Method and apparatus for the noninvasive determination of arterial blood pressure

• US 6,471,655 B1
• Filed: 06/29/1999
• Issued: 10/29/2002
• Est. Priority Date: 06/29/1999
• Status: Expired due to Term

• Current Assignee: Tensys Medical Inc. (Recorders & Medicare Systems Pvt Ltd.)
• Original Assignee: Vitalwave Corporation (Recorders & Medicare Systems Pvt Ltd.)
• Inventors: Baura, Gail D.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/342,549
• Time in Patent Office: 1,218 Days
• Field of Search: 600/481, 600/485, 600/490, 600/493-496, 600/500, 600/504
• US Class Current: 600/485
• 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 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/489 Blood vessels
• CPC Class Codes: A61B 5/6806 Gloves
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 8/04 Measuring blood pressure
• CPC Class Codes: A61B 8/4227 characterised by straps, belts, cuffs or braces

Abstract

A method and apparatus for determining the mean arterial blood pressure (MAP) of a subject during tonometric conditions. In one embodiment, the apparatus comprises one or more pressure and ultrasound transducers placed over the radial artery of a human subject'"'"'s wrist, the latter transmitting and receiving acoustic energy so as to permit the measurement of blood velocity during periods of variable compression of the artery. During compression, the ultrasound velocity waveforms are recorded and processed using time-frequency analysis. The time at which the mean time-frequency distribution is maximal corresponds to the time at which the transmural pressure equals zero, and the mean pressure read by the transducer equals the mean pressure within the artery. In another aspect of the invention, the ultrasound transducer is used to position the transducer over the artery such that the accuracy of the measurement is maximized. In yet another aspect of the invention, a wrist brace useful for measuring blood pressure using the aforementioned apparatus is disclosed.

Claims

1. A method of measuring blood pressure within a blood vessel of a subject, comprising:

compressing at least a portion of said blood vessel to a varying degree as a function of time;

transmitting an acoustic wave into said blood vessel during said compressing;

receiving an echo of said acoustic wave from said blood vessel during said compressing;

estimating at least one parameter based on said echo; and

determining the pressure within said blood vessel when said parameter is estimated to satisfy a predetermined condition.

2. The method of claim 1, further comprising:

measuring the frequency of said echo; and

calculating the velocity of blood flowing within said blood vessel as a function of the measured frequency.

3. The method of claim 2, wherein the act of estimating at least one parameter comprises estimating the diameter of said blood vessel.

4. The method of claim 1, wherein the act of compressing comprises compressing the radial artery of human being.

5. The method of claim 1, further comprising:

selecting at least one time interval; and

calculating a mean distribution value during said at least one time interval.

6. The method of claim 5, herein said time-frequency distribution comprises a pseudo-Wigner distribution.

7. The method of claim 1, herein said predetermined condition comprises a maximized time-frequency distribution.

8. The method of claim 1, further comprising varying the position of transducers which transmit said acoustic wave and receive said echo, respectively, in relation to said blood vessel and based on said echo.

9. The method of claim 8, wherein the act of varying the position comprises varying the transverse position of transducers which transmit said acoustic wave and receive said echo, respectively, in relation to said blood vessel and based at least in part on the amplitude of said echo.

10. A method of measuring blood pressure, comprising:

positioning a first transducer capable of producing a first signal related to the pressure applied thereto, in proximity to the blood vessel of a subject;

urging said first transducer against the tissue of said subject, said first transducer at least partly compressing said blood vessel in response to said urging;

positioning a second transducer capable or transmitting and receiving acoustic energy in proximity to said blood vessel;

transmitting an acoustic wave into said blood vessel using said second transducer;

receiving at least one echo from said blood vessel using said second transducer, said second transducer generating a second signal related to said echo;

measuring the frequency of said echo based on said second signal;

forming a time-frequency distribution based on said frequency; and

measuring the pressure within said blood vessel using said first transducer when said time-frequency distribution is maximized.

11. A method of measuring blood pressure within a blood vessel of a subject, comprising:

progressively varying the compression of at least a portion of said blood vessel;

transmitting acoustic energy into said blood vessel during at least a portion of said act of varying the compression;

receiving echoes of said acoustic energy from said blood vessel during at least a portion of said act of varying the compression;

forming a time-frequency representation of said echoes; and

determining the pressure within said blood vessel when said representation satisfies a given condition.

12. The method of claim 11, wherein said act of progressively varying the compression comprises:

compressing said blood vessel to a substantially occluded state; and

reducing the level of compression of said blood vessel thereafter.

13. The method of claim 11, wherein said act of transmitting comprises:

positioning a transducer element substantially adjacent said blood vessel and in contact with the skin superior thereto; and

transmitting ultrasonic waves into said blood vessel.

14. The method of claim 11, wherein said act of forming a time-frequency representation comprises forming a time frequency distribution, and said act of determining comprises determining the pressure when said time-frequency distribution is substantially maximized.

15. The method of claim 14, wherein said time frequency distribution comprises a Wigner distribution.

16. The method of claim 14, further comprising:

selecting at least one time interval; and

calculating a mean value of said distribution during said at least one time interval.

17. The method of claim 11, wherein said time frequency representation comprises a Wigner distribution.

18. The method of claim 11, further comprising:

selecting at least one time interval; and

calculating a mean value of said representation during said at least one time interval.

19. The method of claim 11, further comprising varying the position of the source of said acoustic energy with respect to said blood vessel based at least in part on said received echoes.

20. The method of claim 19, wherein said act of varying the position comprises varying the position based at least in part on the amplitude of said echoes.

21. The method of claim 11, wherein said act of varying the compression comprises compressing a portion of said blood vessel using a surface of a tonometric pressure transducer.

22. The method of claim 11, wherein said act of forming a time-frequency representation comprises determining the mean time-frequency distribution at zero (0) Hz.

23. The method of claim 11, wherein said act of forming a time-frequency representation comprises:

determining the blood velocity;

forming a time-frequency distribution based at least in part on said blood velocity;

and

calculating the mean distribution value for each cardiac beat of said subject.

24. A method of measuring blood pressure within a blood vessel of a subject, comprising the steps of:

progressively varying the compression of at least a portion of said blood vessel to alter the hemodynamic properties thereof;

transmitting acoustic energy into said blood vessel during at least a portion of said act of varying the compression to generate echoes form said vessel and blood contained therein;

receiving said echoes of said acoustic energy from said blood vessel during at least a portion of said act of varying the compression;

forming a time-frequency representation of said echoes to identify at least one predetermined condition therein; and

determining when said representation satisfies said predetermined condition to determine the pressure within said blood vessel non-invasively.

25. A method of measuring blood pressure within the radial artery of a living subject, comprising:

varying the level of compression of at least a portion of said artery;

transmitting ultrasonic energy into said artery during at least a portion of said act of varying the compression;

receiving echoes of said acoustic energy from said artery during at least a portion of said act of varying the compression;

determining blood velocity based at least in part on said echoes;

forming a time-frequency distribution of said echoes based at least in part on said blood velocity;

selecting an interval within which said distribution is evaluated;

determining the mean of said distribution within said interval; and

determining the pressure within said artery when said mean of said distribution satisfies a given condition.

26. A blood pressure monitoring device, comprising:

first apparatus adapted to compress a blood vessel of a subject and measure the pressure applied thereto;

second apparatus adapted to transmit acoustic energy into said blood vessel and receive at least one echo resulting therefrom; and

a processor operatively coupled to said first and second apparatus and configured to process said measured pressure and said at least one echo;

wherein said device is further configured to;

(i) progressively vary the compression of at least a portion of said blood vessel;

(ii) transmit said acoustic energy into said blood vessel and receive said at least one echo therefrom during at least a portion of said act of varying the compression;

(iii) form a time-frequency representation of said at least one echo using at least said processor; and

(iv) determine the pressure within said blood vessel when said representation satisfies a given condition.