Motion cancellation of optical input signals for physiological pulse measurement

• US 7,993,276 B2
• Filed: 10/13/2005
• Issued: 08/09/2011
• Est. Priority Date: 10/15/2004
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Basis Science Incorporated (Intel Corporation)
• Inventors: Harris, Paul, Alfini, Susan S., Bina, Mark J., Geatz, Michael W., Lucke, Lori E., Nazarian, Richard A., Evans, Don W. E.
• Primary Examiner(s): Mallari; Patricia C
• Assistant Examiner(s): D'ANGELO, MICHAEL J
• Application Number:
  US11/250,011
• Publication Number:
  US 20060084879A1
• Time in Patent Office: 2,126 Days
• Field of Search: 600500-504, 600/301, 600/323, 600/310, 600/393, 600/493
• 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 method of measuring a user pulse rate during physical exercise or activity, said method comprising:

transmitting light from a light source into body tissue;

receiving reflected light from said body tissue with a photo detector to produce a pulse signal, the reflected light indicative of overall vascular activity of the user;

amplifying the pulse signal and applying a direct current compensation to the pulse signal;

measuring regular motion of the user;

measuring erratic motion of the user; and

by use of a microprocessor, 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;

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;

wherein said signal conditioning comprises;

sampling and filtering said pulse signals with a non-adaptive low-pass filter 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;

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.

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

transmitting light from 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;

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;

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;

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.