SYSTEMS AND METHODS FOR DETERMINING RESPIRATION INFORMATION USING PHASE LOCKED LOOP

• US 20130172767A1
• Filed: 01/04/2012
• Published: 07/04/2013
• Est. Priority Date: 01/04/2012
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Dripps, James, Ochs, James, Addison, Paul S.
• Granted Patent: US 9,247,896 B2
• Time in Patent Office: Days
• US Class Current: 600/529
• 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 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 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 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• 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
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence

Abstract

A patient monitoring system may receive a physiological signal such as a photoplethysmograph (PPG) signal that exhibits frequency and amplitude modulation based on respiration. A phase locked loop may generate a frequency demodulated signal and an amplitude demodulated signal from the PPG signal. An autocorrelation sequence may be generated for each of the frequency demodulated signal and the amplitude demodulated signal. The autocorrelation sequences may be combined and respiration information may be determined based on the combined autocorrelation sequence.

Claims

1. A method for determining respiration information, the method comprising:

receiving a photoplethysmograph (PPG) signal;

generating, using processing equipment, an oscillator signal;

adjusting, using the processing equipment, the oscillator signal based on a phase difference between the PPG signal and the oscillator signal;

generating, using the processing equipment, a demodulated signal based on the PPG signal and the oscillator signal; and

determining, using the processing equipment, the respiration information based on the demodulated signal.

2. The method of claim 1, wherein generating the demodulated signal further comprises:

generating a product signal from the PPG signal and the oscillator signal; and

low pass filtering the product signal.

3. The method of claim 1, wherein determining the respiration information comprises:

generating an autocorrelation sequence based on the demodulated signal; and

determining the respiration information based on the autocorrelation sequence.

4. The method of claim 1, wherein the demodulated signal comprises an amplitude demodulated signal.

5. The method of claim 1, wherein the demodulated signal comprises a frequency demodulated signal.

6. The method of claim 5, further comprising:

shifting, using the processing equipment, a phase of the oscillator signal; and

generating, using the processing equipment, an amplitude demodulated signal based on the PPG signal and the phase shifted oscillator signal.

7. The method of claim 6, wherein determining the respiration information comprises:

generating a first autocorrelation sequence based on the frequency demodulated signal;

generating a second autocorrelation sequence based on the amplitude demodulated signal;

generating a combined autocorrelation sequence based on the first autocorrelation sequence and the second autocorrelation sequence; and

determining the respiration information based on the combined autocorrelation sequence.

8. The method of claim 7, wherein generating the combined autocorrelation sequence comprises:

determining a first confidence metric based on the first autocorrelation sequence;

determining a second confidence metric based on the second autocorrelation sequence; and

generating the combined autocorrelation sequence of the first confidence metric, the first autocorrelation sequence, the second confidence metric, and the second autocorrelation sequence.

9. The method of claim 1, wherein the PPG signal is band pass filtered based on a heart rate associated with the PPG signal.

10. The method of claim 1, wherein the oscillator signal is generated using voltage controlled oscillator or a modulo-N counter.

11. A patient monitoring system comprising:

an interface configured to receive a photoplethysmograph (PPG) signal;

a phase detector coupled to the interface;

an oscillator coupled to the phase detector, wherein the oscillator is configured to adjust the phase of an oscillator signal based on a phase difference between the PPG signal and the oscillator signal; and

a processor configured to;

generate a demodulated signal based on the PPG signal and the oscillator signal, and

determine the respiration information based on the demodulated signal.

12. The patient monitoring system of claim 11, wherein the processor is further configured to:

generate a product signal from the PPG signal and the oscillator signal; and

low pass filter the product signal.

13. The patient monitoring system of claim 11, wherein the processor is further configured to:

generate an autocorrelation sequence based on the demodulated signal; and

determine the respiration information based on the autocorrelation sequence.

14. The patient monitoring system of claim 11, wherein the demodulated signal comprises an amplitude demodulated signal.

15. The patient monitoring system of claim 11, wherein the demodulated signal comprises a frequency demodulated signal.

16. The patient monitoring system of claim 15, wherein the processor is further configured to:

shift the phase of the oscillator signal; and

generate an amplitude demodulated signal based on the PPG signal and the phase shifted oscillator signal.

17. The patient monitoring system of claim 16, wherein the processor is further configured to:

generate a first autocorrelation sequence based on the frequency demodulated signal;

generate a second autocorrelation sequence based on the amplitude demodulated signal;

generate a combined autocorrelation sequence based on the first autocorrelation sequence and the second autocorrelation sequence; and

determine the respiration information based on the combined autocorrelation sequence.

18. The patient monitoring system of claim 17, wherein the processor is further configured to:

associate a first weighting factor with the first autocorrelation sequence;

associate a second weighting weight with the second autocorrelation sequence; and

generate the combined autocorrelation sequence of the first weighting factor, the first autocorrelation sequence, the second weighting factor, and the second autocorrelation sequence.

19. The patient monitoring system of claim 11, wherein the PPG signal is band pass filtered based on a heart rate associated with the PPG signal.

20. The patient monitoring system of claim 11, wherein the oscillator comprises a voltage controlled oscillator or a modulo-N counter.