Motion artifact cancelation

Patent metadata

Field	Value
Publication number	US-2016296173-A1
Application number	US-201315038420-A
Country	US
Kind code	A1
Filing date	Dec 30, 2013
Priority date	Dec 30, 2013
Publication date	Oct 13, 2016
Grant date	—

Abstract

A photoplethysmogram (PPG) signal may be obtained from a pulse oximeter, which employs a light emitter and a light sensor to measure the perfusion of blood to the skin of a user. However, the signal may be compromised by noise due to motion artifacts. That is, movement of the body of a user may cause the skin and vasculature to expand and contract, introducing noise to the signal. To address the presence of motion artifacts, examples of the present disclosure can receive light information from two light sensors situated in a line parallel to the direction of the blood pulse wave. The light information from each sensor may include the same noise signal, and thus subtracting one from the other can result in a heart rate signal where the noise has been canceled out. In some examples, a signal from one of the light sensors may be multiplied by a scaling factor before cancellation to account for response differences in each light sensor.

First claim

1 . A method of an electronic device including one or more light emitters and a plurality of light sensors, the method comprising:
emitting light from the one or more light emitters; receiving first light information from a first light sensor, the first light sensor optically coupled to one of the one or more light emitters; receiving second light information from a second light sensor, the second light sensor optically coupled to one of the one or more light emitters, wherein the second light information includes time-shifted information; and computing a heart rate signal wherein noise due to motion artifacts has been canceled by using the first and second light information.

2 . The method of claim 1 , wherein computing the heart rate signal includes:
scaling the second light information by a scaling factor; and subtracting the scaled second light information from the first light information.

3 . The method of claim 2 , further comprising:
computing the scaling factor based on the first and second light information.

4 . The method of claim 3 , wherein computing the scaling factor is further based on a heart rate signal template.

5 . The method of claim 1 , wherein the computed heart rate signal is a differential of an actual heart rate signal.

6 . The method of claim 1 , wherein computing the heart rate signal includes subtracting the second light information from the first light information.

7 . The method of claim 1 , further comprising multiplying the computed heart rate signal by a scaling factor.

8 . The method of claim 1 , wherein both the first light information and the second light information contain the same noise due to motion artifacts.

9 .- 16 . (canceled)

17 . An electronic device, comprising:
a first light emitter configured to emit first light, the first light including first light information; a second light emitter configured to emit second light, the second light including second light information, the second light information including time-shifted information; a first light sensor configured to receive a reflection of the first light; a second light sensor configured to receive a reflection of the second light; and a processor configured to:
compute a heart rate signal using first and second light information, wherein noise due to motion artifacts has been canceled.

18 . The electronic device of claim 17 , wherein computing the heart rate signal includes:
scaling the second light information by a scaling factor; and subtracting the scaled second light information from the first light information.

19 . The electronic device of claim 18 , the method further comprising:
computing the scaling factor based on the first and second light information.

20 . The electronic device of claim 19 , wherein computing the scaling factor is further based on a heart rate signal template.

21 . The electronic device of claim 17 , wherein the computed heart rate signal is a differential of an actual heart rate signal.

22 . The electronic device of claim 17 , wherein computing the heart rate signal includes subtracting the second light information from the first light information.

23 . The electronic device of claim 17 , the method further comprising multiplying the computed heart rate signal by a scaling factor.

24 . The electronic device of claim 17 , wherein both the first light information and the second light information contain the same noise due to motion artifacts.

25 . The electronic device of claim 17 , wherein the first and second light sensors are situated in a line parallel to a direction of a blood pulse wave included in the user.

26 . The electronic device of claim 17 , wherein the time-shifted information is based on a distance between the first and second light sensors and a blood pulse wave velocity.

27 . The electronic device of claim 17 , wherein a distance between the first and second light sensors is such that noise in the first light information is same as noise in the second light information.

28 . The electronic device of claim 17 , wherein one or more of the first and second light emitters are configured to emit one or more of infrared, green, amber, blue, and red light.

Assignees

• Apple Inc

Inventors

• Culbert Daniel J

Classifications

• A61B5/02438

  with portable devices, e.g. worn by the patient · CPC title

• A61B5/02433

  for infrared radiation · CPC title

• A61B5/7475

  User input or interface means, e.g. keyboard, pointing device, joystick · CPC title

• A61B5/7278

  Artificial waveform generation or derivation, e.g. synthesizing signals from measured signals · CPC title

• A61B5/7214 Primary

  using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths · CPC title