Optical characteristics of flowing blood

The transmitted light strength (TS) through a thin blood layer changes with variation in blood flow, such as positive streaming transparency for low hematocrits and negative streaming transparency for high hematocrits. These phenomena are examined theoretically and experimentally. Maxwell’s equations are solved assuming that erythrocytes are oblate spheroids to investigate these phenomena due to flowing blood. The theoretical results reveal that the scattering and absorption cross sections for flowing blood are larger than those for stagnant blood. Experimental results indicate that the TS for both oxygenated and deoxygenated flowing blood, with a hematocrit of up to approximately 20%, was stronger than that for stagnant blood. The TS decreased for flowing blood with a hematocrit of approximately 20% or greater. Applying the theoretical scattering and absorption cross sections to the absorption and multiple scattering theory of Victor Twersky, the changes in the TS due to flowing blood are obtained theoretically. From the theoretical and experimental results, the positive streaming transparency phenomenon of flowing blood with a low hematocrit and the negative streaming transparency phenomenon with a high hematocrit are found to result from increased scattering and absorption cross sections because of the orientation of flowing erythrocytes.