METHODS AND APPARATUS FOR MEASURING ARTERIAL COMPLIANCE, IMPROVING PRESSURE CALIBRATION, AND COMPUTING FLOW FROM PRESSURE DATA

• US 20040024324A1
• Filed: 08/01/2002
• Published: 02/05/2004
• Est. Priority Date: 08/01/2002
• Status: Active Grant

• Current Assignee: Hypertension Diagnostics, Inc.
• Original Assignee: Hypertension Diagnostics, Inc.
• Inventors: Bratteli, Christopher W.
• Granted Patent: US 6,733,461 B2
• 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 non-invasively measuring arterial compliance using the combination of noninvasive arterial tonometry and noninvasive cuff oscillometry. Some embodiments include an accurate calibration method using an oscillometric signal to calibrate the pressures of tonometric signals in a contralateral arterial site. The exact time at which two of the three oscillometric blood pressures (systolic pressure, mean pressure, diastolic pressure) are acquired are identified with precise locations on the un-calibrated tonometric pressure waveform. These two 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 osciilometric signal is acquired coincidentally with an un-calibrated 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. In some embodiments, a simple uncorrected volume arterial compliance curve is obtained by plotting relative arterial volume under the cuff against brachial arterial transmural pressure. The transmural pressure is the difference between cuff pressure and radial arterial pressure (adjusted for pressure head). Due to shear stresses at the ends of the cuff, this uncorrected volume arterial compliance curve overestimates the in vivo compliance for the arterial segment. Further embodiments account for this bias by providing a correction for the transmural pressure that is based on stress-strain properties of the upper arm.

Claims

1. A method for computerized calculation of a variable physiological parameter of a patient, the method comprising:

(a) identifying the physiological parameter to be quantitatively monitored and estimated;

(b) measuring an oscillometric signal and a tonometric physiological signal, which signals are quantitatively dependent on a particular value for the physiological parameter;

(c) obtaining a sequence of values that are based on the oscillometric signal and the tonometric signal;

(d) receiving the sequence of values as input signals to a computer system; and

(e) processing the input signals within the computer system to convert the sequence of values to an output signal corresponding to the particular value of the physiological parameter.

2. The method of claim 1, further comprising:

(f) using an oscillometric signal to calibrate tonometric pressure signals in a contralateral arterial site.

3. The method of claim 2, wherein a calibrated radial pressure waveform P_r(t) is derived from the tonometric signal S_r(t) as follows:

P_r(t)=(1/a_r)(S_r(t)−

b_r)+p

where a_r=(S_r(t_D)−

S_r(t_M))/(DBP−

MBP),

b_r=S_r(t_M)−

a_rMBP, and

p=gh are calibration factors, and where

=density of blood,

g=acceleration to gravity,

h=height difference between the oscillometric and the tonometric measurement sites, and is zero if the patient is supine,

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

DBP is oscillometric diastolic blood pressure measured near time t_D.

4. The method of claim 3, further comprising:

(g) calculating a first compliance value based on the calibrated radial pressure waveform;

(h) estimating end-effects of the oscillometric signal; and

(i) correcting the first compliance value using the estimated end effects.

5. The method of claim 1, wherein the processing function (e) includes estimating a first compliance value using a compliance pressure curve.

6. The method of claim 1, further comprising:

(j) using a tonometric signal to calibrate oscillometric pressure signals in a contralateral arterial site.

7. The method of claim 1, further comprising:

(k) estimating end-effects of oscillometric sensor apparatus on the oscillometric signal.

8. A method for computerized calculation of a variable physiological parameter of a patient, the method comprising:

(a) identifying the physiological parameter to be quantitatively monitored and estimated;

(b) coupling at least a first sensor and a second sensor to the patient, the first sensor and the second sensor each being responsive to monitor different time-varying physiological waveforms, which waveforms are quantitatively dependent on a particular value for the physiological parameter;

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

(d) receiving the sequence of digital values as input signals to a computer system; and

(e) processing the input signals within the computer system to convert the time-correlated dual sequence of digital values to an output signal corresponding to a value of the physiological parameter.

9. The method of claim 8, wherein the physiological parameter is vascular compliance, the first sensor monitors an oscillometric waveform, and the second sensor monitors a tonometric waveform.

10. The method of claim 8, wherein the physiological parameter is vascular compliance, the first sensor monitors an oscillometric waveform derived from oscillometric signals of a brachial artery site, and the second sensor monitors a tonometric waveform derived from tonometric signals of a contralateral radial artery site.

11. A system for computerized calculation of a variable physiological parameter of a patient, the system comprising:

a first sensor that measures an oscillometric physiological signal that is quantitatively dependent on a particular value for the physiological parameter;

a second sensor that measures a tonometric physiological signal that is quantitatively dependent on the particular value for the physiological parameter;

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

a second analog-to-digital converter, operatively coupled to the second sensor, that generates a second sequence of digital 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 to generate an output signal corresponding to the particular value of the physiological parameter.

12. The system of claim 11, 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.

13. The system of claim 12, wherein a calibrated radial pressure waveform P_r(t) is derived from the tonometric signal S_r(t) as follows:

P_r(t)=(1/a_r)(S_r(t)−

b_r)+p

where a_r=(S_r(t_D)−

S_r(t_M))/(DBP−

MBP),

b_r=S_r(t_M)−

a_rMBP, and

p=gh are calibration factors, and where

=density of blood,

g=acceleration to gravity,

h=height difference between the oscillometric and the tonometric measurement sites, and is zero if the patient is supine,

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

DBP is oscillometric diastolic blood pressure measured near time t_D.

14. The system of claim 13, wherein the computer system further 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 using the estimated end effects.

15. The system of claim 11, wherein the computer system further estimates a first compliance value using a compliance pressure curve.

16. The system of claim 11, wherein the computer system further uses a tonometric signal to calibrate oscillometric pressure signals in a contralateral arterial site.

17. The system of claim 11, wherein the computer system further estimates end-effects of oscillometric sensor apparatus on the oscillometric signal.

18. A system for computerized calculation of a variable physiological 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.

19. The system of claim 18, 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 physiological parameter.