Heart rate path optimizer

• US 9,867,575 B2
• Filed: 08/22/2014
• Issued: 01/16/2018
• Est. Priority Date: 08/22/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Maani, Ehsan, Culbert, Daniel J., Shapiro, Ian R.
• Primary Examiner(s): Dejong, Eric S
• Application Number:
  US14/466,890
• Publication Number:
  US 20160051201A1
• Time in Patent Office: 1,243 Days
• Field of Search: None
• CPC Class Codes: A61B 2560/0493 controlled by voice
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• 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 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• 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 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

A device for determining a heart rate of a user has a PPG sensor and an accelerometer to compensate for acceleration artifacts within the PPG signal. The device transforms time domain PPG and accelerometer signals into the frequency domain using a Fourier transformation and utilizes the Fourier coefficient magnitudes as indicative of the probability of candidate heart rate values. Candidate heart rate values are determined at sampling times over a time interval and a most probable heart rate path during the time interval is determined using a reward/penalty algorithm.

Claims

1. A device for determining a heart rate (HR) of a user comprising:

a (HR) sensor comprising a photoplethysmogram (PPG) sensor configured for providing HR signals;

an accelerometer coupled to the user; and

processing circuitry capable of;

providing HR values that have been compensated for artifacts from acceleration on the HR signals as measured by the accelerometer;

the HR values provided for each of a plurality of times over a time interval, and

selecting a path of optimum HR values across the time interval, the selected path implementing a reward for candidate paths based on a sum of probabilities of a most probable path between consecutive points of candidate paths, and implementing a penalty based on differences between HR values of the consecutive points along the candidate paths.

2. The device of claim 1, wherein providing the HR values includes transforming the HR signals into frequency domain HR signals (FDHR signals) and adding together at least a fundamental and first harmonic of Fourier component magnitudes of the FDHR signals corresponding to the HR signals to provide a harmonic boost.

3. The device of claim 2, wherein the Fourier component magnitudes are absolute values of Fourier coefficients of the FDHR signals.

4. The device of claim 1, wherein providing the HR values includes transforming the HR signals into frequency domain HR signals (FDHR signals) and low pass filtering Fourier component magnitudes of the FDHR signals.

5. The device of claim 4, wherein the low pass filtering is provided by utilizing a Gaussian convolution.

6. The device of claim 1, wherein providing the HR values includes transforming the HR signals into frequency domain HR signals (FDHR signals) and providing a peak boost to Fourier component magnitudes of the FDHR signals.

7. The device of claim 6, wherein the peak boost multiplies each local maxima of the Fourier component magnitudes by a number larger than 1.

8. The device of claim 7, wherein the Fourier component magnitudes are absolute values of Fourier coefficients of the FDHR signals.

9. The device of claim 1, wherein providing the HR values includes transforming the HR signals into frequency domain HR signals (FDHR signals), and transforming signals from the accelerometer into the frequency domain to provide frequency domain artifact signals (FDART signals) and wherein the HR values are computed based on complex conjugates of Fourier transform coefficients of the FDHR signals and the complex conjugates of Fourier transform coefficients of the FDART signals.

10. The device of claim 1, further comprising an analog to digital converter configured for converting the HR signals and signals from the accelerometer to digital signals.

11. The device of claim 10, wherein providing the HR values includes applying a Fourier transform to the HR signals and the signals from the accelerometer after applying the analog to digital conversions to obtain Fourier coefficients.

12. The device of claim 11, wherein providing the HR values includes taking an absolute value of the Fourier coefficients after applying the Fourier transform and the analog to digital conversion to obtain Fourier coefficient magnitudes.

13. The device of claim 12, wherein providing the HR values includes identifying peak values in the Fourier coefficient magnitudes and replacing the identified peak values by interpolated values based on values on opposite sides of the identified peak values and utilizing the interpolated values for compensating for artifacts from acceleration.

14. The device of claim 1,

wherein providing the HR values includes transforming the HR signals into frequency domain HR signals (FDHR signals), and transforming signals from the accelerometer into the frequency domain to provide frequency domain artifact signals (FDART signals);

wherein the HR values are computed based on complex conjugates of Fourier transform coefficients of the FDHR signals to provide HR Fourier coefficient magnitudes and the complex conjugates of Fourier transform coefficients of the FDART signals to provide acceleration Fourier coefficient magnitudes, and

wherein providing the HR values includes identifying peak values in the HR Fourier coefficient magnitudes that correspond to acceleration Fourier coefficient magnitudes and replacing the identified peak values with interpolated values based on values on opposite sides of the identified peak values.

15. The device of claim 14, the processing circuitry further capable of adding together at least a fundamental and first harmonic of Fourier component magnitudes of the FDHR signals corresponding to the HR signals to provide a harmonic boost and further providing a peak boost to Fourier component magnitudes of the FDHR signals by multiplying local maxima of the Fourier component magnitudes by a number larger than 1.

16. The device of claim 1, wherein providing the HR values includes transforming the HR signals into frequency domain HR signals (FDHR signals) and adding together at least a fundamental and first harmonic of Fourier component magnitudes of the FDHR signals corresponding to the HR signals to provide a harmonic boost and further providing a peak boost to Fourier component magnitudes of the FDHR signals by multiplying local maxima of the Fourier component magnitudes by a number larger than 1.

17. A device for determining a heart rate (HR) of a user comprising:

a HR sensor comprising a photoplethysmogram (PPG) sensor configured for providing time domain HR signals, the time domain HR signals having time domain HR components indicative of the user'"'"'s HR and time domain artifact components indicative of the user'"'"'s acceleration movements;

an accelerometer providing time domain accelerometer output signals;

processing circuitry capable of;

converting the time domain HR signals into frequency domain HR (FDHR) signal magnitudes and converting the time domain accelerometer output signal into frequency domain accelerometer (FDA) signal magnitudes, the FDHR signal magnitudes having frequency domain HR (FDHR) component magnitudes corresponding to the user'"'"'s heart rate and frequency domain artifact (FDART) component magnitudes corresponding to the FDA signals;

compensating for the FDART component magnitudes in the FDHR signal magnitudes to provide compensated FDHR component magnitudes for each of a plurality of times over a time interval; and

selecting a path of optimum HR values across the time interval based on the compensated FDHR component magnitudes for each of a plurality of times, the path selecting performed by implementing a reward for candidate paths based on a sum of the compensated FDHR component magnitudes of all points the candidate paths pass through, and a penalty based on a sum of distances between consecutive compensated FDHR component magnitudes along the candidate paths, the distances measured by differences between the HR values associated with consecutive path points.

18. The device of claim 17, wherein the processing circuitry is further capable of providing a harmonic boost to the compensated FDHR component magnitudes by adding together at least a fundamental and a first harmonic of the compensated FDHR component magnitudes.

19. The device of claim 18, wherein the processing circuitry is further capable of providing low pass filtering of the compensated FDHR component magnitudes.

20. The device of claim 19, wherein the low pass filtering is provided by utilizing a Gaussian convolution.

21. The device of claim 17, wherein the processing circuitry provides a Gaussian convolution to the compensated FDHR component magnitudes and further adds together at least a portion of a fundamental and a first harmonic of the compensated FDHR component magnitudes.

22. The device of claim 17, wherein the processing circuitry is further capable of providing a peak boost to each peak of the compensated FDHR component magnitudes.

23. The device of claim 22, wherein the peak boost multiplies each local maxima of the compensated FDHR component magnitudes by a number larger than 1.

24. The device of claim 17, wherein the processing circuitry is further capable of providing low pass filtering of the compensated FDHR component magnitudes.

25. The device of claim 24, wherein the low pass filtering is provided by utilizing a Gaussian convolution.

26. The device of claim 24, wherein the processing circuitry is further capable of providing a peak boost to each peak of the compensated FDHR component magnitudes.

27. The device of claim 26, wherein the peak boost multiplies each local maxima of the compensated FDHR component magnitudes by a number larger than 1.

28. The device of claim 17, wherein the FDHR signal magnitudes are computed based on complex conjugates of Fourier transforms of the time domain HR signals.

29. The device of claim 17, wherein converting the time domain HR signals into FDHR signal magnitudes includes applying an analog to digital conversion to the time domain HR signals.

30. The device of claim 29, wherein converting the time domain HR signals into the FDHR signal magnitudes and converting the time domain accelerometer output signal into FDA signal magnitudes further includes applying a Fourier transform to the time domain HR signals and the time domain accelerometer output signals after applying an analog to digital conversion.

31. The device of claim 30, wherein the FDHR signal magnitudes and the FDA signal magnitudes are computed by taking an absolute magnitude of Fourier coefficients after applying the Fourier transform and the analog to digital conversion.

32. The device of claim 31, wherein compensating for the FDART component magnitudes to provide the FDHR component magnitudes for each of a plurality of times over the time interval includes identifying peak values in the FDART component magnitudes that exceed a first threshold and replacing the identified peak values by interpolated values based on values on opposite sides of the identified peak values and utilizing the interpolated values for compensating for artifacts from acceleration.

33. The device of claim 17, wherein compensating for the FDART component magnitudes to provide the FDHR component magnitudes for each of a plurality of times over the time interval includes identifying peak values in the FDART component magnitudes that exceed a first threshold and replacing the identified peak values by interpolated values based on values on opposite sides of the identified peak values and utilizing the interpolated values for compensating for artifacts from acceleration.

34. A method of determining a HR of a user comprising:

providing heart rate (HR) signals from a HR sensor comprising a photoplethysmogram (PPG) sensor configured to be positioned on or closely adjacent the user'"'"'s skin;

providing accelerometer output signals from an accelerometer coupled to the user'"'"'s body;

providing HR values based on compensating for artifacts in the HR signals, the artifacts determined from the accelerometer output signals, the HR values provided for each of a plurality of times over a time interval; and

selecting a path of optimum HR values across the time interval, the selected path implementing a reward for candidate paths based on a sum of probabilities of a most probable path between consecutive points of the candidate paths, and a penalty based on differences between HR values of the consecutive points along the candidate paths.

35. The method of claim 34, wherein providing the HR values includes adding together at least a fundamental and first harmonic of Fourier component magnitudes associated with the HR signals.

36. The method of claim 35, wherein providing the HR values includes low pass filtering of the Fourier component magnitudes.

37. The method of claim 36, wherein the low pass filtering is provided by utilizing a Gaussian convolution.

38. The method of claim 35, wherein providing the HR values includes providing a peak boost to each peak of the Fourier component magnitudes.

39. The method of claim 38, wherein providing the peak boost comprises multiplying each local maxima of the Fourier component magnitudes by a number larger than 1.

40. The method of claim 34, wherein providing the HR values includes providing low pass filtering of Fourier component magnitudes associated with the HR signals.

41. The method of claim 40, wherein providing the low pass filtering comprises utilizing a Gaussian convolution.

42. The method of claim 34, wherein the HR values are computed based on complex conjugates of Fourier transforms of the HR signals and signals from the accelerometer.

43. The method of claim 34, wherein providing the HR values includes applying an analog to digital conversion to HR signals and signals from the accelerometer.

44. The method of claim 43, wherein providing the HR values includes applying Fourier transforms to the HR signals and accelerometer output signals after applying the analog to digital conversion.

45. The method of claim 43, wherein providing the HR values includes identifying peak values in the artifacts from the accelerometer that exceed a first threshold and replacing the identified peak values by interpolated values based on values on opposite sides of the identified peak values.

46. The method of claim 34, wherein providing the HR values includes identifying peak values in the artifacts from the accelerometer that exceed a first threshold and replacing the identified peak values by interpolated values based on values on opposite sides of the identified peak values.

47. A non-transitory computer readable medium, the computer readable medium containing instructions that, when executed, perform a method for operating an electronic device, the electronic device including a processor, the non-transitory computer readable medium, an accelerometer and a photoplethysmogram (PPG) sensor comprising at least one light emitter, at least one light receive, the method comprising:

emitting light from the at least one light emitter;

receiving light by the at least one light receiver;

receiving heart rate (HR) signals based on the light received by the at least one light receiver;

receiving accelerometer output signals from the accelerometer;

providing HR values based on compensating for artifacts in the HR signals, the artifacts determined from the accelerometer output signals the HR values provided for each of a plurality of time values over a time interval; and

selecting a path of optimum HR values across the time interval, the selected path implementing a reward for candidate paths based on a sum of probabilities of the most probable path between consecutive points of candidate paths, and a penalty based on differences between HR values of the consecutive points along the candidate paths.