Multi-wavelength pulse oximetry

• US 10,568,525 B1
• Filed: 12/12/2016
• Issued: 02/25/2020
• Est. Priority Date: 12/14/2015
• Status: Active Grant

• Current Assignee: Fitbit, Inc. (Alphabet Inc.)
• Original Assignee: Fitbit, Inc. (Alphabet Inc.)
• Inventors: Wu, Anjian, Sarantos, Chris H., Richards, Peter W., Yuen, Shelten Gee Jao
• Primary Examiner(s): Winakur, Eric F
• Assistant Examiner(s): Mustansir, Abid A
• Application Number:
  US15/376,542
• Time in Patent Office: 1,170 Days
• CPC Class Codes: A61B 5/0004 characterised by the type of physiological signal transmitted
• CPC Class Codes: A61B 5/0022 Monitoring a patient using a global network, e.g. telephone networks, internet
• 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 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• 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

In one embodiment, a method for creating a blood oxygen saturation (SpO₂) value, the method comprises receiving one or more photoplethysmography (PPG) signals for SpO₂ detection from one or more PPG sensors; receiving one or more PPG signals for characterizing a heart rate from the one or more PPG sensors; using the one or more PPG signals for SpO₂ detection, forming one or more SpO₂ datasets wherein the SpO₂ datasets respectively comprise one or more noise components; removing the one or more noise components from the one or more SpO₂ datasets that are inconsistent with a feature of the one or more PPG signals characterizing the heart rate to produce one or more filtered SpO₂ datasets; and using the one or more filtered SpO₂ datasets, creating and storing the SpO₂.

Claims

1. A method for determining a blood oxygen saturation (SpO₂) value, the method comprising:

receiving one or more photoplethysmography (PPG) signals for SpO₂ detection from one or more PPG sensors;

receiving one or more PPG signals for characterizing a heart rate from the one or more PPG sensors;

forming one or more SpO₂ datasets using the one or more PPG signals for SpO₂ detection, wherein the one or more SpO₂ datasets respectively comprise one or more noise components that are inconsistent with a frequency feature of the one or more PPG signals characterizing the heart rate;

filtering the one or more SpO₂ datasets to remove the one or more noise components that are inconsistent with the frequency feature of the one or more PPG signals characterizing the heart rate to produce one or more filtered SpO₂ datasets;

determining, using the one or more filtered SpO₂ datasets, the SpO₂ value; and

storing the SpO₂ value.

2. The method of claim 1, further comprising receiving the one or more PPG signals for SpO₂ detection from both a first PPG sensor from the one or more PPG sensors and a second PPG sensor from the one or more PPG sensors, wherein the first PPG sensor is configured to detect a first set of wavelengths of light and the second PPG sensor is configured to detect a second set of wavelengths of light.

3. The method of claim 1, further comprising receiving the one or more PPG signals for SpO₂ detection from one or more detectors of the one or more PPG sensors that are configured to detect light with one or more wavelengths selected from a range of 650 nm to 950 nm.

4. The method of claim 1, further comprising receiving the one or more PPG signals for characterizing the heart rate from a PPG sensor having a light source that emits predominantly green light.

5. The method of claim 1, further comprising receiving the one or more PPG signals for characterizing the heart rate from one or more detectors of the one or more PPG sensors that are configured to detect light with one or more wavelengths selected from a range of 495 nm to 570 nm.

6. The method of claim 1, wherein the one or more PPG sensors are in a monitoring device which is configured, when worn, to align the one or more PPG sensors proximate to a user'"'"'s skin.

7. The method of claim 6, further comprising receiving the one or more PPG signals for characterizing the heart rate from the one or more PPG sensors in the monitoring device.

8. The method of claim 1, further comprising receiving the one or more PPG signals for characterizing the heart rate from one or more detectors that are proximate to one or more light sources emitting green light.

9. The method of claim 1, further comprising receiving the one or more PPG signals for determining SpO₂ from one or more detectors that are proximate to two or more spaced-apart pairs of light sources, each pair of light sources including a light source configured to emit light wavelengths in the red light spectrum and another light source configured to emit light in the infrared light spectrum.

10. The method of claim 9, further comprising:

(a) activating a first pair of the two or more spaced apart pairs of light sources while a second pair of the two or more pairs of light sources is deactivated;

(b) receiving, from the one or more detectors, a first red PPG signal and a first infrared PPG signal from the one or more PPG signals for determining SpO₂ and associated with the first pair of the two or more pairs of light sources;

(c) determining that at least one of a first red PPG signal quality of the first red PPG signal and a first infrared PPG signal quality is below a stored minimum red PPG signal value or a stored minimum infrared PPG signal value, respectively;

(d) activating, based on the determining of (c), the second pair of the two or more pairs of light sources,

(e) receiving, from the one or more detectors, a second red PPG signal and a second infrared PPG signal associated with the second pair;

(f) determining that a second red PPG signal quality of the second red PPG signal is above the stored minimum red PPG signal value and that a second infrared PPG signal quality is above the stored minimum infrared PPG signal value; and

(g) determining the one or more SpO₂ datasets using the second red PPG signal and the second infrared PPG signal as the one or more PPG signals for SpO₂ detection.

11. The method of claim 10, further comprising deactivating the first pair based on the determining of (c).

12. The method of claim 9, further comprising:

(a) activating a first pair of the two or more spaced-apart pairs of light sources while at least one other pair of the two or more spaced-apart pairs of light sources is deactivated;

(b) receiving, from the one or more detectors, a first red PPG signal and a first infrared PPG signal from the one or more PPG signals for determining SpO₂ and associated with the first pair of the two or more pairs of light sources;

(c) receiving a temperature signal from a temperature sensor;

(d) determining that the temperature signal is less than a stored minimum temperature signal;

(e) activating, based on the determining of (d), a second pair of the two or more pairs of light sources;

(f) receiving, from the one or more detectors, a second red PPG signal and a second infrared PPG signal associated with the second pair of light sources;

(g) forming a combined red PPG signal using the first red PPG signal and the second red PPG signal; and

(h) forming a combined infrared PPG signal using the first infrared PPG signal and the second infrared PPG signal.

13. The method of claim 1, further comprising receiving the one or more PPG signals for determining SpO₂ from a first PPG sensor and receiving the one or more PPG signals for characterizing a heart rate from a second PPG sensor through a light filter that filters a wavelength that is different from a wavelength of light detected by at least one of the sensors.

14. The method of claim 1, wherein filtering the one or more SpO₂ datasets to produce one or more filtered SpO₂ datasets as output includes using one or more filtering techniques selected from the group consisting of:

least mean squares filtering, recursive least squares (RLS) filtering, using a template as coefficient data that is input to a matched filter, and using an adaptive filter.

15. The method of claim 1, further comprising:

(a) receiving the one or more PPG signals for determining SpO₂ from one or more detectors that are proximate to a rotatable substrate that includes a red light source and an infrared light source and is in a first rotational position;

(b) determining that a quality of the one or more of the one or more PPG signals for determining SpO₂ is less than a stored minimum PPG signal value; and

(c) rotating, responsive to the determining of (b), the rotatable substrate to a second rotational position different from the first rotational position.

16. A monitoring device for determining a blood oxygen saturation (SpO₂) value, the device comprising:

one or more processors communicatively coupled with a memory, wherein the memory stores computer-executable instructions which, when executed by the one or more processors cause the one or more processors to;

receive one or more photoplethysmography (PPG) signals for SpO₂ detection from one or more PPG sensors;

receive one or more PPG signals for characterizing a heart rate from the one or more PPG sensors;

form one or more SpO₂ datasets using the one or more PPG signals for SpO₂ detection, wherein the one or more SpO₂ datasets respectively comprise one or more noise components that are inconsistent with a frequency feature of the one or more PPG signals characterizing the heart rate;

filter the one or more SpO₂ datasets to remove the one or more noise components that are inconsistent with the frequency feature of the one or more PPG signals characterizing the heart rate to produce one or more filtered SpO₂ datasets;

determine, using the one or more filtered SpO₂ datasets, the SpO₂ value; and

store the SpO₂ value.

17. The monitoring device of claim 16, wherein:

the one or more PPG sensors includes two or more PPG sensors,

the memory further stores additional instructions which, when executed, cause the one or more processors to receive the one or more PPG signals for SpO₂ detection from both a first PPG sensor from the two or more PPG sensors and a second PPG sensor from the two or more PPG sensors,

the first PPG sensor is configured to detect a first set of wavelengths of light, and

the second PPG sensor is configured to detect a second set of wavelengths of light.

18. The monitoring device of claim 16, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to receive the one or more PPG signals for SpO₂ detection from one or more detectors configured to detect light with one or more wavelengths selected from a range of 650 nm to 950 nm.

19. The monitoring device of claim 16, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to receive the one or more PPG signals for characterizing the heart rate from a PPG sensor having a light source that emits predominantly green light.

20. The monitoring device of claim 16, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to receive the one or more PPG signals for characterizing the heart rate from one or more detectors of the one or more PPG sensors that are configured to detect light with one or more wavelengths selected from a range of 495 nm to 570 nm.

21. The monitoring device of claim 16, wherein the memory further stores additional instructions which when executed cause the one or more processors to filter the one or more SpO₂ datasets using an adaptive filter that is based on the frequency feature.

22. The monitoring device of claim 16, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to filter the one or more SpO₂ datasets using an a least squares filtering technique selected from the group consisting of least mean squares (LMR) and recursive least squares (RLS) and based on the frequency feature.

23. The monitoring device of claim 16, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to filter the one or more SpO₂ datasets using an adaptive filter that includes a band-pass filter that is tuned in real-time based on the frequency feature.

24. The monitoring device of claim 16, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to receive the one or more PPG signals for determining SpO₂ from one or more detectors that are proximate to two or more spaced-apart pairs of light sources, each pair of light sources including a light source configured to emit light wavelengths in the red light spectrum and another light source configured to emit light in the infrared light spectrum.

25. The monitoring device of claim 24, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to:

(a) activate a first pair of the two or more spaced apart pairs of light sources while a second pair of the two or more pairs of light sources is deactivated;

(b) receive, from the one or more detectors, a first red PPG signal and a first infrared PPG signal from the one or more PPG signals for determining SpO₂ and associated with the first pair of the two or more pairs of light sources;

(c) determine that at least one of a first red PPG signal quality of the first red PPG signal and a first infrared PPG signal quality is below a stored minimum red PPG signal value or a stored minimum infrared PPG signal value, respectively;

(d) activate, based on the determination of (c), the second pair of the two or more pairs of light sources;

(e) receive, from the one or more detectors, a second red PPG signal and a second infrared PPG signal associated with the second pair;

(f) determine that a second red PPG signal quality of the second red PPG signal is above the stored minimum red PPG signal value and that a second infrared PPG signal quality is above the stored minimum infrared PPG signal value; and

(g) determine the one or more SpO₂ datasets using the second red PPG signal and the second infrared PPG signal as the one or more PPG signals for SpO₂ detection.

26. The monitoring device of claim 25, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to deactivate the first pair based on the determination of (c).

27. The monitoring device of claim 24, wherein the memory further stores additional instructions which, when executed, cause the one or more processors to perform:

(a) activate a first pair of the two or more spaced-apart pairs of light sources while at least one other pair of the two or more spaced-apart pairs of light sources is deactivated;

(b) receive, from the one or more detectors, a first red PPG signal and a first infrared PPG signal from the one or more PPG signals for determining SpO₂ and associated with the first pair of the two or more pairs of light sources;

(c) receive a temperature signal from a temperature sensor;

(d) determine that the temperature signal is less than a stored minimum temperature signal;

(e) activate, based on the determination of (d), a second pair of the two or more pairs of light sources;

(f) receive, from the one or more detectors, a second red PPG signal and a second infrared PPG signal associated with the second pair of light sources;

(g) form a combined red PPG signal using the first red PPG signal and the second red PPG signal; and

(h) form a combined infrared PPG signal using the first infrared PPG signal and the second infrared PPG signal.

28. The monitoring device of claim 16, wherein the memory stores further additional instructions which, when executed, cause the one or more processors to receive the one or more PPG signals for determining SpO₂ from a first PPG sensor and the one or more PPG signals for characterizing a heart rate from a second PPG sensor through a light filter that filters a wavelength that is different from a wavelength of light detected by at least one of the sensors.

29. The monitoring device of claim 16, wherein the memory stores further additional instructions which, when executed, cause the one or more processors to filter the one or more SpO₂ datasets to produce one or more filtered SpO₂ datasets as output using one or more filtering techniques selected from the group consisting of:

least mean squares filtering, recursive least squares (RLS) filtering, using a template as coefficients for a matched filter, and using an adaptive filter.

30. The monitoring device of claim 16, wherein the memory stores further instructions which, when executed, cause the one or more processors to:

(a) receive the one or more PPG signals for determining SpO₂ from one or more detectors that are proximate to a rotatable substrate that includes a red light source and an infrared light source and is in a first rotational position;

(b) determine that a quality of the one or more of the one or more PPG signals for determining SpO₂ is less than a stored minimum PPG signal value; and

(c) rotate, responsive to the determination of (b), the rotatable substrate to a second rotational position different from the first rotational position.