USE OF THE FREQUENCY SPECTRUM OF ARTIFACT IN OSCILLOMETRY

• US 20110237962A1
• Filed: 03/23/2010
• Published: 09/29/2011
• Est. Priority Date: 03/23/2010
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hersh, Lawrence T., Kolluri, Sai
• Granted Patent: US 8,740,803 B2
• Time in Patent Office: Days
• US Class Current: 600/493
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

A system and method for processing oscillometric data from a plurality of pressure steps to determine the blood pressure of a patient. A heart rate monitor connected to the patient acquires the patient'"'"'s heart rate. A time-to-frequency domain converter receives oscillometric data and converts the oscillometric data into the frequency domain. Based upon the calculated heart rate, the system and method filters the frequency domain oscillometric signal with pass bands centered at the fundamental frequency and at least one fundamental frequency. The energy of the frequency domain signal within the pass bands is compared to at least a portion of the energy of the frequency domain oscillometric signal outside of the pass bands. Based upon the comparison, the signal determines whether the signal at the current pressure step should be utilized in calculating the blood pressure of the patient.

Claims

1. A method of computing an oscillometric envelope for use in determining the blood pressure of a patient, the method comprising the steps of:

receiving an oscillometric signal from a blood pressure cuff positioned on the patient;

receiving an indication of the heart rate of the patient;

computing a fundamental frequency of the heart rate;

converting the oscillometric signal to the frequency domain;

filtering the frequency domain oscillometric signal using a band pass filter having a first pass band centered around the fundamental frequency;

calculating the energy of the frequency domain oscillometric signal in the first pass band centered around the fundamental frequency;

calculating the energy of the frequency domain oscillometric signal in at least a portion of the signal outside of the first pass band;

calculating a ratio of the energy of the frequency domain oscillometric signal outside the first pass band to the energy of the frequency domain oscillometric signal within the first pass band;

reconstructing the oscillometric signal from the filtered frequency domain signal in the first pass band only when the calculated ratio is below a threshold; and

computing an oscillometric envelope data point from the reconstructed oscillometric signal only when the calculated ratio is below the threshold.

2. The method of claim 1 wherein the step of converting the oscillometric signal to the frequency domain is performed using a fast Fourier transform (FFT).

3. The method of claim 1 further comprising the steps of:

computing at least a first harmonic frequency of the heart rate;

filtering the frequency domain oscillometric signal using a second band pass filter having a second pass band centered around the first harmonic frequency;

calculating the energy of the frequency domain oscillometric signal in the second pass band;

combining the calculated energy within the second pass band with the calculated energy within the first pass band; and

calculating the ratio based upon the combined energy.

4. The method of claim 1 wherein the step of calculating the energy outside of the first pass band comprises:

calculating the energy of the frequency domain oscillometric signal in a first noise band having a first frequency range below the first pass band;

calculating the energy of the frequency domain oscillometric signal in a second noise band having a second frequency range above the first pass band; and

combining the calculated energy in the first and second noise bands to define the energy outside of the first pass band.

5. The method of claim 4 wherein the first and second frequency ranges are less than the fundamental frequency.

6. The method of claim 1 further comprising the steps of:

computing at least a first harmonic frequency of the heart rate;

filtering the frequency domain oscillometric signal using a second band pass filter having a second pass band centered around the first harmonic frequency;

calculating the energy of the frequency domain oscillometric signal in the second pass band centered around the first harmonic frequency;

calculating the energy of the frequency domain oscillometric signal in a third noise band below the second pass band and a fourth noise band above the second pass band;

calculating a second ratio of the energy in the second pass band to the energy in the combination of the third and fourth pass bands; and

reconstructing the oscillometric signal from the filter frequency domain signal using only the first or second pass band if the first or second pass bands have a ratio below the threshold.

7. The method of claim 1 wherein the received oscillometric signal is from a single pressure step for the blood pressure cuff and the computed data point is at the single pressure step.

8. The method of claim 7 further comprising the step of repeating the method at a plurality of blood pressure cuff pressure steps to compute a plurality of envelope data points.

9. The method of claim 8 further comprising the steps of:

obtaining additional oscillometric signals at each of the pressure steps when the calculated ratio exceeds the threshold; and

reducing the pressure of the blood pressure cuff to the next pressure step when the calculated ratio is below the threshold.

10. A method of processing oscillometric data for use in determining the blood pressure of a patient, the method comprising:

receiving an oscillometric signal from a blood pressure cuff connected to the patient;

receiving an indication of the heart rate of the patient;

computing a fundamental frequency and at least one harmonic frequency of the heart rate;

converting the oscillometric signal to the frequency domain;

filtering the frequency domain signal with separate pass bands centered at the fundamental frequency and the at least one harmonic frequency;

determining the energy of the frequency domain oscillometric signal in the pass bands;

determining the energy of the frequency domain oscillometric signal in at least portions of the signal other than the pass bands;

calculating a ratio of the energy of the frequency domain oscillometric signal outside the pass bands to the energy of the frequency domain oscillometric signal within the pass bands;

reconstructing the oscillation signal from the filtered frequency domain signal in the pass bands when the calculated ratio is below a threshold; and

computing an oscillometric envelope data point for the current pressure within the blood pressure cuff based upon the reconstructed oscillometric signal.

11. The method of claim 10 wherein the step of converting the oscillometric signal to the frequency domain is performed using a fast Fourier transform (FFT).

12. The method of claim 10 wherein the oscillometric signal is received at a pressure step, further comprising the steps of:

obtaining additional oscillometric signals at the pressure step when the calculated ratio exceeds the threshold; and

reducing the pressure of the blood pressure cuff to a subsequent pressure step when the calculated ratio is below the threshold.

13. The method of claim 10 wherein the frequency domain oscillometric signal is filtered at least at a first harmonic frequency and a second harmonic frequency.

14. The method of claim 13 further comprising the steps of:

determining the energy of the frequency domain oscillometric signal in a noise band above the pass band and below the pass band for the fundamental frequency and each of the harmonic frequencies;

comparing the energy in the noise bands above and below the pass bands to the energy within the pass bands; and

disregarding the energy in each pass band when the energy in the noise band exceeds a threshold relative to the energy in the pass band.

15. The method of claim 10 further comprising the step of presenting a quality indicator that is based on the energy in the pass band relative to the energy outside of the pass band.

16. The method of claim 15 wherein the quality indicator is a visual indicator.

17. A system for processing oscillometric data for use in determining the blood pressure of a patient, the system comprising:

a heart rate monitor connected to the patient, the heart rate monitor acquiring the patient heart rate;

a blood pressure cuff positioned on the patient and deflatable in a series of pressure steps;

a time-to-frequency domain converter that receives the oscillometric signal acquired at each pressure step and converts the oscillometric data into the frequency domain;

a harmonic frequency calculator connected to the heart rate monitor, the harmonic frequency calculator deriving at least a heart rate fundamental frequency and at least one harmonic frequency;

a first filter having a first pass band centered around the fundamental frequency;

a second filter having a second pass band centered around the at least one harmonic frequency;

a controller for calculating a ratio of the energy of the frequency domain signal outside each of the first and second pass bands to the energy of at least a portion of the frequency domain oscillometric signal within the first and second pass bands; and

a blood pressure determination calculator that determines an oscillometric envelope data point when the calculator ratio is below a threshold.

18. The system of claim 17 further comprising at least one filter having a noise band located adjacent to one of the first and second pass bands.

19. The system of claim 17 wherein the pass bands centered at the heart rate fundamental frequency and at least one of the first harmonic frequencies each have a band width less than the fundamental frequency.

20. The system of claim 17 wherein the pressure within the blood pressure cuff is decreased when the ratio is less than the threshold.