CHANGES IN OPTICAL-PROPERTIES OF HUMAN WHOLE-BLOOD IN-VITRO DUE TO SLOW HEATING

Optical properties of human whole blood were investigated in vitro at 633 nm using a double integrating sphere set-up, The blood flow was ma intained at a constant rate through a flow cell while continuously hea ting the blood at 0.2-1.1 degrees C/min from approximately 25 to 55 de grees C in a heat exchanger, A small, but rather abrupt decrease in th e scattering asymmetry factor (g-factor) of 1.7 +/- 0.6% and a similar increase in the scattering coefficient of 2.9 +/- 0.6% were observed at approximately 45-46 degrees C yielding an increase in the reduced s cattering coefficient of 40 +/- 10%. Furthermore, a continuous, manife st increase in the absorption coefficient was seen with increasing tem perature, on average 80 +/- 70% from 25 to 50 degrees C. The effect of the heating on the blood cells was also studied under a white-light t ransmission microscope, A sudden change in the shape of the red blood cells, from disc-shaped to spherical, was observed at approximately th e same temperature at which the distinct changes in g-factor and scatt ering coefficient were observed, i.e. at 45-46 degrees C, The results indicate that this shape transformation could explain the sudden chang e in scattering properties.