WEARABLE HEART RATE MONITOR

• US 20140288392A1
• Filed: 06/03/2014
• Published: 09/25/2014
• Est. Priority Date: 06/22/2012
• Status: Active Grant

• Current Assignee: Fitbit, Inc. (Alphabet Inc.)
• Original Assignee: Fitbit, Inc. (Alphabet Inc.)
• Inventors: Hong, Jung Ook, Yuen, Shelten Gee Jao
• Granted Patent: US 9,113,794 B2
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• 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 5/02427 Details of sensor
• CPC Class Codes: A61B 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• 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 5/1118 Determining activity level
• CPC Class Codes: A61B 5/1123 Discriminating type of movement, e.g. walking or running A61B5/1116, A61B5/112 take precedence
• CPC Class Codes: A61B 5/4812 Detecting sleep stages or cycles
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/6844 Monitoring or controlling distance between sensor and tissue
• CPC Class Codes: A61B 5/6886 Monitoring or controlling distance between sensor and tissue
• CPC Class Codes: A61B 5/7235 Details of waveform analysis A61B5/349 takes precedence
• CPC Class Codes: H04L 67/12 specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks
• CPC Class Codes: H04W 4/027 using movement velocity, acceleration information
• CPC Class Codes: H04W 4/08 User group management
• CPC Class Codes: H04W 4/80 Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication
• CPC Class Codes: Y02D 30/70 : in wireless communication networks

Abstract

Some embodiments provide a wearable fitness monitoring device including a motion sensor and a photoplethysmographic (PPG) sensor. The PPG sensor includes (i) a periodic light source, (ii) a photo detector, and (iii) circuitry determining a user'"'"'s heart rate from an output of the photo detector. Some embodiments provide methods for operating a heart rate monitor of a wearable fitness monitoring device to measure one or more characteristics of a heartbeat waveform. Some embodiments provide methods for operating the wearable fitness monitoring device in a low power state when the device determines that the device is not worn by a user. Some embodiments provide methods for operating the wearable fitness monitoring device in a normal power state when the device determines that the device is worn by a user. Some embodiments provide methods for using response characteristics of the user'"'"'s skin to adjust a gain and/or light emission intensity of the heart rate monitor.

Claims

1. A method of operating a heart rate monitor of a wearable fitness monitoring device, wherein the heart rate monitor comprises a light source and a light detector, the method comprising:

(a) operating the heart rate monitor in a first mode while also operating in a skin characterization mode for determining a characteristic of a user'"'"'s skin, wherein the first mode is configured to determine one or more characteristics of the user'"'"'s heartbeat waveform, and wherein the skin characterization mode comprises generating data points representing emission intensity from the light source and corresponding detection levels from the light detector;

(b) fitting the data points of the skin characterization mode to a mathematical relationship relating light source emission intensity to light detector detection level;

(c) using the mathematical relationship to determine a light source emission intensity setting that provides a pre-determined light detector detection level identified as providing good heart rate monitor performance; and

(d) adjusting the light source emission intensity to said setting determined in (c) for operating in the first mode.

2. The method of claim 1, wherein the mathematical relationship is linear.

3. The method of claim 1, wherein the pre-determined light detector detection level was previously determined to have a high signal to noise ratio.

4. The method of claim 1, further comprising, prior to (b),

determining a slope of a line fitting the data points representing emission intensity from the light source and corresponding detection levels from the light detector;

and

setting the light source emission intensity for operating in the first mode based on the determined slope and pre-set values of emission intensity levels.

5. The method of claim 1, wherein the heart rate monitor comprises a photoplethysmographic sensor.

6. The method of claim 1, wherein the one or more characteristics of the user'"'"'s heartbeat waveform comprises the user'"'"'s heart rate.

7. The method of claim 1, wherein the light source emission intensity setting is about 120 mW or less.

8. The method of claim 1, wherein operating in the first mode and operating in the skin characterization mode are performed concurrently.

9. The method of claim 8, wherein operating in the first mode and operating in the skin characterization mode concurrently comprises periodically determining a response characteristic of the user'"'"'s skin while continuously operating in the first mode.

10. The method of claim 9, wherein operating in the skin characterization mode occurs no more than about 50% of the time.

11. The method of claim 9, wherein operating in the first mode comprises pulsing the light source in the heart rate monitor at a first frequency and detecting light from the light source, after the light has interacted with the user'"'"'s skin, at the first frequency, and wherein operating in the skin characterization mode comprises pulsing a light source in the heart rate monitor at a second frequency and detecting light from the light source, after the light has interacted with the user'"'"'s skin, at the second frequency.

12. The method of claim 11, wherein the second frequency is greater than the first frequency.

13. The method of claim 11, wherein operating in the skin characterization mode further comprises determining an intensity level and/or pattern of two or more light pulses, after the light has interacted with the user'"'"'s skin, detected at the second frequency.

14. The method of claim 1, wherein operating the heart rate monitor in the skin characterization mode comprises emitting a succession of light pulses, and wherein some of the light pulses have variable intensity and other light pulses having constant intensity compared to one another.

15. The method of claim 1, wherein operating the heart rate monitor in the skin characterization mode comprises emitting a succession of light pulses, and wherein at least two of the light pulses have variable intensity compared to one another.

16. The method of claim 15, wherein operating the heart rate monitor in the skin characterization mode comprises emitting a succession of light pulses, and wherein at least four of the light pulses have variable intensity compared to one another.

17. The method of claim 1, wherein the wearable fitness monitoring device comprises a motion detecting sensor.

18. The method of claim 17, wherein the motion detecting sensor comprises an accelerometer, a magnetometer, an altimeter, a GPS detector, gyroscope, or a combination of any of these.

19. A wearable fitness monitoring device comprising:

a motion sensor configured to provide output corresponding to motion by a user wearing the fitness monitoring device;

a photoplethysmographic sensor comprising (i) a periodic light source, (ii) a photo detector positioned to receive periodic light emitted by the periodic light source after interacting with a user'"'"'s skin, and (iii) circuitry determining a user'"'"'s heart rate from an output of the photo detector; and

control logic configured to;

(a) operate the heart rate monitor in a first mode while also operating in a skin characterization mode for determining a characteristic of a user'"'"'s skin, wherein the first mode is configured to determine one or more characteristics of the user'"'"'s heartbeat waveform, and wherein the skin characterization mode comprises generating data points representing emission intensity from the light source and corresponding detection levels from the light detector;

(b) fit the data points of the skin characterization mode to a mathematical relationship relating light source emission intensity to light detector detection level;

(c) use the mathematical relationship to determine a light source emission intensity setting that provides a pre-determined light detector detection level identified as providing good heart rate monitor performance; and

(d) adjust the light source emission intensity to said setting determined in (c) for operating in the first mode.

20. The wearable fitness monitoring device of claim 19, wherein the mathematical relationship is linear.

21. The wearable fitness monitoring device of claim 19, wherein the pre-determined light detector detection level was previously determined to have a high signal to noise ratio.

22. The wearable fitness monitoring device of claim 19, wherein the control logic is further configured to, prior to (b),

determine a slope of a line fitting the data points representing emission intensity from the light source and corresponding detection levels from the light detector;

and

set the light source emission intensity for operating in the first mode based on the determined slope and pre-set values of emission intensity levels.

23. The wearable fitness monitoring device of claim 19, wherein operating in the first mode and operating in the skin characterization mode are performed concurrently.

24. The wearable fitness monitoring device of claim 23, wherein operating in the first mode comprises pulsing the light source in the heart rate monitor at a first frequency and detecting light from the light source, after the light has interacted with the user'"'"'s skin, at the first frequency, and wherein operating in the skin characterization mode comprises pulsing a light source in the heart rate monitor at a second frequency and detecting light from the light source, after the light has interacted with the user'"'"'s skin, at the second frequency.

25. A wearable fitness monitoring device comprising:

a motion sensor configured to provide output corresponding to motion by a user wearing the fitness monitoring device; and

a photoplethysmographic sensor comprising (i) a periodic light source, (ii) a photo detector positioned to receive periodic light emitted by the periodic light source after interacting with a user'"'"'s skin, and (iii) circuitry determining a user'"'"'s heart rate from an output of the photo detector, wherein the periodic light source comprises two periodic light sources straddling the photo detector.

26. The wearable fitness monitoring device of claim 25, wherein the photoplethysmographic sensor further comprises a housing having a recess in which the photo detector is disposed.

27. The wearable fitness monitoring device of claim 26, wherein the housing of the photoplethysmographic sensor further comprises a second recess in which the periodic light source is disposed.

28. The wearable fitness monitoring device of claim 27, wherein the housing of the photoplethysmographic sensor protrudes at least about 1 mm above a base surface of the wearable fitness monitoring device and is configured to press against the user'"'"'s skin when worn.

29. The wearable fitness monitoring device of claim 28, wherein the photoplethysmographic sensor further comprises a spring configured to resist compression when the protruding housing presses against the user'"'"'s skin.

30. The wearable fitness monitoring device of claim 25, wherein the photoplethysmographic sensor further comprises an IML film over the photo detector and the periodic light source.