Studies on Light Reflection of Blood in the Application of Fiber Optics

Abstract

The mechanism of light reflection in blood, which is the underlying principle for the use of fiber optics in in vivo densitometry or oxi-metry, was investigated theoretically and experimentally using bovine blood. Theoretically, the intensity of light reflected, I, was represented by a formula: I=I0xe-2KCx[(1-p)/p]xrxa, where I0, K, C, p, and a were incident light, extinction coefficient of plasma, hematocrit and reflexibility of blood, respectively; r is the length of the side of a cube when the red blood cell was assumed as of cubic form. Light reflection took place only in the region several microns apart from the tip of fiber optics. Reflected light was increased with increase in hematocritup to 60% but was decreased with further increase in hematocrit. This phenomenon was interpreted as being due to so-called "shading effect" resulting from rescattering of reflected light by redbloodcells. The a value was calculated as 3.4%. Low reflexibility played a major part in decrement of incident light.