Signal processing systems and methods using multiple signals

• US 9,031,627 B2
• Filed: 10/01/2008
• Issued: 05/12/2015
• Est. Priority Date: 07/15/2008
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul Stanley, Watson, James Nicholas
• Primary Examiner(s): Szmal, Brian
• Assistant Examiner(s): Nguyen, Huong Q.
• Application Number:
  US12/242,918
• Publication Number:
  US 20100014723A1
• Time in Patent Office: 2,414 Days
• Field of Search: 600/310, 600/323, 600/324, 600/326, 600/331, 600/336
• US Class Current: 600/310
• 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 5/726 using Wavelet transforms

Abstract

According to embodiments, techniques for signal processing using multiple signals are disclosed. A first scalogram may be generated from a first signal and a second scalogram may be generated from a second signal. A modified or masked scalogram may then be generated based on the first and second scalograms. The modified scalogram may then be used to determine at least one physiological parameter. In some embodiments, one or both of the first signal and the second signal may be photoplethysmograph (PPG) signals obtained from a pulse oximeter.

Claims

1. A method for determining a physiological parameter, comprising:

receiving a first signal corresponding to a first wavelength of light and a second signal corresponding to a second wavelength of light;

performing a continuous wavelet transform on the first signal and the second signal to produce a first transformed signal and a second transformed signal;

generating a first scalogram based at least in part on the first transformed signal;

generating a second scalogram based at least in part on the second transformed signal;

generating a scalogram mask based at least in part on the first scalogram and based at least in part on the second scalogram;

filtering one of the first scalogram and the second scalogram using at least the scalogram mask to produce a filtered scalogram; and

determining a physiological parameter based at least in part on the filtered scalogram.

2. The method of claim 1, wherein generating the scalogram mask comprises summing the first scalogram and the second scalogram.

3. The method of claim 1, wherein generating the scalogram mask comprises subtracting the first scalogram from the second scalogram.

4. The method of claim 1, wherein generating the scalogram mask comprises applying a scaling factor to either the first scalogram or the second scalogram before summing or subtracting the first and second scalograms.

5. The method of claim 1, wherein the first signal and/or the second signal is a photoplethysmograph (PPG) signal.

6. The method of claim 1, wherein generating a scalogram mask comprises determining regions where one of the first scalogram and the second scalogram exceed a threshold value.

7. The method of claim 1 further comprising generating a plurality of additional filtered scalograms based at least in part on a plurality of different scaling factors.

8. The method of claim 7 further comprising:

computing a summation of each of the filtered scalogram and the plurality of additional filtered scalograms; and

generating a Time-Scale Metric (TSM) plot of the summations plotted against the summations'"'"' respective scaling factors.

9. The method of claim 1 wherein determining a physiological parameter comprises determining the physiological parameter in the time-scale domain.

10. The method of claim 1 wherein determining a physiological parameter comprises performing an inverse wavelet transform of the filtered scalogram and determining the physiological parameter in the time domain.

11. A system for determining a physiological parameter, comprising:

a sensor capable of generating a first signal corresponding to a first wavelength of light and a second signal corresponding to a second wavelength of light; and

a processor capable of;

performing a continuous wavelet transform on the first signal and the second signal to produce a first transformed signal and a second transformed signal;

generating a first scalogram based at least in part on the first transformed signal;

generating a second scalogram based at least in part on the second transformed signal;

generating a scalogram mask based at least in part on the first scalogram and based at least in part on the second scalogram;

filtering one of the first scalogram and the second scalogram using at least the scalogram mask to produce a filtered scalogram; and

determining a physiological parameter based at least in part on the filtered scalogram.

12. The system of claim 11, wherein the processor is capable of summing the first scalogram and the second scalogram.

13. The system of claim 11, wherein the processor is capable of subtracting the first scalogram from the second scalogram.

14. The system of claim 11, wherein the processor is capable of applying a scaling factor to either the first scalogram or the second scalogram before summing or subtracting the first and second scalograms.

15. The system of claim 11, wherein at least one of the first signal and the second signal is a photoplethysmograph (PPG) signal.

16. The system of claim 11, wherein the processor is capable of determining regions where one of the first scalogram and the second scalogram exceeds a threshold value.

17. The system of claim 11 wherein the processor is capable of generating a plurality of additional filtered scalograms based at least in part on a plurality of different scaling factors.

18. The system of claim 17 wherein the processor is capable of:

computing a summation of each of the filtered scalogram and the plurality of additional filtered scalograms; and

generating a Time-Scale Metric (TSM) plot of the summations plotted against the summations'"'"' respective scaling factors.

19. The system of claim 11 wherein the processor is capable of determining the physiological parameter in the time-scale domain.

20. The system of claim 11 wherein the processor is capable of performing an inverse wavelet transform of the filtered scalogram and determining the physiological parameter in the time domain.

21. A non-transitory computer-readable medium for use in determining a physiological parameter, the non-transitory computer-readable medium having computer program instructions recorded thereon for:

receiving a first signal corresponding to a first wavelength of light and a second signal corresponding to a second wavelength of light;

performing a continuous wavelet transform on the first signal and the second signal to produce a first transformed signal and a second transformed signal;

generating a first scalogram based at least in part on the first transformed signal;

generating a second scalogram based at least in part on the second transformed signal;

generating a scalogram mask based at least in part on the first scalogram and based at least in part on the second scalogram;

filtering one of the first scalogram and the second scalogram using at least the scalogram mask to produce a filtered scalogram; and

determining a physiological parameter based at least in part on the filtered scalogram.