Patent ID: 6594513
Filing Date: 2003-07-15
Classification: A61B

Abstract:
A non-invasive, in-vivo, in-situ spectrophotometric method of determining percent oxygen saturation of hemoglobin in blood within a part of a body exhibiting active oxidative metabolism without having to consider changes in optical path length, concentrations of HbO2 and Hb or degree of light scattering which takes place during such determination, comprising:(a) selecting electromagnetic radiation of at least three wavelengths to establish at least three selected wavelengths and wherein said at least three selected wavelengths includes a first wavelength which is a reference wavelength, a second wavelength which is a measuring wavelength and a third wavelength which is a measuring wavelength; (b) irradiating a selected location on said body part with light which at said location includes each of said selected wavelengths each of measured intensity; (c) measuring the light intensity and calculating the absorbance of each of said selected wavelengths after passing through said body part; (d) determining the differences between the absorption of light of said reference wavelength and said second and said third wavelengths by subtraction of the absorbance of said reference wavelength from that of said second and third wavelengths; (e) entering said differences of absorptions of the light of said reference wavelength and said second and third wavelengths in first and second equations derived from differences between relative in-situ determined isosbestic normalized extinction coefficients of Hb and HbO2 at said reference wavelength and said second and third wavelengths and solving said first and second equations for the amounts of HbO2 and Hb encountered as distinct from calculated concentrations; (f) continuously correcting said amounts for absorption contributions of cytochrome c oxidase to said percent oxygen saturation; and (g) determining tissue oxygen saturation percent as a ratio of the amount of HbO2 to the total amount of hemoglobin (HbO2+Hb) times 100.