Method for estimating a central pressure waveform obtained with a blood pressure cuff

• US 9,414,755 B2
• Filed: 05/13/2009
• Issued: 08/16/2016
• Est. Priority Date: 05/15/2008
• Status: Active Grant

• Current Assignee: Uscom Ltd.
• Original Assignee: Uscom Ltd.
• Inventors: Lowe, Andrew
• Primary Examiner(s): Kahelin, Michael
• Assistant Examiner(s): TRAN, THO Q
• Application Number:
  US12/454,123
• Publication Number:
  US 20090287097A1
• Time in Patent Office: 2,652 Days
• Field of Search: 600490-494
• US Class Current: 1/1
• CPC Class Codes: A61B 5/02108 from analysis of pulse wave characteristics
• 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: A61B 5/411 Detecting or monitoring allergy or intolerance reactions to an allergenic agent or substance
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: G07F 17/26 for printing, stamping, franking, typing or teleprinting apparatus ticket printing or the like apparatus G07F17/42

Abstract

A physics-based mathematical model is used to estimate central pressure waveforms from measurements of a brachial pressure waveform measured using a supra-systolic cuff. The method has been tested in numerous subjects undergoing cardiac catheterisation. Central pressure agreement was within 11 mm Hg and as good as the published non-invasive blood pressure agreement between the oscillometric device in use and the so-called “gold standard.” It also exceeds international standards for the performance of non-invasive blood pressure measurement devices. The method has a number of advantages including simplicity of application, fast calculation and accuracy of prediction. Additionally, model parameters have physical meaning and can therefore be tuned to individual subjects. Accurate estimation of central waveforms also allow continuous measurement (with intermittent calibration) using other non-invasive sensing systems including photoplethysmography.

Claims

1. A method of sensing and analyzing supra-systolic blood pressure waveforms obtained non-invasively from a brachial artery in an arm of a patient, using a blood pressure cuff and cuff pressure transducer, to estimate central artery blood pressures, said method comprising the steps of:

(a) applying and inflating a blood pressure cuff on the patient'"'"'s arm to a supra-systolic pressure;

(b) using a non-invasive sensor, sensing a succession supra-systolic cuff pressure waveforms associated with the brachial artery in said patient'"'"'s arm, each supra-systolic cuff pressure waveform forming a heart-pulse synchronous cuff pressure signal representing at least one cardiac ejection cycle;

(c) using a computer, analyzing the supra-systolic cuff pressure waveforms using a first mathematical model relating the heart-pulse synchronous cuff pressure signal and brachial pressure near the cuff on said patient'"'"'s arm to produce an estimated brachial pressure signal representing estimated brachial pressure waveforms, wherein the heart-pulse synchronous cuff pressure signal is scaled relative to previously measured systolic and diastolic pressures, such that the amplitude of the estimated brachial pressure signal is a proportion of a difference between the previously measured systolic and diastolic pressures;

(d) using a computer, analyzing the estimated brachial pressure waveforms using a second mathematical model relating the estimated brachial pressure signal and a central pressure at the root of the brachial artery to produce estimated central artery blood pressures and estimated central artery blood pressure waveforms, whereby the second mathematical model includes at least one parameter with physical meaning selected from a group consisting of (a) an impedance relationship at the cuff and (b) a parameter relating a phase of a pressure wave at substantially the subclavian root to a phase of a supra-systolic pressure wave at the occluding cuff; and

(e) generating a computer output representing estimated central artery blood pressures based on the analysis.

2. The method according to claim 1, wherein the systolic and diastolic blood pressures are measured using the blood pressure cuff on said patient'"'"'s arm before, during or after the measurement of said supra-systolic cuff pressure waveforms.

3. The method according to claim 1, further comprising a correction step such that estimated brachial pressures between maximum and minimum estimated brachial pressures are corrected by a non-linear function, with said non-linear function monotonically increasing from the min to the maximum estimated brachial pressures, but being proportionally greater for pressures between the maximum and minimum estimated brachial pressure.

4. The method according to claim 1, wherein, according to the second mathematical model relating the estimated brachial pressure signal and central pressure at the root of the brachial artery, the estimated central artery blood pressure is a sum of a first proportion of the estimated brachial pressure signal shifted forwards in time by a propagation time, and a second proportion of the estimated brachial pressure signal shifted backwards in time by the propagation time, whereby the first proportion is a ratio of reflection coefficient at the cuff to the reflection coefficient plus one, and the second proportion is the ratio of one to the reflection coefficient plus one.

5. The method according to claim 3, wherein the correction step is of a form such that the corrected pressure estimate, if scaled between zero and one, equals a ratio of (a) a control variable minus one plus an uncorrected pressure scaled between zero and one to (b) the control variable plus one plus the uncorrected pressure scaled between zero and one, whereby the control variable controls an amount of non-linear correction.

6. The method according to claim 4, wherein the reflection coefficient at the cuff is assumed to be a predetermined constant.

7. The method according to claim 4, wherein the reflection coefficient at the cuff is determined based on an estimated change in artery cross section as a result of the application of a supra-systolic pressure to the blood pressure cuff.

8. The method according to claim 7, wherein the determination of the reflection coefficient depends upon a predetermined relationship between an estimated unoccluded artery size, the supra-systolic cuff sure and the previously measured systolic and diastolic pressures.

9. The method according to claim 4, wherein the propagation time is assumed to be a predetermined constant.

10. The method according to claim 4, wherein the propagation time is determined by an estimate of artery length and pulse wave speed made using a predetermined relationship with respect to at least one parameter of a patient, selected from the group consisting of gender, age, height, upper arm circumference, and brachial Augmentation Index.

11. The method according to claim 4, further comprising the step of measuring the propagation time in the brachial artery.

12. The method according to claim. 11, wherein the propagation time is the difference in time between an occurrence of a foot. of the estimated brachial pressure pulse and an occurrence of a preceding R-wave of a synchronously collected ECG signal.

13. The method according to claim 11, wherein the propagation time is the difference in time between an occurrence of an foot of the estimated brachial pressure pulse and an occurrence of an foot of a simultaneously collected carotid tonometric signal.

14. The method according to claim 11, wherein propagation time is a difference in time between an occurrence of a dichrotic notch in the estimated brachial pressure pulse and a time of a heart sound corresponding to closure of an aortic valve simultaneously collected from a heart sound sensor.

15. The method according to claim 1, wherein the output of the analysis is a central systolic blood pressure.

16. The method according to claim 1, wherein the output of the analysis is a central diastolic blood pressure.

17. The method according to claim 1, wherein the output of the analysis central pulse pressure.

18. The method according to claim 1, wherein the output of the analysis is central Augmentation Index.

19. The method according to claim 1, wherein the output of the analysis is the maximum rate of change of central pressure with time.

20. The method according to claim 1, wherein the output of the analysis is central systolic ejection period.

21. The method according to claim 1, wherein the impedance relationship at the cuff is a reflection coefficient.

22. The method according to claim 1, wherein the impedance relationship at the cuff is a frequency response function.

23. The method according to claim 1, wherein the impedance relationship at the cuff is a digital filter.

24. The method according to claim 1., wherein the parameter relating the phase of the pressure wave at substantially the subclavian root the phase the supra-systolic pressure wave at the occluding cuff is a propagation time.

25. The method according to claim 1, wherein the parameter relating the phase of the pressure wave at substantially the subclavian root to the phase of the supra-systolic pressure wave at the occluding cuff is a frequency response function.

26. The method according to claim 1, wherein the parameter relating the phase of the pressure wave at substantially the subclavian root to the phase of the supra-systolic pressure wave at the occluding cuff is a digital filter.

27. A method analyzing central blood pressure waveforms obtained non-invasively from a brachial artery in an arm of a patient, using a blood pressure cuff and cuff pressure transducer as a first non-invasive sensor and as a second non-invasive sensor of heart synchronous pulse signals, thereby to estimate central artery blood pressures, said method comprising the steps of

(a) applying and inflating a blood pressure cuff on the patient'"'"'s arm to a supra-systolic pressure;

(b) sensing a first succession of supra-systolic cuff pressure waveforms associated with the brachial artery in said patient'"'"'s arm using the first non-invasive sensor, each supra-systolic cuff pressure waveform forming a heart-pulse synchronous cuff pressure signal representing at least one cardiac ejection cycle;

(c) using a computer, analyzing the supra-systolic cuff pressure waveforms using a first mathematical model relating the heart-pulse synchronous cuff pressure signal and brachial pressure near the cuff on said patient'"'"'s arm to produce an estimated brachial pressure signal representing estimated brachial pressure waveforms;

(d) using a computer, analyzing the estimated brachial pressure waveforms using a second mathematical model relating the estimated brachial pressure signal and a central pressure at the root of the brachial artery to produce estimated central artery blood pressures and estimated central artery blood pressure waveforms, whereby the second mathematical model includes at least one parameter with physical meaning selected from a group consisting of (a) an impedance relationship at the cuff and (b) a parameter relating a phase of the pressure wave at substantially the subclavian root to a phase of a supra-systolic pressure wave at the occluding cuff;

(e) sensing a second succession of heart-pulse synchronous cuff pressure signals using the second non-invasive sensor approximately corresponding in time to the first succession of supra-systolic cuff pressure waveforms;

(f) using a computer, calculating a mathematical relationship relating the estimated central artery blood pressures to the second succession of heart-pulse synchronous cuff pressure signals;

(g) deflating the blood pressure cuff to a sub-diastolic pressure;

(h) sensing a third succession of heart-pulse synchronous cuff pressure signals using the second non-invasive sensor;

(i) using a computer, determining the central artery blood pressures by using the previously calculated mathematical relationship relating the estimated central artery blood pressures to the second succession of heart-pulse synchronous cuff pressure signals and to the third succession of heart-pulse synchronous cuff pressure signals from the second non-invasive sensor; and

(j) generating a computer output representing estimated central artery blood pressures based on the analysis.

28. The method according to claim 27, wherein the second non-invasive sensor of heart-pluse synchronous cuff pressure is a photoplethysmograph sensor.

29. The method according to claim 27, wherein the second noninvasive sensor of heart synchronous pulse signals is a tonometric sensor.

30. The method according to claim 27, wherein the second non-invasive sensor of heart synchronous pulse signals is a blood pressure cuff applied to another limb of the patient.

31. The method according to claim 27, wherein the mathematical relationship relating the estimated central artery pressures to the second succession of pulse signals is that of a transfer function.

32. The method according to claim 27, wherein the mathematical relationship relating the estimated central artery pressures to the second succession of heart-pulse synchronous cuff pressure signals is that of a digital filter.

33. The method according to claim 27, further comprising the step of comparing a difference between the third succession of heart-pulse synchronous cuff pressure signals from the second non-invasive sensor and the second succession of heart-pulse synchronous cuff pressure signals the second non-invasive sensor against predetermined criteria, and, if the difference should meet said predetermined criteria, performing another measurement according to the method of claim 27 to recalibrate the relationship between the second non-invasive sensor signal and the estimated central blood pressure.