METHOD OF MEASURING AN ARTEFACT REMOVED PHOTOPLETHYSMOGRAPHIC (PPG) SIGNAL AND A MEASUREMENT SYSTEM

• US 20140058272A1
• Filed: 03/26/2012
• Published: 02/27/2014
• Est. Priority Date: 03/25/2011
• Status: Active Grant

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Naing, Nyan Myo, Samsudin, Mohamad Sulhede Bin, Thaveeprungsriporn, Visit, MD Kassim, Md Irwan Bin
• Granted Patent: US 9,326,731 B2
• Time in Patent Office: Days
• US Class Current: 600/479
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

A method of measuring an artefact removed photoplethysmographic (PPG) signal and a measurement system for measuring an artefact removed photoplethysmographic (PPG) signal are provided. The method comprises obtaining a first set of PPG signals from a plurality of detectors at respective measurement sites using a first illumination; obtaining a second set of PPG signals from the plurality of detectors using a second illumination; obtaining at least two pairs of PPG signals, each pair comprising one PPG signal from the first set and one PPG signal from the second set, and for each pair, computing an artefact reference signal to obtain a candidate PPG signal; and choosing one of the candidate PPG signals as the artefact removed PPG signal.

Claims

1. A method of measuring an artefact removed photoplethysmographic (PPG) signal, the method comprising,

obtaining a first set of PPG signals from a plurality of detectors at respective measurement sites using a first illumination;

obtaining a second set of PPG signals from the plurality of detectors using a second illumination;

obtaining at least two pairs of PPG signals, each pair comprising one PPG signal from the first set and one PPG signal from the second set, and for each pair, computing an artefact reference signal to obtain a candidate PPG signal; and

choosing one of the candidate PPG signals as the artefact removed PPG

2. The method as claimed in claim 1, wherein the step of computing an artefact reference signal comprises using a vector subspace approach whereby, for the pairs of PPG signals, artefact reference signals between

3. The method as claimed in claim 2, wherein the considered artefact reference signals are separated into a plurality of subspaces, further wherein from each of said plurality of subspaces, a selected artefact reference signal is applied to a filter with one of said one PPG signal from the first set and one PPG signal from the second set to determine a subspace for analysis.

4. The method as claimed in claim 3, wherein the step of choosing one of the candidate PPG signals comprises using one or more parameters to compare the candidate PPG signals.

5. The method as claimed in claim 4, wherein the parameters comprise an averaged standard deviation of maximum peak points and minimum peak points of each candidate PPG signal.

6. The method as claimed in claim 4, wherein the parameters comprise a cross-correlation of two separated segments of each candidate PPG signal.

7. The method as claimed in claim 1, further comprising applying a force at the plurality of detectors such that signal amplitudes of the first set of PPG signals and/or the second set of PPG signals are maximum.

8. The method as claimed in claim 7, comprising computing an area under curve measurement using waveforms of the PPG signals to determine whether the signal amplitudes are maximum.

9. The method as claimed in claim 8, wherein the computing an area under curve measurement comprises sampling each waveform and filtering each sample, further wherein the area under curve measurement is a summation of absolute values of the filtered samples.

10. The method as claimed in claim 1, further comprising providing the first and second illumination using a light emitting diode.

11. The method as claimed in claim 10, wherein the light emitting diode is positioned such that motion artefacts are minimized in the first set of PPG signals and/or the second set of PPG signals.

12. The method as claimed in claim 1, wherein the first illumination is red light and the second illumination is infrared red light.

27. A computer readable data storage medium having stored thereon computer code means for instructing a processor of a measurement system for measuring an artefact removed photoplethysmographic (PPG) signal to execute a method of measuring an artefact removed PPG signal as claimed in claim 1.

13. A measurement system for measuring an artefact removed photoplethysmographic (PPG) signal, the system comprising,

a measurement device comprising a plurality of detectors at respective measurement sites for obtaining a first set of PPG signals using a first illumination and for obtaining a second set of PPG signals using a second illumination;

a computation unit for obtaining at least two pairs of PPG signals, each pair comprising one PPG signal from the first set and one PPG signal from the second set, and the computation unit being capable of, for each pair, computing an artefact reference signal to obtain a candidate PPG signal; and

the computation unit being capable of choosing one of the candidate PPG signals as the artefact removed PPG signal.

14. The system as claimed in claim 13, wherein for computing an artefact reference signal, the computation unit is capable of using a vector subspace approach whereby, for the pairs of PPG signals, artefact reference signals between

15. The system as claimed in claim 14, wherein for the vector subspace approach, the computation unit separates the considered artefact reference signals into a plurality of subspaces, and from each of said plurality of subspaces, the computation unit selects a selected artefact reference signal and applies the selected artefact reference signal to a filter with one of said one PPG signal from the first set and one PPG signal from the second set to determine a subspace for analysis.

16. The system as claimed in claim 15, wherein for choosing one of the candidate PPG signals, the computation unit is capable of using one or more parameters to compare the candidate PPG signals.

17. The system as claimed in claim 16, wherein the parameters comprise an averaged standard deviation of maximum peak points and minimum peak points of each candidate PPG signal.

18. The system as claimed in claim 16, wherein the parameters comprise a cross-correlation of two separated segments of each candidate PPG signal.

19. The system as claimed in claim 13, further comprising a force application means for applying a force at the plurality of detectors such that signal amplitudes of the first set of PPG signals and/or the second set of PPG signals are maximum.

20. The system as claimed in claim 19, wherein the computation unit is capable of computing an area under curve measurement using waveforms of the PPG signals to determine whether the signal amplitudes are maximum.

21. The system as claimed in claim 20, wherein for the computing an area under curve measurement, the computation unit samples each waveform and filters each sample, and further the computation unit computes the area under curve measurement as a summation of absolute values of the filtered samples.

22. The system as claimed in claim 19, further comprising an automatic sizing component to automatically size the measurement device for application to a subject, the automatic sizing component functioning as the force application means.

23. The system as claimed in claim 13, further comprising a light emitting diode for providing the first and second illumination.

24. The system as claimed in claim 23, wherein the light emitting diode is positioned such that motion artefacts are minimized in the first set of PPG signals and/or the second set of PPG signals.

25. The system as claimed in claim 13, wherein the first illumination is red light and the second illumination is infrared red light.

26. The system as claimed in claim 13, wherein the measurement device and the computation unit each comprise a wireless transceiver to facilitate communication using a wireless communication protocol.