Wavelet-based analysis of pulse oximetry signals

• US 20050070774A1
• Filed: 06/21/2002
• Published: 03/31/2005
• Est. Priority Date: 06/22/2001
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: CardioDigital Ltd.
• Inventors: Watson, James Nicholas, Addison, Paul Stanley
• Granted Patent: US 7,035,679 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6816 Ear lobe
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G06F 2218/00 Aspects of pattern recognition specially adapted for signal processing

Abstract

A pulse oximetry signal, suitably a photoplethysmogram (PPG), is decomposed by wavelet transform techniques, and the decomposed signal analysed to provide selected physiological data. The signal may be processed to remove noise, artefacts, or transient features. Information on respiration may also be recovered.

Claims

1. A method of measuring physiological parameters, comprising using a pulse oximeter to obtain a pulse oximetry signal, decomposing the pulse oximetry signal by wavelet transform analysis, and deriving one or more physiological parameters from the decomposed signal.

3. A method according to claim 1, in which the pulse oximetry signal is a photoplethysmogram (PPG).

4. A method as claimed in claim 1, including the steps of deriving the wavelet energy surfaces of the pulse oximeter signal, and plotting the surfaces against a location parameter and a scale parameter.

5. A method as claimed in claim 1, including the steps of deriving the wavelet transform modulus of the pulse oximeter signal, and plotting the modulus against a location parameter and a scale parameter.

6. A method as claimed in claim 4, in which the scale parameter is a characteristic frequency of the wavelet used in the decomposition.

7. A method as claimed in claim 4, in which the scale parameter is the wavelet dilation.

8. A method as claimed in claim 1, including visually displaying information derived from the pulse oximetry signal by the wavelet transform analysis.

9. A method as claimed in claim 8, in which said information is displayed in real time.

10. A method as claimed in claim 8, in which said information includes one or more of:

the distribution of energies within the pulse oximetry signal, coherent structures in the processed signal, a contour plot of the decomposed waveform, a surface plot of the decomposed waveform, and a 2D or 3D energy scalogram.

11. A method according to claim 8, in which the unprocessed pulse oximetry signal is also displayed.

12. A method according to claim 1, in which decomposing the pulse oximetry signal is effective to derive information relating to respiration.

13. A method according to claim 12, in which respiration information is derived from high amplitude ridges using ridge-following methods.

14. A method according to claim 12, in which the respiration information is derived by phase methods.

15. A method according to claim 14, in which the respiration information is derived by cross scale correlation of phase values.

16. A method according to claim 12, in which the respiration information is derived by analysis of amplitude or frequency modulation.

17. A method according to claim 1, in which decomposing the pulse oximetry signal is effective to remove, at least one of noise, artefact, and transient features.

18. A method according to claim 17, in which said removal employs inverse transformation of the cropped transform.

19. A method according to claim 17, in which said removal employs wavelet ridge methods.

20. A method according to claim 17, in which said removal employs modulus maxima methods.

21. A method according to claim 1, in which information from the transform is used to determine the present or predicted severity of illness of a subject.

24. A system according to claim 21, in which the signal processing means is arranged to process the pulse oximetry signal by the method of claim 3.

25. A system according to claim 21, further including a visual display unit operable to display the pulse oximetry signal and information derived therefrom in real time.

2. A method of processing a pulse oximetry signal, in which the pulse oximetry signal is decomposed by wavelet transform analysis.

22. A physiological measurement system comprising:

a pulse oximeter which includes an optical probe and circuit means connected to the probe to derive a pulse oximetry signal from a subject when the probe is applied to the subject, and signal processing means arranged to receive the pulse oximetry signal and to process the signal by wavelet transform techniques.

23. (canceled)