Development of a mathematical model for the transmission of visible light in unhemolysed whole blood

A new theoretical model was derived describing the multiple scattering and absorption of unhemolysed whole blood and taking for the first time the sieve effect into account. The influence of the physiological parameters hematocrit and cell or aggregate size as well as the analytical parameters pathlength and detector aperture were examined. The following results were obtained: 1) The model was able to fit experimental data where Loewinger's model failed to, which shows the validity of the new model. 2) The formula describing the sieve effect was demonstrated by simulation and confirmed experimentally by eliminating scattering. 3) The duality of areas of the detector and illuminated sample was demonstrated for the calculation of the scattered light yield (q). 4) The dynamic behavior of whole blood transmission was identified as an aggregation effect of the red blood cells when flow stops. 5) The scattering coefficient of whole blood is a function of the hemoglobin composition of the red blood cells. Despite the fact that the model could not enable the determination of the different hemoglobin derivatives needed for CO=oximetry, the model gave a deeper and new insight in the physiological and analytical factors influencing the light transmission of unhemolysed whole blood.