Optical Characteristics of Flowing Blood: Effects on the Pulse Oximeter

The causes of streaming transparency phenomena are discussed theoretically and experimentally in order to investigate the causes of the measurement error in pulse oximetry. We solve Maxwell equation under the assumption that erythrocytes are oblate spheroids to theoretically investigate the scattering phenomena due to erythrocytes. The theoretical results show that the forward scattering light strength for the flowing blood is much stronger than that for the resting blood. The streaming transparency phenomenon is caused by the light scattering change due to the orientation of erythrocytes. The scattering light intensity also strongly depends upon the wave-length of incident light.