Patent ID: 7333842

Claim:
A method for determining the oxygen saturation of blood in the presence of optical disturbance variables, particularly due to a biological tissue surrounding the blood vessel and/or the blood and/or the blood vessel itself comprising the steps of: generating spectral measurements (M i ) by transmission measurement and reflection measurement in a measurement spectrum at wavelengths that are isosbestic for hemoglobin (Hb) and oxyhemoglobin (HbO 2 ); generating at least one other measurement value (M a ) at a wavelength at which the reference values of hemoglobin and oxyhemoglobin differ; and comparing these measurements with known reference values of the reference spectra of hemoglobin and oxyhemoglobin; and further comprising the steps of: a) detecting at least two said spectral measurement values (M i1 , M i2 ) at wavelengths (λ i1 , λ i2 ) that are isosbestic for hemoglobin and oxyhemoglobin and at least the other measurement value (M a ) at a wavelength (λ a ) at which the reference values of hemoglobin and oxyhemoglobin differ as far as possible in the reference spectra in the measurement spectrum, wherein an auxiliary function (F H ) is generated at least from two of the measurement values (M i1 , M i2 ) for isosbestic wavelengths (λ i1 , λ i2 ); b) generating a reference function (F R ) in the reference spectra from the reference values (R i1 , R i2 ) corresponding to the at least two measurement values (M i1 , M i2 ) determined in the measurement spectrum for the same isosbestic wavelengths (λ i1 , λ i2 ) of hemoglobin and oxyhemoglobin, which reference function (F R ) is of the same type; c) generating a correction function (F K ) from the auxiliary function (F H ) of the measurement spectrum in which said at least two measurement values (M i1 , M i2 ) lie for isosbestic wavelengths (λ i1 , λ i2 ) and from the reference function (F R ) of the reference spectra in which the at least two reference values (R i1 , R i2 ) corresponding to the at least two measurement values (M i1 , M i2 ) lie, and generating a corrected auxiliary function (F Hk ) identical to the reference function (F R ) in the reference spectra in a corrected measurement spectrum by this correction function (F K ); and d) determining the oxygen saturation of the blood from the other measurement value (M a ″) converted to the corrected auxiliary function (F Hk ) of the corrected measurement spectrum in relation to the reference values for hemoglobin and oxyhemoglobin at this wavelength (λ a ).