determined based on changes in artery radius values or other waveform contour parameters that exists with each heartbeat.

139. A method of computing blood flow in an artery, comprising:

using measurements received from a controllably restrictive band or cuff to determine a plurality of calibration parameters; and

,

using measurements received from an invasive pressure sensor, along with said plurality of calibration parameters, to compute blood flow in said artery.

140. A method of computing blood flow in an artery, as defined in claim 139, wherein said plurality of calibration parameters are computed, at least in part, from measurements taken during an OCD cycle.

141. A method of computing blood flow in an artery, as defined in claim 139, wherein using measurements received from an invasive pressure sensor, along with said plurality of calibration parameters, to compute blood flow includes computing a pressure gradient waveform.

142. A method of computing blood flow in an artery, as defined in claim 139, wherein using measurements received from an invasive pressure sensor, along with said plurality of calibration parameters, to compute blood flow includes performing a frequency-domain analysis of data received from said invasive pressure sensor.

143. A method for continuously and non invasively determining blood pressure, comprising:

determining a plurality of radius- and elasticity-related parameters through measurements taken during an OCD cycle; and

,

continuously determining blood pressure from non-occlusive measurements and said radius- and elasticity-related parameters.

144. A method for continuously and noninvasively determining blood pressure, as defined in claim 143, wherein continuously determining blood pressure from non-occlusive measurements and said radius- and elasticity-related parameters further includes:

utilizing at least one flow-related parameter, computed at least in part in the frequency domain from said non-occlusive measurements, to account for pressure-flow phase lag effect(s).

145. A method for continuously and non invasively determining blood pressure, as defined in claim 144, wherein said continuous blood pressure determination is performed at an elevated flow or non-resting state.

146. A noninvasive method for determining cardiac stroke volume, comprising:

utilizing a frequency-domain process to determine flow at an externally accessible arterial site; and

,

iteratively applying a flow-continuity analysis, or flow-resistance circuit concepts, to determine cardiac stroke volume.

147. A method, as defined in claim 146, further comprising:

determining cardiac output by multiplying said determined cardiac stroke volume by a measured heart rate.

148. A noninvasive system for determining cardiovascular parameters, comprising:

at least one sensor that generates a pulsatile signal based on pulsations in an artery;

at least one controllable flow-restrictive member that can be used to selectively limit blood flow through said artery;

said system further characterized in that it includes at least two characterizing features selected from the list of;

computation of both an internal radius and an external radius of said artery;

computation of an elasticity of said artery wall;

beat-by-beat computation of blood flow in said artery using a frequency-domain process;

beat-by-beat computation of blood pressure in said artery using at least one pressure-flow phase lag correction factor; and

,

beat-by-beat comparison of parameters computed in the frequency and time domains to determine whether system recalibration is needed.

149. A system, as defined in claim 148, wherein said system is further characterized in that it includes at least one additional characterizing feature selected from the list of:

computation of both an internal radius and an external radius of said artery;

computation of an elasticity of said artery wall;

beat-by-beat computation of blood flow in said artery using a frequency-domain process;

beat-by-beat computation of blood pressure in said artery using at least one pressure-flow phase lag correction factor; and

,

beat-by-beat comparison of parameters computed in the frequency and time domains to determine whether system recalibration is needed.

150. A method of non invasively determining cardiovascular parameters, comprising:

positioning at least two longitudinally separated sensors along an exterior conduit artery;

performing an OCD cycle to determine at least a parameter related to the internal radius of said conduit artery;

monitoring, at a low external applied pressure of approximately 10-25 mmHg, pressure pulsations received from said at least two longitudinally separated sensors; and

,

determining, from (i) said monitored pulsations, (ii) said at least a parameter related to the internal radius and (iii) the longitudinal separation between said at least two sensors, additional cardiovascular parameter(s).

151. A method of non invasively determining cardiovascular parameters, as defined in claim 150, wherein determining additional cardiovascular parameter(s) includes determining pulsatile propagation velocity.

152. A method of non invasively determining cardiovascular parameters, as defined in claim 151, wherein determining additional cardiovascular parameter(s) includes determining a Young'"'"'s elasticity from said propagation velocity.

153. A method of non invasively determining cardiovascular parameters, as defined in claim 150, wherein determining additional cardiovascular parameter(s) includes determining a pressure gradient waveform.

154. A method of non invasively determining cardiovascular parameters, as defined in claim 153, wherein determining additional cardiovascular parameter(s) includes determining a pressure gradient waveform by processing said monitored pulsations, at least in part, in the frequency domain.

155. A method of non invasively determining cardiovascular parameters, as defined in claim 153, wherein determining additional cardiovascular parameter(s) further includes computing a flow waveform.

156. A method of non invasively determining cardiovascular parameters, as defined in claim 150, wherein determining additional cardiovascular parameter(s) includes MAP.

157. A method of non invasively determining cardiovascular parameters, as defined in claim 156, wherein determining additional cardiovascular parameter(s) further includes determining systolic pressure.

158. A method of non invasively determining cardiovascular parameters, as defined in claim 156, wherein determining additional cardiovascular parameter(s) further includes determining diastolic pressure.

159. A noninvasive method for determining an oxygen perfusion parameter, comprising:

utilizing a frequency-domain or shadow monitoring waveform contour process to determine flow at an externally accessible arterial site; and

,

acquiring a hemoglobin oxygen saturation measurement, and

computing a product of said blood flow and said hemoglobin oxygen saturation measurement.

160. A method of non invasively determining an oxygen perfusion parameter, as defined in claim 159, wherein acquiring the oxygen saturation measurement involves use of a noninvasive pulse oximeter that measures oxygen saturation of blood hemoglobin using an infrared and red light emitting diode sensor or other generally equivalent sensor.

161. A method of noninvasively determining an oxygen perfusion parameter, as defined in claim 159, wherein the determination of oxygen perfusion also depends on other hemodynamic parameters indicative of greater or lesser than normal oxygen utilization as blood passes through tissue capillaries.

162. A method of non invasively determining an oxygen perfusion parameter, as defined in claim 159, wherein the determination of oxygen perfusion also depends on blood flow rates and respiratory variation of either or both of the cuff or the oximeter sensor, so as to enable identifying, distinguishing or quantifying greater or lesser than normal oxygen utilization as blood passes through tissue capillaries.

163. A method of non invasively determining a perfusion parameter, as defined in claim 159, wherein determining the perfusion parameter involves displaying parameter(s) related to the transport of nutrients in or blood components measured by biochemical sensing system(s).

164. A method for noninvasive determination of oxygen perfusion latency time comprising:

utilizing a frequency-domain or shadow monitoring waveform contour process to determine flow at an externally accessible arterial site;

obtaining a noninvasive measure of oxygen saturation at said externally accessible site;

computing an internal radius and mean flow velocity of said artery;

computing a latency parameter related to the total travel time of blood flow from the heart to the externally accessible arterial site.

165. A replaceable sensor assembly for use in connection with a non-invasive patient monitoring system, the sensor assembly including:

one or more sensor(s) capable of measuring or sensing conditions at the periphery of a patient'"'"'s body and generating signal(s) in response thereto;

an energy pathway capable of connecting the sensor(s) to the monitoring system; and

,

one or more non-volatile data storage elements capable of storing information indicative of the age, number of uses, and/or total hours of use of the replaceable sensor assembly.

166. A replaceable sensor assembly, as defined in claim 165, wherein the sensor assembly is adapted for use with a non-invasive blood pressure and/or flow monitoring system.

167. A replaceable sensor assembly, as defined in claim 166, wherein the one or more sensor(s) include at least one pressure sensor.

168. A replaceable sensor assembly, as defined in claim 167, wherein the sensor assembly further includes an inflatable cuff.

169. A replaceable sensor assembly, as defined in claim 165, wherein the energy pathway includes a tube capable of communicating pressure pulsations from the sensor assembly to the non-invasive monitoring system.

170. A replaceable sensor assembly, as defined in claim 169, wherein the energy pathway further includes one or more conductors or fiber-optic links.

171. A replaceable sensor assembly, as defined in claim 165, wherein the non-volatile storage elements comprise an EEPROM.

172. A replaceable sensor assembly, as defined in claim 171, wherein the information contained in the sensor assembly'"'"'s EEPROM is updated by the patient monitoring system each time the sensor assembly is used.

173. The replaceable sensor assembly, as defined in claim 165,, linked to a patient monitoring system that reads the non-volatile memory to determine if the cuff is needs to be replaced and, if so, warns the user of the system that he/she must replace the assembly.