Heart rate monitor with time varying linear filtering

• US 9,801,587 B2
• Filed: 10/18/2016
• Issued: 10/31/2017
• Est. Priority Date: 10/19/2015
• Status: Active Grant

• Current Assignee: Garmin Switzerland GmbH (Garmin Limited)
• Original Assignee: Garmin Switzerland GmbH (Garmin Limited)
• Inventors: MacDonald, Paul R., Kulach, Christopher J.
• Primary Examiner(s): Gedeon, Brian T
• Application Number:
  US15/296,956
• Publication Number:
  US 20170105682A1
• Time in Patent Office: 378 Days
• Field of Search: None
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/0833 Measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/1112 Global tracking of patients, e.g. by using GPS
• CPC Class Codes: A61B 5/1118 Determining activity level
• CPC Class Codes: A61B 5/165 Evaluating the state of mind, e.g. depression, anxiety
• CPC Class Codes: A61B 5/4815 Sleep quality
• CPC Class Codes: A61B 5/486 Bio-feedback A61B5/375 takes precedence
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• 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 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence

Abstract

A system, method, and device for monitoring a cardiac signal of a user includes an emitter (LED) for transmitting light toward skin of the user, a receiver (photodiode) for receiving a reflection of the transmitted light and generating a light intensity signal, and a processor configured to generate a photoplethysmogram (PPG) signal based on the light intensity signal. The PPG signal includes a cardiac component, a motion component and a respiratory component. An inertial sensor provides a motion signal to the processor based on sensed movement of the device and one or more time-variant filters are configured by the processor to filter the PPG signal to isolate the cardiac component of the PPG signal based on determined filter coefficients.

Claims

1. A fitness monitor for monitoring a cardiac signal of a user, the device comprising:

an emitter configured to transmit light toward skin of the user;

a receiver configured to receive a reflection of the transmitted light and provide a photoplethysmogram (PPG) signal based on the received reflection of the transmitted light, the PPG signal including a cardiac component and a motion component;

an inertial sensor configured to provide a motion signal based on sensed movement of the fitness monitor;

a time-variant filter configured to isolate a component of the PPG signal based on filter coefficients corresponding to a desired component of the PPG signal, and

a processor coupled to the emitter, the receiver, the inertial sensor and the time-variant filter, the processor configured to;

determine one or more frequencies associated with the motion signal;

transform the PPG signal to the frequency domain;

identify, in the frequency domain, the cardiac component in the PPG signal based on the determined one or more frequencies of the motion signal and the transformed PPG signal;

determine filter coefficients based on the identified cardiac component in the PPG signal;

configure the time-variant filter with the determined filter coefficients;

filter, in the time domain via the time-variant filter, the motion component from the PPG signal to isolate the identified cardiac component; and

calculate, in the time domain, the time between successive cycles of the isolated cardiac component of the PPG signal.

2. The fitness monitor of claim 1, wherein the time-variant filter is integrated within the processor.

3. The fitness monitor of claim 1, wherein the filter coefficients are determined upon each occurrence of the cardiac component being identified based on the determined one or more frequencies of the motion signal and the transformed PPG signal.

4. The fitness monitor of claim 3, wherein the processor configures the time-variant filter with the determined filter coefficients upon each occurrence of the cardiac component being identified.

5. The fitness monitor of claim 1, wherein the processor is further configured to periodically reconfigure the time-variant filter based on the cardiac component identified in the frequency domain.

6. The fitness monitor of claim 1, further comprising a bandpass filter, wherein the processor is further configured to configure the bandpass filter to pre-condition the PPG signal by attenuating frequency components of the PPG signal below a predetermined frequency band that includes the cardiac component and/or attenuates frequency components above the predetermined frequency band that includes the cardiac component, the predetermined frequency band spanning the full range of human heart rates.

7. The fitness monitor of claim 1, wherein the cardiac component is associated with heart rate, and wherein the determined time between successive cycles of the cardiac component is the time between successive heartbeats.

8. The fitness monitor of claim 1, wherein the processor is further configured to analyze the cardiac component of the PPG signal to determine heart-rate variability, stress, recovery time, VO2 max, and/or sleep quality of the user, based on the determined time between successive cycles of the cardiac component.

9. The fitness monitor of claim 1, further comprising a user interface coupled to the processor to display information based on the isolated cardiac component.

10. The fitness monitor of claim 1, further comprising a housing to enclose the processor, the housing including a means for attaching the fitness monitor to the user.

11. The fitness monitor of claim 1, wherein the determined filter coefficients include a center frequency corresponding to a fundamental frequency of the identified cardiac component of the PPG signal, and wherein the time-variant filter isolates the identified cardiac component by passing portions of the PPG signal associated with the center frequency.

12. The fitness monitor of claim 1, wherein the processor calculates the time between successive cycles of the isolated cardiac component by identifying similar peaks, troughs, or threshold-crossings of the isolated cardiac component in the successive cycles.

13. The fitness monitor of claim 1, wherein the processor identifies the cardiac component in the frequency domain by correlating one or more peaks of a motion signal with temporally consistent spectral peaks of the PPG signal.

14. A fitness monitor for monitoring a cardiac signal of a user, the device comprising:

an emitter configured to transmit light toward skin of the user;

a receiver configured to receive a reflection of the transmitted light and provide a photoplethysmogram (PPG) signal based on the received reflection of the transmitted light, the PPG signal including a cardiac component and a motion component;

an inertial sensor configured to provide a motion signal based on sensed movement of the fitness monitor;

a time-variant filter configured to isolate a component of the PPG signal based on filter coefficients corresponding to undesired components of the PPG signal, and

a processor coupled to the emitter, the receiver, the inertial sensor and the time-variant filter, the processor configured to;

determine one or more frequencies associated with the motion signal and the PPG signal provided during a first period,

identify the motion component in the PPG signal for the first time period based on the determined one or more frequencies of the motion signal and the PPG signal,

filter, via the time-variant filter, the identified motion component from the PPG signal provided during a second time period to isolate the cardiac component of the PPG signal for the second time period, and

calculate, in the time domain, the time between successive cycles of the isolated cardiac component of the PPG signal for the second time period.

15. The fitness monitor of claim 14, wherein the first and second time periods correspond to the same period of time such that the filtered motion component is from the same instance of the PPG signal in which the motion component is identified.

16. The fitness monitor of claim 14, wherein the time-variant filter is integrated within the processor.

17. The fitness monitor of claim 14, wherein the processor is further configured to determine filter coefficients based on the identified motion component in the PPG signal for the first time period and configure the time-variant filter with the determined filter coefficients.

18. The fitness monitor of claim 14, wherein the cardiac component of the PPG signal for the second time period is isolated upon each occurrence of the motion component being identified based on the determined one or more frequencies of the motion signal and the motion component.

19. The fitness monitor of claim 14, further comprising a bandpass filter, wherein the processor is further configured to configure the bandpass filter to pre-condition the PPG signal by attenuating frequency components of the PPG signal below a predetermined frequency band that includes the cardiac component and/or attenuates frequency components above the predetermined frequency band that includes the cardiac component, the predetermined frequency band spanning the full range of human heart rates.

20. The fitness monitor of claim 14, wherein the cardiac component is associated with heart rate, and wherein the determined time between successive cycles of the cardiac component is the time between successive heartbeats.

21. The fitness monitor of claim 14, wherein the determined filter coefficients include a center frequency corresponding to a fundamental frequency of the identified motion component of the PPG signal for the first time period, and wherein the time-variant filter isolates the identified cardiac component during the second time period by not passing undesired components of the PPG signal associated with the center frequency.

22. The fitness monitor of claim 14, wherein the processor calculates the time between successive cycles of the isolated cardiac component by identifying similar peaks, troughs, or threshold-crossings of the isolated cardiac component in the successive cycles.

23. The fitness monitor of claim 14, wherein the processor identifies the motion component in the PPG signal for the first time period by correlating one or more peaks of a motion signal for the first time period with temporally consistent spectral peaks of the PPG signal.

24. A fitness monitor for monitoring a cardiac signal of a user, the device comprising:

an emitter configured to transmit light toward skin of the user;

a receiver configured to receive a reflection of the transmitted light and provide a photoplethysmogram (PPG) signal based on the received reflection of the transmitted light, the PPG signal including a cardiac component and a motion component;

an inertial sensor configured to provide a motion signal based on sensed movement of the fitness monitor;

a time-variant filter configured to isolate a component of the PPG signal based on filter coefficients corresponding to a desired component of the PPG signal, and

a processor coupled to the emitter, the receiver, the inertial sensor and the time-variant filter, the processor configured to;

determine one or more frequencies associated with the motion signal and the PPG signal provided during a first time period,

identify the cardiac component in the PPG signal for the first time period based on the determined one or more frequencies of the motion signal and the PPG signal,

filter, via the time-variant filter, the PPG signal provided for a second time to isolate the cardiac component of the PPG signal for the second time period based on the identified cardiac component, and

calculate, in the time domain, the time between successive cycles of the isolated cardiac component of the PPG signal for the second time period.

25. The fitness monitor of claim 24, wherein the time-variant filter is integrated within the processor.

26. The fitness monitor of claim 24, wherein the processor is further configured to determine filter coefficients based on the identified cardiac component in the PPG signal for the first time period and configure the time-variant filter with the determined filter coefficients.

27. The fitness monitor of claim 24, wherein the determined filter coefficients include a center frequency corresponding to a fundamental frequency of the identified cardiac component of the PPG signal, and wherein the time-variant filter isolates the identified cardiac component by passing portions of the PPG signal associated with the center frequency.

28. The fitness monitor of claim 24, wherein the processor calculates the time between successive cycles of the isolated cardiac component by identifying similar peaks, troughs, or threshold-crossings of the isolated cardiac component in the successive cycles.

29. The fitness monitor of claim 24, wherein the processor identifies the cardiac component in the PPG signal for the first time period by correlating one or more peaks of a motion signal for the first time period with temporally consistent spectral peaks of the PPG signal.