METHOD AND APPARATUS FOR DEMODULATING SIGNALS IN A PULSE OXIMETRY SYSTEM

• US 20080033265A1
• Filed: 08/20/2007
• Published: 02/07/2008
• Est. Priority Date: 04/14/1997
• Status: Active Grant

• Current Assignee: Ammar Al-Ali, Mohamed K. Diab, Walter Weber
• Original Assignee: Ammar Al-Ali, Mohamed K. Diab, Walter Weber
• Inventors: Al-Ali, Ammar, Diab, Mohamed, Weber, Walter
• Granted Patent: US 8,185,180 B2
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 2560/0242 adapted to measure environmental factors, e.g. temperature, pollution
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• 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 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7217 of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker
• CPC Class Codes: A61B 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: H04J 14/08 Time-division multiplex systems
• CPC Class Codes: H04J 3/10 Arrangements for reducing cross-talk between channels

Abstract

A method and an apparatus measure blood oxygenation in a subject. A light source is activated to cause a first emission at a first wavelength and a second emission at a second wavelength. A detector detects a composite signal indicative of an attenuation of the first and second wavelengths by tissue of a patient. The composite signal is demodulated into a first intensity signal and a second intensity signal. Blood oxygenation in the subject is determined from the first and second intensity signals. In one embodiment, demodulation is based at least in part on a period when at least one of the wavelengths is not activated. In one embodiment, a modulation of the first and second wavelengths is determined in order to avoid frequencies of ambient noise. In one embodiment, the composite signal'"'"'s sampling rate is reduced before and/or after demodulation.

Claims

1. A method of determining an indication of a physiological parameter by demodulating a composite output signal from a detector of a noninvasive optical sensor, the method comprising:

outputting activation signals to activate one or more light sources to cause emissions at least two different wavelengths;

wherein the activation signals include at least one period of inactivation;

receiving a detected composite signal indicative of an attenuation by said body tissue of said at least two different wavelengths;

demodulating said composite signal into a first intensity signal responsive to said attenuation of at least a first of the at least two wavelengths, a second intensity signal responsive to said attenuation of at least a second of the at least two wavelengths and a third signal representative of a non-physiological portion of the composite signal, wherein said demodulation is based at least in part on the inactivation; and

determining an indication of a physiological parameter of said body tissue based on one or more of said first and second intensity signals.

2. The method of claim 1, wherein demodulating further comprises using a demodulation constraint.

3. The method of claim 2, wherein using a demodulation constraint further comprises adjusting said demodulation constraint based at least in part on the composite signal.

4. The method of claim 3, wherein adjusting said demodulation constraint based at least in part on the composite signal further comprises using feedback.