Adaptive Frequency Domain Filtering for Improved Non-Invasive Blood Pressure Estimation

• US 20090209868A1
• Filed: 02/20/2008
• Published: 08/20/2009
• Est. Priority Date: 02/20/2008
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hersh, Lawrence T., Donehoo, Robert F., Kolluri, Sai
• Granted Patent: US 8,556,821 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• 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 for processing oscillometric data from a plurality of pressure steps to determine the blood pressure of a patient as disclosed herein. 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. A harmonic frequency calculator is connected to the heart rate monitor and derives at least the heart rate fundamental frequency. A filter connected to the time to frequency domain converter and the harmonic frequency calculator that produces a filter frequency domain oscillometric signal. A reconstruction calculator receives the filtered frequency domain oscillometric signal and reconstructs a time domain oscillometric signal. A method of computing an oscillometric envelope for use in determining the blood pressure of a patient is also disclosed herein.

Claims

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

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

receiving an indication of the heart rate of the patient;

computing the fundamental frequency of the heart rate;

computing at least one harmonic frequency of the heart rate;

converting the oscillometric signal to the frequency domain;

filtering the frequency domain oscillometric signal using a band pass filter comprising the fundamental frequency of the heart rate to produce a first filtered frequency domain signal;

filtering the frequency domain oscillometric signal using a band pass filter comprising the at least one harmonic frequency of the heart rate to produce a second filtered frequency domain signal;

reconstructing the oscillometric signal from the first and second filtered frequency domain signals to produce a reconstructed oscillometric signal;

computing an oscillometric envelope data point from the reconstructed oscillometric signal.

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, wherein the step of computing at least one harmonic frequency of the heart rate includes computing the first harmonic frequency and the second harmonic frequency.

4. The method of claim 3, further comprising the step of filtering the frequency domain oscillometric signal with a pass band centered at the first harmonic frequency to produce a second filtered frequency domain signal;

and

filtering the frequency domain oscillometric signal with a pass band centered at the second harmonic frequency to produce a third filtered frequency domain signal.

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

comparing the heart rate of the patient to a predetermined threshold; and

if the heart rate of the patient is below the predetermined threshold, filtering the frequency domain oscillometric signal with a single band pass filter that comprises the fundamental frequency and the at least one harmonic frequency.

6. The method of claim 1 wherein the steps of filtering the frequency domain oscillometric signal are performed using a reasonably narrow band pass filter centered at the fundamental frequency of the heart rate and at least one narrow band pass filter centered at least one harmonic frequency.

7. The method of claim 1, wherein the received oscillometric signal is from a single pressure step of the blood pressure cuff signal.

8. The method of claim 6, further comprising repeating the method at a plurality of blood pressure cuff pressure steps to produce a plurality of computed envelope data points.

9. The method of claim 8, further comprising:

computing an oscillometric envelope from the computed envelope data points; and

determining the mean arterial pressure, the systolic pressure, and the diastolic pressure from the oscillometric envelope.

10. The method of claim 6, wherein the step of computing an oscillometric envelope data point further includes removing the first and last reconstructed oscillations and determining an oscillometric envelope data point from the remaining reconstructed oscillations.

11. 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 a patient;

receiving an indication of the heart rate of the patient;

computing the fundamental frequency of the heart rate;

computing at least one harmonic frequency of the heart rate;

converting the oscillometric signal to the frequency domain;

filtering the frequency domain oscillometric signal with at least one band pass filter comprising the fundamental frequency of the heart rate and the at least one harmonic frequency of the heart rate; and

reconstructing the oscillometric signal from the filtered frequency domain signal to produce a reconstructed oscillometric signal.

12. The method of claim 11 wherein the step of filtering the frequency domain oscillometric signal further comprises filtering the frequency domain oscillometric signal with separate pass bands centered at the fundamental frequency and the at least one harmonic frequency.

13. The method of claim 12 wherein the pass bands centered at the fundamental frequency and the at least one harmonic frequency are narrow.

14. The method of claim 11 further comprising:

computing an oscillometric envelope data point from the reconstructed oscillometric signal;

repeating the method at a plurality of blood pressure cuff pressure steps to produce a plurality of computed envelope data points;

computing an oscillometric envelope from the computed envelope data points; and

determining the mean arterial pressure, the systolic pressure, and the diastolic pressure from the oscillometric envelope.

15. The method of claim 11 further comprising processing the oscillometric data to remove a DC portion of the oscillometric data.

16. A system for processing an oscillometric signal from a plurality of pressure steps of a blood pressure cuff to determine the blood pressure of a patient, the system comprising:

a heart rate monitor connected to the patient, the heart rate monitor acquiring the patient'"'"'s heart rate at each pressure step;

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 the heart rate fundamental frequency;

a filter connected to the time-to-frequency domain converter and the harmonic frequency calculator, the filter comprising at least the fundamental frequency, the filter producing a filtered frequency domain oscillometric signal;

a reconstruction calculator that receives the filtered frequency domain oscillometric signal and reconstructs a time domain oscillometric signal from the filtered frequency domain oscillometric signal;

an oscillometric envelope calculator that processes the time domain oscillometric signal at each pressure step to produce an oscillometric envelope from envelope data points corresponding to each pressure step; and

a blood pressure determination calculator connected to the oscillometric envelope calculator, the blood pressure determination calculator analyzes the oscillometric envelope to determine the blood pressure of the patient.

17. The system of claim 16 wherein the harmonic frequency calculator further derives at least the heart rate first and second harmonic frequencies, and the filter further comprises the first and second harmonic frequencies.

18. The system of claim 17 wherein the filter further comprises pass bands centered at the heart rate fundamental frequency and at least the first and second harmonic frequencies.

19. The system of claim 18 wherein the pass bands centered at the heart rate fundamental frequency and at least the first and second harmonic frequencies are of a bandwidth less than the fundamental frequency.

20. The system of claim 16 further comprising a DC removal calculator, the calculator receiving the oscillometric data and removing the DC component from the oscillometric data.