Patent ID: 6997879
Filing Date: 2006-02-14
Classification: A61B,A61N

Abstract:
1. A method for reducing motion artifacts when monitoring volume changes in blood vessels, comprising the following steps: (a) transmitting, from a light source implanted within a patient's body, light having a first wavelength and light having a second wavelength toward tissue within the patient's body; (b) receiving a portion of the light having the first wavelength and a portion of the light having the second wavelength reflected from the tissue; (c) producing a first signal, based on the received portion of light having the first wavelength, and a second signal, based on the received portion of light having the second wavelength; (d) subtracting one of the first and second signals from the other to produce a plethysmography signal that is representative of volume changes in blood vessels of the tissue; and (e) setting intensities such that a ratio of an intensity of the light having the first wavelength over an intensity of the light having the second wavelength is approximately equal to a ratio of an effective absorption coefficient of non-blood tissue at the second wavelength over an effective absorption coefficient of non-blood tissue at the first wavelength.