Systems and methods for determining oxygen saturation

• US 8,761,855 B2
• Filed: 10/10/2008
• Issued: 06/24/2014
• Est. Priority Date: 07/15/2008
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Watson, James Nicholas, Addison, Paul Stanley
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): EISEMAN, ADAM JARED
• Application Number:
  US12/249,068
• Publication Number:
  US 20100016690A1
• Time in Patent Office: 2,083 Days
• Field of Search: 600/309, 600/310, 600/322, 600/323, 600/324
• US Class Current: 600/336
• 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 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence

Abstract

According to embodiments, techniques for using continuous wavelet transforms and spectral transforms to determine oxygen saturation from photoplethysmographic (PPG) signals are disclosed. According to embodiments, a first oxygen saturation may be determined from wavelet transformed PPG signals and a second oxygen saturation may be determined from spectral transformed PPG signals. An optimal oxygen saturation may be determined by selecting one of the first and the second oxygen saturation or by combining the first and the second oxygen saturation. According to embodiments, a spectral transform of PPG signals may be performed to identify a frequency region associated with a pulse rate of the PPG signal. A continuous wavelet transform of the PPG signals at a scale corresponding to the identified frequency region may be performed to determine oxygen saturation from the wavelet transformed signal.

Claims

1. A method for determining oxygen saturation from photoplethysmographic (PPG) signals, comprising:

using a processor for;

receiving a first PPG signal and a second PPG signal;

calculating a first oxygen saturation based at least in part on continuous wavelet transforms of the first PPG signal and the second PPG signal;

calculating a second oxygen saturation based at least in part on spectral transforms of the first PPG signal and the second PPG signal; and

determining an optimal oxygen saturation based at least in part on the first oxygen saturation and the second oxygen saturation.

2. The method of claim 1 wherein performing the continuous wavelet transform of the first PPG signal and the second PPG signal comprises generating a first wavelet transformed signal and a second wavelet transformed signal.

3. The method of claim 2 wherein calculating the first oxygen saturation comprises:

identifying a pulse ridge in the first or the second wavelet transformed signals;

identifying a first value corresponding to an amplitude of the pulse ridge in the first wavelet transformed signal;

identifying a second value corresponding to an amplitude of the pulse ridge in the second wavelet transformed signal; and

performing a ratio of the first value and the second value, wherein the first oxygen saturation is calculated based at least in part on the ratio.

4. The method of claim 2 wherein calculating the first oxygen saturation comprises:

identifying a scale in the first wavelet transformed signal and the second wavelet transformed signal that corresponds to pulse rate;

using the scale to identify a first amplitude in the first wavelet transformed signal;

using the scale to identify a second amplitude in the second wavelet transformed signal; and

performing a ratio of the first amplitude and the second amplitude, wherein the first oxygen saturation is calculated based at least in part on the ratio.

5. The method of claim 1 wherein determining the optimal oxygen saturation comprises performing a weighted average of the first oxygen saturation and the second oxygen saturation.

6. The method of claim 1 wherein determining the optimal oxygen saturation comprises selecting the first oxygen saturation or the second oxygen saturation based at least in part on a confidence indicator.

14. The method of claim 5, wherein performing the weighted average comprises comparing a first confidence value associated with the first oxygen saturation and a second confidence value associated with the second oxygen saturation, and assigning first and second weights based on the first and second confidence values.

15. The method of claim 1, wherein calculating the second oxygen saturation comprises:

identifying a first value corresponding to a frequency peak in the spectral transform of the first PPG signal;

identifying a second value corresponding to a frequency peak in the spectral transform of the second PPG signal; and

performing a ratio of the first and second values, wherein the second oxygen saturation is calculated based at least in part on the ratio.

16. The method of claim 1, wherein calculating the second oxygen saturation based at least in part on spectral transforms comprises performing Fourier transforms of the first and second PPG signals.

17. The method of claim 1, wherein determining the optimal oxygen saturation comprises comparing a difference between the first oxygen saturation and the second oxygen saturation to a threshold value.

18. The method of claim 17, wherein, when the difference exceeds the threshold value, determining the optimal oxygen saturation comprises selecting the first or the second oxygen saturation based on at least one of a more likely value, a more stable value, a value closer to a previous optimal oxygen saturation, or an assigned priority.

19. The method of claim 1, wherein determining the optimal oxygen saturation comprises selecting the first or the second oxygen saturation based on at least one of a more likely value, a more stable value, a value closer to a previous optimal oxygen saturation, a confidence value, or an assigned priority.

20. The method of claim 1, further comprising identifying, from the spectral transforms of the first and second PPG signals, a frequency region associated with a pulse rate of the PPG signal, and wherein the continuous wavelet transforms of the first and second PPG signals are performed at a scale corresponding to the identified frequency.

21. The method of claim 1, further comprising comparing the first oxygen saturation and the second oxygen saturation to an expected value, wherein determining an optimal oxygen saturation comprises determining an optimal oxygen saturation based at least in part on the comparison.

7. A system for determining oxygen saturation from photoplethysmographic (PPG) signals, comprising:

a wavelet processor capable of calculating a first oxygen saturation based at least in part on continuous wavelet transforms of a first received PPG signal and a second received PPG signal;

a spectral processor capable of calculating a second oxygen saturation based at least in part on spectral transforms of the first received PPG signal and the second received PPG signal; and

an SpO₂ processor capable of determining an optimal oxygen saturation based at least in part on the first oxygen saturation and the second oxygen saturation.

8. The system of claim 7 wherein the wavelet processor is capable of performing a continuous wavelet transform of the first PPG signal to generate a first wavelet transformed signal and performing a continuous wavelet transform of the second PPG signal to generate a second wavelet transformed signal.

9. The system of claim 8 wherein calculating the first oxygen saturation comprises:

identifying a pulse ridge in the first or the second wavelet transformed signals;

identifying a first value corresponding to an amplitude of the pulse ridge in the first wavelet transformed signal;

identifying a second value corresponding to an amplitude of the pulse ridge in the second wavelet transformed signal; and

performing a ratio of the first value and the second value, wherein the first oxygen saturation is calculated based at least in part on the ratio.

10. The system of claim 8 wherein calculating the first oxygen saturation comprises:

identifying a scale in the first wavelet transformed signal and the second wavelet transformed signal that corresponds to pulse rate;

using the scale to identify a first amplitude in the first wavelet transformed signal;

using the scale to identify a second amplitude in the second wavelet transformed signal; and

performing a ratio of the first amplitude and the second amplitude, wherein the first oxygen saturation is calculated based at least in part on the ratio.

11. The system of claim 7 wherein the SpO₂ processor is capable of performing a weighted average of the first oxygen saturation and the second oxygen saturation to determine the optimal oxygen saturation.

12. The system of claim 7 wherein the SpO₂ processor is capable of selecting the first oxygen saturation or the second oxygen saturation based at least in part on a confidence indicator to determine the optimal oxygen saturation.

22. The system of claim 7, wherein determining an optimal oxygen saturation value comprises determining an optimal oxygen saturation value based at least in part on a comparison of the first oxygen saturation and the second oxygen saturation to an expected value.

13. Non-transitory computer-readable medium for use in determining oxygen saturation from a first photoplethysmographic (PPG) signal and a second PPG signal, the computer-readable medium having computer program instructions recorded thereon for:

calculating a first oxygen saturation based at least in part on continuous wavelet transforms of the first PPG signal and the second PPG signal;

calculating a second oxygen saturation based at least in part on spectral transforms of the first PPG signal and the second PPG signal; and

determining an optimal oxygen saturation based at least in part of the first oxygen saturation and the second oxygen saturation.