Systems And Methods For Determining Oxygen Saturation

• US 20100016690A1
• Filed: 10/10/2008
• Published: 01/21/2010
• 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
• Granted Patent: US 8,761,855 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• 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 PPG signals, comprising:

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 of 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 an 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 an optimal oxygen saturation comprises selecting the first oxygen saturation or the second oxygen saturation based at least in part on a confidence indicator.

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

a wavelet processor capable of calculating a first oxygen saturation based at least in pail 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 pall 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 pail on a confidence indicator to determine the optimal oxygen saturation.

13. A method for determining oxygen saturation from PPG signals, comprising:

receiving a first PPG signal and a second PPG signal;

performing a spectral transform of the first and the second PPG signals to produce a first and a second spectral transformed signals;

identifying from the first and the second spectral transformed signals a frequency region associated with a pulse rate of the PPG signals;

performing a continuous wavelet transform of the first and the second PPG signals at a scale corresponding to the identified frequency region to produce a first and a second wavelet transformed signals; and

determining oxygen saturation based at least in part upon the wavelet transformed signals.

14. The method of claim 13 wherein identifying the frequency region associated with a pulse rate of the PPG signal comprises identifying peaks in the spectral transformed signals.

15. The method of claim 13 wherein determining oxygen saturation based at least in part upon the wavelet transformed signal comprises determining oxygen saturation over time.

16. A system for determining a pulse rate from a PPG signal, comprising:

a spectral processor capable of performing a spectral transform of a first received PPG signal and a second received PPG signal identifying a frequency region associated with a pulse rate of the PPG signals spectral transformed signals; and

a wavelet processor capable of performing a continuous wavelet transform of the first and the second received PPG signals at a scale corresponding to the identified frequency region to produce a first and a second wavelet transformed signals; and

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

17. The system of claim 16 wherein the spectral processor is capable of identifying peaks in the spectral transformed signals to identify the frequency region associated with the pulse rate.

18. The system of claim 16 wherein the wavelet processor is capable of determining oxygen saturation over time.

19. Computer-readable medium for use in determining oxygen saturation from a first 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.

20. Computer-readable medium for use in determining oxygen saturation from a first PPG signal and a second PPG signal, the computer-readable medium having computer program instructions recorded thereon for:

performing a spectral transform of the first and the second PPG signals to produce a first and a second spectral transformed signals;

identifying from the first and the second spectral transformed signals a frequency region associated with a pulse rate of the PPG signals;

performing a continuous wavelet transform of the first and the second PPG signals at a scale corresponding to the identified frequency region to produce a first and a second wavelet transformed signals; and

determining oxygen saturation from the wavelet transformed signals.