Method and apparatus for automatic non-invasive monitoring of a patient's blood pressure

• US 5,427,109 A
• Filed: 03/09/1994
• Issued: 06/27/1995
• Est. Priority Date: 01/19/1993
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Frankenreiter, Michael
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US08/208,448
• Time in Patent Office: 475 Days
• Field of Search: 128/677-683, 364/413.03
• US Class Current: 600/493
• 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 5/7257 using Fourier transforms

Abstract

In a method for automatic non-invasive monitoring of a patient'"'"'s blood pressure a cuff is applied around an arm of the patient and inflated to a predetermined pressure, whereafter the pressure in said cuff is stepwise reduced and the applied pressure is held constant at each step until at least one oscillation caused by a heartbeat has occurred. In such a method, the systolic and/or diastolic and/or mean blood pressure are determined on the basis of the relations of the amplitudes or peak values of the oscillations at the various pressure steps. In order to avoid errors in the blood pressure determination due to artifacts, a first aspect of the invention provides for a spectral analyzer for pressure signal frequencies between 6 and 10 Hz. When this analyzer detects spectral signal components of the pressure signal in the pressure channel above a specific amplitude limit, the instantaneous oscillation is rejected. According to a second aspect of the invention, the gradient and the scatter of the pressure channel signal are examined within a time window, and, in case one of the two limit values for said ascent or scattering are exceeded, a movement artifact is detected.

Claims

1. A method for use in automatic non-invasive monitoring of a patient'"'"'s blood pressure, wherein a cuff around an arm of the patient is inflated to a preselectd pressure so as to generate a pressure signal from an attached pressure sensor, the method comprising the steps of:

stepwise reducing a pressure applied to said cuff,

holding the applied pressure constant at each step until

at least one oscillation caused by a heartbeat has occurred in said pressure signal, or until

a preselectd time period has expired,

selecting at least one spectral component value of said at least one oscillation of the pressure signal in a frequency range between 6 and 10 Hz;

examining whether an amplitude of said selected spectral component value of said at least one oscillation in the frequency range between 6 and 10 Hz exceeds a limit value, and

if the limit is exceeded, disregarding said at least one oscillation of the pressure signal in further processing of said signal;

or

if the limit is not exceeded, processing said at least one oscillation for use in determining a blood pressure parameter.

2. A method according to claim 1, wherein the determining step determines the spectral component of said at least one oscillation of the pressure signal in the frequency range between 6 and 10 Hz upon receiving a pressure channel signal produced by said pressure sensor, said pressure channel signal containing both oscillation components add constant components.

3. A method according to claim 2, further including deriving signals for use in determining a blood pressure parameter on the basis of an oscillation channel signal obtained by band-pass filtering of the pressure channel signal.

4. A method according to claim 2, further including deriving signals for use in determining a blood pressure parameter by employing an oscillation channel signal obtained by subtracting a mean value of the pressure channel signal from the pressure channel signal.

5. A method according to claim 1, wherein the selecting step performs a discrete Fourier transform to select the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz.

6. A method according to claim 1, wherein the selecting step performs a Fast Fourier transform to select the at least one spectral component of the pressure signal in the frequency range between 6 and 10 Hz.

7. A method according to claim 2, wherein the selecting step selects the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz, by observing a time window of the pressure channel with a duration between 0.2 and 5 seconds, and performing a discrete Fourier transform for plural frequencies between 6 and 10 Hz upon a signal resulting from a pressure channel signal after subtraction of a constant component.

8. A method for use in automatic non-invasive monitoring of a patient'"'"'s blood pressure, wherein a cuff is applied around an arm of the patient, the cuff is inflated so as to generate a pressure signal from an attached pressure sensor, the method comprising the steps of:

stepwise inflating said cuff to a preselectd pressure and holding an applied pressure constant at each step until

at least one oscillation caused by a heartbeat has occurred in said pressure signal, or until

a preselectd time period has expired,

selecting at least one spectral component value of said at least one oscillation of said pressure signal in the frequency range between 6 and 10 Hz,

examining whether the amplitude of said selected spectral component of said at least one oscillation in the frequency range between 6 and 10 Hz exceeds a limit value, and

if the limit value is exceeded, disregarding the at least one oscillation of the pressure signal in further processing of said signal;

or

if the limit value is not exceeded, processing the at least one oscillation for use in determining a blood pressure parameter,

after having reached the preselectd pressure, deflating said cuff.

9. A method according to claim 8, wherein the determining step selects the spectral component of the pressure signal in the frequency range between 6 and 10 Hz by employing a pressure channel signal produced by a pressure sensor, said pressure channel signal containing, in addition to oscillation components, also constant components.

10. A method according to claim 8, wherein the blood pressure parameter is one of systolic or diastolic or mean blood pressure and performing processing of the pressure signal by employing an oscillation channel signal obtained by band-pass filtering of the pressure channel signal or by subtracting the mean value of the pressure channel signal from the pressure channel signal.

11. A method according to claim 8, wherein the blood pressure parameter is one of systolic or diastolic or mean blood pressure and performing processing of the pressure signal by employing an oscillation channel signal obtained by subtracting the mean value of the pressure channel signal from the pressure channel signal.

12. A method according to claim 8, wherein the selecting step performs a discrete Fourier transform to select the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz.

13. A method according to claim 8, wherein the selecting step performs a fast Fourier transform to select the at least one spectral component of the pressure signal in the frequency range between 6 and 10 Hz.

14. A method according to claim 8, wherein the selecting step selects the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz, by observing a time window of the pressure channel with a duration between 0.2 and 5 seconds, and performing a discrete Fourier transform for several frequencies between 6 and 10 Hz upon a signal resulting from a pressure channel signal by subtraction of a constant component.

15. A method for use in automatic non-invasive monitoring of a patient'"'"'s blood pressure, wherein a cuff is applied around an arm of the patient, the cuff is continuously inflated to a preselectd pressure or continuously deflated from a preselectd pressure so as to generate a pressure signal from an attached pressure sensor, the method comprising the steps of:

selecting at least one spectral component value of an oscillation of the pressure signal in the frequency range between 6 and 10 Hz,

examining whether an amplitude of the spectral component value exceeds a limit value, and

if the limit is exceeded, disregarding the oscillation of the pressure signal in further processing of said signal;

or

if the limit is not exceeded, processing the oscillation for use in determining a blood pressure parameter.

16. A method according to claim 15, wherein the determining step determines the spectral component of the oscillation of the pressure signal in the frequency range between 6 and 10 Hz by employing a pressure channel signal containing both oscillation components and constant components.

17. A method according to claim 15, wherein the blood pressure parameter is one of systolic or diastolic or mean blood pressure and performing processing of the pressure signal by employing an oscillation channel signal obtained by band-pass filtering of a pressure channel signal or by subtracting the mean value of the pressure channel signal from the pressure channel signal.

18. A method according to claim 15, wherein the blood pressure parameter is one of systolic or diastolic or mean blood pressure and performing processing of the pressure signal by employing an oscillation channel signal obtained by subtracting the mean value of a pressure channel signal from the pressure channel signal.

19. A method according to claim 15, wherein the selecting step performs a discrete Fourier transform to select the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz.

20. A method according to claim 15, wherein the selecting step performs a Fast Fourier transform to select the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz.

21. A method according to claim 15, wherein the selecting step selects the at least one spectral component value of the pressure signal in the frequency range between 6 and 10 Hz, by observing a time window of the pressure channel with a duration between 0.2 and 5 seconds, and performing a discrete Fourier transform for several frequencies between 6 and 10 Hz upon a signal resulting from a pressure channel signal by subtraction of a constant component.

22. A blood pressure measuring apparatus for use in automatic noninvasive monitoring of a patient'"'"'s blood pressure, said apparatus comprising:

a cuff for application to an arm of a patient;

a pump means for inflating said cuff to a preselectd pressure;

a pressure sensor coupled to said cuff for producing a pressure signal,

valve means coupled to said cuff for stepwise reducing a pressure applied to said cuff and for holding an applied pressure constant at each step until

at least one oscillation caused by a heartbeat has occurred in a pressure signal, or until

a preselectd period of time has expired;

spectral component selecting means for selecting at least one spectral component value of the pressure signal in the 6 and 10 Hz frequency range;

processor means for examining whether an amplitude of the spectral component value exceeds a limit value, and

if yes, disregarding an oscillation of the pressure signal;

or

if no, processing the oscillation for selecting either a systolic or a diastolic or a mean blood pressure.

23. A blood pressure measuring apparatus for use in automatic noninvasive monitoring of a patient'"'"'s blood pressure, said apparatus comprising:

a cuff for application to an arm of the patient,

a pressure sensor for producing a pressure signal,

a pump means for stepwise inflating said cuff to a predetermined pressure and for holding an applied pressure constant at each step during inflation until

at least one oscillation caused by a heartbeat has occurred in a pressure signal, or until

a predetermined period of time has expired,

a spectral component selecting means for determining at least one spectral component value of the pressure signal in a frequency range between 6 and 10 Hz,

processor means for examining whether an amplitude of the spectral component value exceeds a limit value, and

if yes, disregarding an oscillation of the pressure signal;

or

if no, processing the oscillation for determining a blood pressure parameter,

valve means for deflating said cuff when a pressure applied to the cuff has reached the predetermined pressure.

24. A blood pressure measuring apparatus for use in automatic noninvasive monitoring of a patient'"'"'s blood pressure, said apparatus comprising:

a cuff for application to an arm of the patient,

pump means for continuously inflating said cuff to a predetermined pressure,

a pressure sensor for producing a pressure signal during a course of continuously inflating said cuff to said predetermined pressure,

a spectral component selecting means for determining at least one spectral component value of the pressure signal in a frequency range between 6 and 10 Hz,

processor means for examining whether an amplitude of the spectral component value exceeds a limit value, and

if yes, disregarding an oscillation including said one spectral component value of the pressure signal;

or

if no, processing the oscillation for selecting a blood pressure parameter, and

valve means for deflating said cuff when a pressure applied to the cuff has reached the predetermined pressure.

25. A blood pressure measuring apparatus for use in automatic noninvasive monitoring of a patient'"'"'s blood pressure, said apparatus comprising:

a cuff for application to an arm of the patient,

pump means for inflating said cuff to a predetermined pressure,

valve means for continuously deflating said cuff from said predetermined pressure,

a pressure sensor for producing a pressure signal during a course of continuously deflating said cuff from said predetermined pressure,

a spectral component selecting means for determining at least one spectral component value of the pressure signal in a frequency range between 6 and 10 Hz,

processor means for examining whether an amplitude of the spectral component value exceeds a limit value, and

if yes, disregarding an oscillation including said one spectral component value of the pressure signal;

or

if no, processing the oscillation for determining a blood pressure parameter.