Influence of shear rate on the optical properties of human blood in the spectral range 250 to 1100 nm

The intrinsic optical parameters-absorption coefficient mu(a), scattering coefficient mu(s), anisotropy factor g, and effective scattering coefficient mu'(s)-are determined for human red blood cells of hematocrit 42.1% dependent on the shear rate in the wavelength range 250 to 1100 nm. Integrating sphere measurements of light transmittance and reflectance in combination with inverse Monte-Carlo simulation are carried out for different wall shear rates between 0 and 1000 s(-1). Randomly oriented cells show maximal mu(a), mu(s), and mu'(s) values. Cell alignment and elongation, as well as the Fahraeus effect at increasing shear rates, lead to an asymptotical decrease of these values. The anisotropy factor shows this behavior only below 600 nm, dependent on absorption; above 600 nm, g is almost independent of shear rate. The decrease of mu's is inversely correlated with the hemoglobin absorption. Compared to randomly oriented cells, aggregation reduces all parameters by a different degree, depending on the hemoglobin absorption. It is possible to evaluate the influence of collective scattering phenomena, the absorption within the cell, and the cell shape. (C) 2007 Society of Photo-Optical Instrumentation Engineers.