SYSTEMS AND METHODS FOR FILTERING AUTOCORRELATION PEAKS AND DETECTING HARMONICS

• US 20150230759A1
• Filed: 02/20/2015
• Published: 08/20/2015
• Est. Priority Date: 02/20/2014
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Convidien LP
• Inventors: McGonigle, Scott, Addison, Paul, Ochs, James
• Granted Patent: US 9,901,308 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• 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 5/7246 using correlation, e.g. template matching or determination of similarity
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

Systems and methods are provided for determining respiration information from physiological signals such as PPG signals. A physiological signal is processed to generate at least one respiration information signal and an autocorrelation sequence is generated based on the at least one respiration information signal. In some embodiments, a respiration peak is identified based on the autocorrelation sequence and a composite peak is generated based on the identified peak and at least one previous respiration peak. Respiration information is calculated based on the composite peak. In some embodiments, a determination is made whether the autocorrelation sequence includes an undesired harmonic. When the autocorrelation sequence includes an undesired harmonic, the autocorrelation sequence may not be used in the calculation of respiration information.

Claims

1. A method comprising:

receiving a photoplethysmograph (PPG) signal;

processing, with processing equipment, the PPG signal to generate at least one respiration information signal;

generating, with the processing equipment, an autocorrelation sequence based on the at least one respiration information signal;

identifying, with the processing equipment, a respiration peak of the autocorrelation sequence;

generating, with the processing equipment, a composite peak based on the respiration peak and at least one previous respiration peak; and

calculating, with the processing equipment, respiration information based at least in part on the composite peak.

2. The method of claim 1, further comprising:

low-pass filtering, with the processing equipment, the composite peak, wherein the respiration information is calculated based at least in part on the filtered composite peak.

3. The method of claim 1, wherein generating the composite peak comprises:

determining a weighting factor associated with at least one of the respiration peak and the at least one previous respiration peak; and

generating the composite peak based on the weighting factor, the respiration peak, and the at least one previous respiration peak.

4. The method of claim 3, wherein the weighting is based on the magnitude of the respiration peak.

5. The method of claim 1, wherein processing the PPG signal to generate at least one respiration information signal comprises calculating at least one series of morphology metric values over time, wherein the morphology metric values are indicative of one or more of amplitude modulation, frequency modulation, and baseline modulation of the PPG signal due to respiration.

6. The method of claim 1, wherein the at least one respiration information signal comprises two or more respiration information signals, the method further comprising:

generating, with the processing equipment, two or more autocorrelation sequences based on the at least two or more respiration information signals; and

combining, with the processing equipment, the two or more autocorrelation sequences to generate the autocorrelation sequence from which the respiration peak is identified.

7. The method of claim 1, further comprising:

determining, with the processing equipment, whether the autocorrelation sequence includes an undesired harmonic; and

modifying, with the processing equipment, at least one of said identifying, generating, and calculating steps when it is determined that the autocorrelation sequence includes an undesired harmonic.

8. The method of claim 1, further comprising normalizing the respiration peak, wherein the composite peak is generated based on the normalized respiration peak and the at least one previous respiration peak.

9. The method of claim 1, wherein calculating the respiration information comprises:

identifying a local maxima of the composite peak that exceeds a threshold; and

calculating the respiration information based at least in part on a lag index associated with the local maxima.

10. The method of claim 1, wherein the respiration information comprises respiration rate.

11. A system comprising:

an input for receiving a photoplethysmograph (PPG) signal; and

processing equipment configured for;

processing the PPG signal to generate at least one respiration information signal;

generating an autocorrelation sequence based on the at least one respiration information signal;

identifying a respiration peak of the autocorrelation sequence;

generating a composite peak based on the respiration peak and at least one previous respiration peak; and

calculating respiration information based at least in part on the composite peak.

12. The system of claim 11, wherein the processing equipment is further configured for:

low-pass filtering the composite peak, wherein the respiration information is calculated based at least in part on the filtered composite peak.

13. The system of claim 11, wherein generating the composite peak comprises:

determining a weighting factor associated with at least one of the respiration peak and the at least one previous respiration peak; and

generating the composite peak based on the weighting factor, the respiration peak, and the at least one previous respiration peak.

14. The system of claim 13, wherein the weighting is based on the magnitude of the respiration peak.

15. The system of claim 11, wherein processing the PPG signal to generate at least one respiration information signal comprises calculating at least one series of morphology metric values over time, wherein the morphology metric values are indicative of one or more of amplitude modulation, frequency modulation, and baseline modulation of the PPG signal due to respiration.

16. The system of claim 11, wherein the at least one respiration information signal comprises two or more respiration information signals and wherein the processing equipment is further configured for:

generating two or more autocorrelation sequences based on the at least two or more respiration information signals; and

combining the two or more autocorrelation sequences to generate the autocorrelation sequence from which the respiration peak is identified.

17. The system of claim 11, wherein the processing equipment is further configured for:

determining whether the autocorrelation sequence includes an undesired harmonic; and

modifying at least one of said identifying, generating, and calculating steps when it is determined that the autocorrelation sequence includes an undesired harmonic.

18. The system of claim 11, wherein the processing equipment is further configured for normalizing the respiration peak, wherein the composite peak is generated based on the normalized respiration peak and the at least one previous respiration peak.

19. The system of claim 11, wherein calculating the respiration information comprises:

identifying a local maxima of the composite peak that exceeds a threshold; and

calculating the respiration information based at least in part on a lag index associated with the local maxima.

20. The system of claim 11, wherein the respiration information comprises respiration rate.

21-40. -40. (canceled)