Patent ID: 7738935

Claim:
A method for reducing effects of motion when measuring blood oxygen saturation, comprising the following steps of: (a) transmitting light having a first wavelength, light having a second wavelength and light having a third wavelength through body tissue; (b) receiving a portion of the light having the first wavelength, a portion of the light having the second wavelength and a portion of the light having the third wavelength; (c) producing a first signal based on the received portion of light having the first wavelength, a second signal based on the received portion of light having the second wavelength, and a third signal based on the received portion of light having the third wavelength; (d) determining a difference between the second signal and the first signal to produce a first plethysmography signal, and a difference between the third signal and the first signal to produce a second plethysmography signal; adjusting a first ratio between an intensity of the light having the first wavelength and an intensity of the light having the second wavelength to thereby reduce motion artifacts associated with the first plethysmography signal; and adjusting a second ratio between an intensity of the light having the first wavelength and an intensity of the light having the third wavelength to thereby reduce motion artifacts associated with the second plethysmography signal; and (e) estimating blood oxygen saturation using the first and second plethysmography signals, wherein the estimating is performed using a processor.