Motion cancellation of optical input signals for physiological pulse measurement

• US 20060084879A1
• Filed: 10/13/2005
• Published: 04/20/2006
• Est. Priority Date: 10/15/2004
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Basis Science Incorporated (Intel Corporation)
• Inventors: Lucke, Lori E., Harris, Paul, Alfini, Susan S., Nazarian, Richard A., Bina, Mark J., Geatz, Michael W., Evans, Don W. E.
• Granted Patent: US 7,993,276 B2
• Time in Patent Office: Days
• US Class Current: 600/500
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• 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 5/7239 using differentiation including higher order derivatives

Abstract

A pulse rate sensor that includes an accelerometer for measuring periodic motion and a piezo sensor for detecting erratic motion is capable of more accurately determining pulse rate by accounting for these types of motion. The pulse rate sensor in accordance with the present invention diminishes pulse rate signal degradation due to erratic motion through a combination of algorithms that control signal boosting, waveform refinement and signal noise suppression.

Claims

1. A pulse rate sensor for measuring a physiological parameter of an individual comprising:

an emitter for transmitting a light source into body tissue;

a photo detector for receiving reflected light from said body tissue and producing a photo detector output signal indicative of reflected light;

an accelerometer for measuring regular motion of the individual and producing an accelerometer output signal indicative of the regular motion;

a contact type motion sensor for measuring erratic motion of the user and producing a contact type motion sensor output signal indicative of the erratic motion; and

a microprocessor for receiving the photo detector output signal, the accelerometer output signal, and the contact type motion sensor output signal, and determining the pulse rate of the individual, wherein the pulse rate is determined by conditioning the photo detector output signal and removing portions of the conditioned photo detector output caused by regular motion and erratic motion of the individual.

2. The pulse rate sensor of claim 1 wherein said transmitted light source lies in the near infrared region.

3. The pulse rate sensor of claim 1 wherein said emitter comprises a plurality of light emitting diodes.

4. The pulse rate sensor of claim 1 wherein said photo detector is a reflective infra-red sensor.

5. The pulse rate sensor of claim 1 wherein said accelerometer is a two-dimensional accelerometer.

6. The pulse rate sensor of claim 1 wherein said sensor is encapsulated in a watch module for wrist-based sensing.

7. The pulse rate sensor of claim 6 wherein said watch module includes a universal serial bus port to automatically upload data, a radio frequency identification tag to uniquely identify said watch module, wherein said watch module is further capable of receiving firmware updates.

8. The pulse rate sensor of claim 1 wherein said contact type motion sensor comprises a piezo sensor and said contact type motion sensor output signal comprises a piezo sensor output signal.

19. The pulse rate sensor of claim 1 wherein the microprocessor removes portions of the conditioned photo detector output caused by regular motion and erratic motion of the individual by transforming the photo detector output signal, the accelerometer output signal, and the piezo sensor output signal to the frequency domain and removing unwanted frequency components.

20. The pulse rate detector of claim 1 wherein the pulse rate is determined by detecting peaks in the conditioned photo detector output signal.

9. A method of measuring a user pulse rate during physical exercise or activity, said method comprising:

transmitting a light source into body tissue;

receiving reflected light from said body tissue, the reflected light indicative of overall vascular activity of the user;

measuring regular motion of the user;

measuring erratic motion of the user; and

calculating pulse rate of said user based upon the received reflected light by eliminating portions caused by the measured regular motion of the user and the erratic motion of the user.

10. The method of claim 9 wherein the transmitted light is generated by an optical emitter, the reflected light is measured by a photo detector to produce a pulse signal, the regular motion is measured by an accelerometer and the erratic motion is measured by a piezo sensor, and wherein a microprocessor receives signals from the photo detector, accelerometer and piezo sensor to allow signal conditioning and the calculation of pulse rate.

11. The method of measuring a user pulse rate during physical exercise or activity of claim 10 wherein said signal conditioning comprises:

sampling and filtering said pulse signals to produce filtered signals;

applying direct current compensation to said filtered signals;

discriminating motion based on said direct current compensation signal; and

if no motion is detected, applying peak detection algorithms to calculate said pulse rate, else applying frequency analysis algorithms to calculate said pulse rate.

12. The method of measuring a user pulse rate during physical exercise or activity of claim 11, wherein said peak detection algorithms comprise:

taking a first derivative over said filtered signal;

computing a second derivative from said first derivative;

finding peaks within said filtered signal using said first and second derivatives; and

calculating instantaneous pulse rate as the difference between peaks in said filtered signal.

13. The method of measuring a user pulse rate during physical exercise or activity of claim 11, wherein said direct current compensation signal and said accelerometer signal undergo said frequency analysis to determine motion frequencies.

14. The method of measuring a user pulse rate during physical exercise or activity, of claim 11 wherein said frequency analysis algorithm is a fast fourier transform algorithm.

15. The method of measuring a user pulse rate during physical exercise or activity of claim 11 wherein said motion frequencies are removed from said pulse signals to allow discrimination of said pulse rate.

16. The method of measuring a user pulse rate during physical exercise or activity of claim 9 wherein said transmitted light source lies in the near infrared region.

17. The method of measuring a user pulse rate during physical exercise or activity of claim 10 wherein said emitter comprises a plurality of light emitting diodes.

18. The method of measuring a user pulse rate during physical exercise or activity of claim 10 wherein said photo detector is a reflective infra-red sensor.

21. A pulse rate sensor for measuring the pulse rate of an individual, comprising:

an emitter for transmitting a light source into body tissue, the intensity of the emitter light source being dependent upon an intensity control signal;

a photo detector for receiving reflected light from said body tissue and producing a photo detector output signal indicative of reflected light;

an accelerometer for measuring regular motion of the individual and producing an accelerometer output signal indicative of the regular motion;

a contact type motion sensor for measuring erratic motion of the user and producing a contact type motion sensor output signal indicative of the erratic motion;

a first amplifier receiving the photo detector output and a reference input, the first amplifier having a first amplified output which provides an adjusted first amplified signal;

a second amplifier for receiving the adjusted first amplified signal, a dc adjustment signal, and a variable gain adjustment signal, the second amplifier producing a second amplifier output signal which is dc adjusted based on the dc adjustment signal and which is amplified based on the variable gain adjustment signal; and

a microprocessor for receiving the photo detector output signal, the accelerometer output signal, the piezo sensor output signal, the adjusted first amplified signal and the second amplifier output signal, the microprocessor for producing the intensity control signal to provide an appropriate emitter intensity, for producing the dc adjustment signal to provide appropriate adjustment of the second amplifier, for producing the variable gain signal to provide appropriate gain for the second amplifier, and for determining the pulse rate of the individual, wherein the pulse rate is determined by monitoring the photo detector output signal the first amplifier output signal, and the second amplifier output signal and removing portions of those signals caused by regular motion and erratic motion of the individual.

22. The pulse rate sensor of claim 21 wherein the pulse is determined by detecting peaks in the second amplifier output signal after portions of those signals caused by regular motion and erratic motion of the individual have been removed.

23. The pulse rate sensor of claim 21 wherein the pulse is determined by transforming the second amplifier output signal, the accelerometer output signal and the contact type motion sensor output signal, and subtracting from the transformed second amplifier output signal those frequencies found in the transformed accelerometer output signal, the transformed contact type motion sensor output signal, wherein the pulse is determined to be equal to the remaining frequencies present.