Effects of heat and pressure on surface light reflectance at 660 and 880 nm

Presented is an analysis of changes in reflectance at the tissue surface resulting from heat-induced hyperemia and from applied pressure at the skin surface. Optical reflectance measurements are at wavelengths of 660 nm (red) and 880 nm (infrared). Human subject data consist of in vivo measurements from the calf of the leg. An index is calculated which is a logarithm of the ratio of reflected light intensity before and after stimulus application at each wavelength. The slope of the index curve, plotted as a function of source-detector separation, is related to the expected depth dependent physiological changes, in tissue blood fractional volume and tissue blood oxygen saturation