Studies on light reflection of blood in the application of fiber optics for dye-dilution curve.

The mechanism of light reflection in blood, which is the underlying principle for the use of fiber optics in in vivo densitometry or oximetry, was investigated theoretically and experimentally using bovine blood. The results are summarized as follows. 1) Theoretically, the intensity of light reflected, I, was represented by a formula: I=lo•~e-2KC•~[(1-P)•~r•~a, where I, 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. 2) Light reflection was proved to take place only in the region several microns apart from the tip of fiber optics. 3) Reflected light was increased with increase in hematocrit up 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 red blood cells. 4) a was calculated as 3.4%. Low reflexibility played a major part in decrement of in cident light.