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Abstract

Method and apparatus for spectrophotometrically determining the concentration of a number of hemoglobin derivatives comprising at least deoxyhemoglobin and oxyhemoglobin or parameters derived from the concentration of individual hemoglobin derivatives, in particular the oxygen saturation fraction, in whole blood, in which light is transmitted to the blood under test, the modification on the light transmitted to the blood which the blood causes is determined at a number of individual wavelengths, and the concentrations (or the derived parameters) are determined on the basis of the light modification at the individual wavelengths and on the basis of predetermined coefficients representing the light absorption characteristics of each of the hemoglobin derivatives at each of the individual wavelengths, any error on the determination values due to turbidity being substantially compensated for by utilizing predetermined coefficients representing an absorption characteristic of turbidity at each of the wavelengths. The measurement is normally performed at a number of wavelengths which is at least equal to the number of hemoglobin derivatives to be determined plus one. Although the turbidity-caused contribution to the total reduction in the light transmission is not based on any direct proportionality between the reduction in light transmission and the concentration of the turbidity-causing components (such as is the case with the hemoglobin derivatives), the 'absorbances' caused by the turbidity at each particular wavelength may simply be eliminated from the equation set from which the concentrations of the hemoglobin derivatives are calculated.

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