Method and apparatus for calibrating and measuring arterial compliance and stroke volume

• US 20040167413A1
• Filed: 02/17/2004
• Published: 08/26/2004
• Est. Priority Date: 08/01/2002
• Status: Abandoned Application

• Current Assignee: Hypertension Diagnostics, Inc.
• Original Assignee: Hypertension Diagnostics, Inc.
• Inventors: Bratteli, Christopher W.
• Application Number:
  US10/780,960
• Publication Number:
  US 20040167413A1
• Time in Patent Office: Days
• US Class Current: 600/490
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: Y10S 128/92 Computer assisted medical diagnostics

Abstract

Methods and apparatus for measuring arterial compliance using combined noninvasive arterial tonometry and cuff oscillometry. Some embodiments include a calibration method using an oscillometric signal to calibrate the pressures of tonometric signals in a contralateral arterial site. The times at which two of the three oscillometric blood pressures (systolic pressure, mean pressure, diastolic pressure) are acquired are identified with times of uncalibrated tonometric pressure waveform. These blood pressures are then used to calibrate the tonometric pressure waveform along (optionally) with adjustments for head pressure. For example, a left brachial arterial cuff oscillometric signal is acquired coincidentally with an uncalibrated right radial arterial pressure tonometric signal. The time points of mean arterial pressure and diastolic pressure are determined from the oscillometric signal and identified with coinciding time points on the tonometric signal to produce a calibration. All pressures are then adjusted by the head pressure between the brachial and radial sites.

Claims

21. A system for computerized calculation of one or more vascular-compliance parameters of a patient, the system comprising:

a first sensor that measures an oscillometric arterial signal;

a second sensor that measures a tonometric arterial signal;

a first analog-to-digital converter, operatively coupled to the first sensor, that generates a sequence of oscillometric values that are based on the oscillometric signal;

a second analog-to-digital converter, operatively coupled to the second sensor, that generates a sequence of tonometric values that are based on the tonometric signal;

a computer system, operatively coupled to the first and second analog-to-digital converters, wherein the computer system processes the first and second sequences of values and calibrates the sequence of tonometric values based on the one or more oscillometric parameters to generate one or more values each corresponding to one of the one or more vascular-compliance parameters.

22. The system of claim 21, wherein the computer system processes the sequence of tonometric values S_r(t) to generate a calibrated tonometric pressure waveform P_r(t) as follows:

P_r(t)=((S_r(t)+additive correction_r)*multiplicative correction_r)

wherein the additive correction_r and the multiplicative correction_r are calibration constants based at least in part on blood pressure parameters derived from the oscillometric signal, and S_r(t) is the tonometric signal value at time t.

23. The system of claim 22, wherein the computer system calculates:

the multiplicative correction_r=(DBP−

MBP)/(S_r(t_D)−

S_r(t_M)), and the additive correction_r=a_rMBP−

S_r(t_M), wherein

MBP is oscillometric mean arterial blood pressure measured near time t_M, and

DBP is oscillometric diastolic blood pressure measured near time t_D.

24. The system of claim 22, wherein the computer system calculates:

the multiplicative correction_r=(SBP−

MBP)/(S_r(t_S)−

S_r(t_M)), and the additive correction_r=a_rMBP−

S_r(t_M), wherein

MBP is oscillometric mean arterial blood pressure measured near time t_M, and

SBP is oscillometric systolic blood pressure measured near time t_S.

25. The system of claim 22, wherein the computer system calculates:

the multiplicative correction_r=(SBP−

DBP)/(S_r(t_S)−

S_r(t_D)), and the additive correction_r=a_rDBP−

S_r(t_D), wherein

SBP is oscillometric systolic blood pressure measured near time t_S, and

DBP is oscillometric diastolic blood pressure measured near time t_D.

26. The system of claim 21, wherein the computer system processes the sequence of tonometric values S_r(t) to generate a calibrated tonometric pressure waveform P_r(t) as follows:

P_r(t)=((S_r(t)−

b_r)(1/a_r))+p

where a_r and b_r are calibration constants based at least in part on blood pressure parameters derived from the oscillometric signal, and p is a hydrostatic pressure head parameter constant.

27. The system of claim 26, wherein the computer system calculates:

a_r=(S_r(t_D)−

S_r(t_M))/(DBP−

MBP), and b_r=S_r(t_M)−

a_rMBP, wherein

MBP is oscillometric mean arterial blood pressure measured near time t_M, and

DBP is oscillometric diastolic blood pressure measured near time t_D.

28. The system of claim 26, wherein the computer system calculates:

a_r=(S_r(t_s)−

S_r(t_M))/(SBP−

MBP), and b_r=S_r(t_M)−

a_rMBP), wherein

MBP is oscillometric mean arterial blood pressure measured near time t_M, and

SBP is oscillometric systolic blood pressure measured near time t_S.

29. The system of claim 26, wherein the computer system calculates:

a_r=(S_r(t_S)−

S_r(t_D))/(SBP−

DBP), and

b_r=S_r(t_D)−

a_rDBP, wherein SBP is oscillometric systolic blood pressure measured near time t_S, and

DBP is oscillometric diastolic blood pressure measured near time t_D.

30. The system of claim 21, wherein the computer system uses a mean blood pressure value and a diastolic blood pressure value from the oscillometric signal to calibrate the sequence of tonometric pressure values.

31. The system of claim 21, wherein the computer system uses a mean blood pressure value and a systolic blood pressure value from the oscillometric signal to calibrate the sequence of tonometric pressure values.

32. The system of claim 21, wherein the computer system uses a systolic blood pressure value and a diastolic blood pressure value from the oscillometric signal to calibrate the sequence of tonometric pressure values.

33. The system of claim 21, wherein the computer system calculates a first compliance value based on the calibrated radial pressure waveform, estimates end-effects of the oscillometric signal;

and corrects the first compliance value based on the estimated end effects.

34. The system of claim 21, wherein the computer system generates a first compliance value from a compliance pressure curve.

35. The system of claim 22, wherein the computer system:

uses time points t_M and t_S from the sequence of values based on the tonometric signal, and locates corresponding tonometric signal values shifted to the nearest peak (for t_S), nadir (for t_D), and calibrating using the formula

P_r(t)=((S_r(t)+additive correction_r)*multiplicative correction_r),

uses tonometric and oscillometric pressures, P and P_c, to compute transmural pressure P_TR=P−

P_c at each time point,

uses P_c and n_c to compute V_c, and

numerically differentiates the data pairs (−

V_c, P_TR) to obtain

$C=\frac{<br><br>V}{<br><br>P_{\mathrm{TR}}}=-\frac{<br><br>V_c}{<br><br>P_{\mathrm{TR}}}$

as a function of P_TR.

36. The system of claim 35, wherein the computer system plots C(P_TR) and reporting C(SBP), C(DBP), C(120), C(80), and pressure at C_max.

37. The system of claim 35, wherein the computer system calculates a mean compliance as follows:

38. The system of claim 21, wherein the first sensor senses the oscillometric signal from one side of a patient, the second sensor senses the tonometric signal from a contralateral arterial site, and the computer uses the oscillometric signal to calibrate tonometric pressure signals in the contralateral arterial site.

39. The system of claim 21, wherein the computer system further estimates end-effects of oscillometric sensor apparatus on the oscillometric signal.

40. The method of claim 21, wherein the computer system further uses a tonometric signal to calibrate oscillometric pressure signals in a contralateral arterial site.

41. A system for computerized calculation of a vascular compliance parameter of a patient, the system comprising:

a first sensor that measures an oscillometric signal of the patient;

a second sensor that measures a tonometric signal of the patient;

means for calibrating the tonometric signal based on the oscillometric signal and for calculating a value for the vascular-compliance parameter.

42. The system of claim 41, wherein the means for calibrating further includes:

means for obtaining a time-correlated dual sequence of digital values that are based on the waveforms monitored by the first and second sensors; and

means for processing the input signals to convert the time-correlated dual sequence of digital values to an output signal corresponding to a value of the vascular-compliance parameter.