Reflection and Transmission of Light by Thin Films of Nonhaemolysed Blood

Abstract

The reflectance of light by nonhaemolysed blood has been studied previously only in thick layers. Some reflection oximetric techniques assumed an exponential relationship between oxygen saturation and reflection, whereas others assumed as inverse linear relationship. Reflectance and transmittance of thin films of flowing nonhaemolysed blood were measured, using an integrating sphere. Reflection and transmission were found to be linearly related, demonstrating that reflection is exponentially related to the extinction coefficient of haemoglobin. Confirmation was obtained of the observations that reflection increases and becomes asymptotic as sample depth increases and that reflection bears a parabolic relationship to the concentration of red blood cells.