MOTION ARTIFACT REMOVAL BY TIME DOMAIN PROJECTION

• US 20160038045A1
• Filed: 08/07/2014
• Published: 02/11/2016
• Est. Priority Date: 08/07/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: SHAPIRO, Ian R.
• Granted Patent: US 10,758,133 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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 5/0261 using optical means, e.g. infrared light
• 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

Abstract

An algorithm for removing motion artifacts from the PPG signal in the time domain to determine heart rate is disclosed. A device for determining a heart rate of a user can include a heart rate sensor configured to generate heart rate signals when positioned on or adjacent to a user'"'"'s skin, an accelerometer configured to generate one or more acceleration signals, and processing circuitry configured to remove, in a time domain, motion artifacts from the heart rate signals based on the acceleration signals. In some examples, the removal of motion artifacts can also be based on mean-centered, variance-scaled integrated acceleration signals. In some examples, the processing circuitry can be configured to remove motion artifacts using a least squares algorithm to identify a best representation of acceleration and integrated acceleration signals in the heart rate signals.

Claims

1. A device for determining a heart rate of a user, comprising:

a sensor configured to generate first signals when positioned on or adjacent to a user'"'"'s skin;

an accelerometer configured to generate one or more acceleration signals; and

processing circuitry capable of removing, in a time domain, motion artifacts from the first signals based on the acceleration signals to determine the heart rate.

2. The device of claim 1, wherein the processing circuitry is further capable of generating one or more integrated acceleration signals from the one or more acceleration signals and removing motion artifacts from the first signals based on the acceleration signals and the integrated acceleration signals.

3. The device of claim 2, wherein the one or more integrated acceleration signals are mean-centered and scaled to have a variance matching the one or more acceleration signals used to generate the corresponding integrated acceleration signals.

4. The device of claim 2, wherein the processing circuitry is further capable of removing motion artifacts using a least squares algorithm to identify a best representation of acceleration and integrated acceleration signals in the first signals.

5. The device of claim 4, wherein the processing circuitry is further capable of:

projecting the acceleration and integrated acceleration signals; and

generating residual first signals based on the projected acceleration and integrated acceleration signals and the first signals.

6. The device of claim 4, wherein the processing circuitry is further capable of:

generating latent variables for the acceleration and integrated acceleration signals;

projecting one or more components of the generated latent variables; and

generating residual heart rate signals based on the projected one or more components of the generated latent variables and the heart rate signals.

7. The device of claim 4, wherein the processing circuitry is further capable of:

generating first latent variables for the acceleration and integrated acceleration signals during a first iteration;

projecting one or more components of the first latent variables generated during the first iteration;

generating first residual heart rate signals based on the projected one or more components of the first latent variables generated during the first iteration and the heart rate signals;

deflating the acceleration and integrated acceleration signals based on the projected one or more components of the latent variable generated during the first iteration;

generating second latent variables for the deflated acceleration and integrated acceleration signals during a second iteration;

projecting one or more components of the second latent variables generated during the second iteration; and

generating second residual heart rate signals based on the projected one or more components of the second latent variables generated during the second iteration and the first residual heart rate signals.

8. The device of claim 1, wherein the processing circuitry is further capable of:

removing motion artifacts based on heart signals and acceleration signals from a plurality of overlapping time intervals to generate a plurality of overlapping residual first signals; and

generating a final time domain heart rate signal by averaging the plurality of overlapping first signals for the time intervals.

9. The device of claim 1, the processing circuitry further capable of determining at least one of an instantaneous heart rate, heart rate variability or average heart rate based on the first signals after removing motion artifacts.

10. A method executed by processing circuitry for determining a heart rate of a user, the method comprising:

receiving first signals generated by a sensor when positioned on or adjacent to a user'"'"'s skin;

receiving acceleration signals generated by an accelerometer; and

removing, in a time domain, motion artifacts from the first signals based on the acceleration signals to determine the heart rate.

11. The method of claim 10, further comprising:

generating one or more integrated acceleration signals from the one or more acceleration signals, the one or more integrated acceleration signals mean-centered and scaled to have a variance matching the one or more acceleration signals used to generate the corresponding integrated acceleration signals; and

removing motion artifacts from the first signals based on the acceleration signals and the integrated acceleration signals.

12. The method of claim 11, further comprising:

projecting the acceleration and integrated acceleration signals; and

generating residual heart rate signals based on the projected acceleration and integrated acceleration signals and the first signals.

13. The method of claim 11, further comprising:

generating latent variables for the acceleration and integrated acceleration signals;

projecting one or more components of the generated latent variables; and

generating residual heart rate signals based on the projected one or more components of the generated latent variables and the first signals.

14. The method of claim 11, further comprising:

generating first latent variables for the acceleration and integrated acceleration signals during a first iteration;

projecting one or more components of the first latent variables generated during the first iteration;

generating first residual heart rate signals based on the projected one or more components of the first latent variables generated during the first iteration and the first signals;

deflating the acceleration and integrated acceleration signals based on the projected one or more components of the latent variable generated during the first iteration;

generating second latent variables for the deflated acceleration and integrated acceleration signals during a second iteration;

projecting one or more components of the second latent variables generated during the second iteration; and

generating second residual heart rate signals based on the projected one or more components of the second latent variables generated during the second iteration and the first residual heart rate signals.

15. The method of claim 10, wherein the first signals and acceleration signals from a plurality of overlapping time intervals are used to generate a plurality of overlapping residual heart rate signals, and the method further comprising:

generating a final time domain heart rate signal by averaging the plurality of overlapping heart rate signals for the time intervals.

16. The method of claim 10, further comprising:

measuring a time separation between two peaks in the first signals; and

determining an instantaneous heart rate based on the time separation between two peaks.

17. The method of claim 10, further comprising:

measuring a time separation between a plurality of peaks in the first signals;

determining instantaneous heart rates based on the time separation between adjacent peaks of the plurality of peaks; and

determining heart rate variability based on the determined instantaneous heart rates.

18. The method of claim 10, further comprising:

measuring a number of peaks in the first signals during a time interval; and

determining an average heart rate based on the number of peaks in the first signals during the time interval.

19. A non-transitory computer readable storage 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 method comprising:

receiving first signals generated by a sensor when positioned on or adjacent to a user'"'"'s skin;

receiving acceleration signals generated by an accelerometer; and

removing, in a time domain, motion artifacts from the first signals based on the acceleration signals to determine the heart rate.

20. The non-transitory computer readable storage medium of claim 19, the method further comprising:

generating one or more integrated acceleration signals from the one or more acceleration signals, the one or more integrated acceleration signals mean-centered and scaled to have a variance matching the one or more acceleration signals used to generate the corresponding integrated acceleration signals; and

removing motion artifacts from the first signals based on the acceleration signals and the integrated acceleration signals.

21. The non-transitory computer readable storage medium of claim 20, the method further comprising:

projecting the acceleration and integrated acceleration signals; and

generating residual heart rate signals based on the projected acceleration and integrated acceleration signals and the first signals.

22. The non-transitory computer readable storage medium of claim 20, the method further comprising:

generating latent variables for the acceleration and integrated acceleration signals;

projecting one or more components of the generated latent variables; and

generating residual heart rate signals based on the projected one or more components of the generated latent variables and the first signals.

23. The non-transitory computer readable storage medium of claim 20, the method further comprising:

generating first latent variables for the acceleration and integrated acceleration signals during a first iteration;

projecting one or more components of the first latent variables generated during the first iteration;

generating first residual heart rate signals based on the projected one or more components of the first latent variables generated during the first iteration and the first signals;

deflating the acceleration and integrated acceleration signals based on the projected one or more components of the latent variable generated during the first iteration;

generating second latent variables for the deflated acceleration and integrated acceleration signals during a second iteration;

projecting one or more components of the second latent variables generated during the second iteration; and

generating second residual heart rate signals based on the projected one or more components of the second latent variables generated during the second iteration and the first residual heart rate signals.

24. The non-transitory computer readable storage medium of claim 19, wherein the first signals and acceleration signals from a plurality of overlapping time intervals are used to generate a plurality of overlapping residual heart rate signals, and the method further comprising:

generating a final time domain heart rate signal by averaging the plurality of overlapping heart rate signals for the time intervals.

25. The non-transitory computer readable storage medium of claim 19, the method further comprising determining at least one of an instantaneous heart rate, heart rate variability or average heart rate based on the first signals after removing motion artifacts.