Abstract
Living tissue is transparent to red and infrared radiation in the spectral range at which measurements of extinction coefficients of oxygenated and nonoxygenated blood are generally made. The extinction coefficient of nonhemolyzed blood in this region is much higher than that of the tissue. Incandescent lamps are cheap sources of these wavelengths, and photoconductive cells are extremely sensitive detectors. Therefore, if tissue is illuminated by light in this spectral region, one can expect to be able to detect the varying amount of blood in the tissue due to pulsating flow and vasomotor action. To convert changes in resistance of the photoconductive cells to voltages, simple electrical circuits had to be devised. Photocells and light-sources are built into one small unit which can be easily attached to any part of the body. Light passing through the tissue or scattered in it can be detected. Because of the high sensitivity of the cells, light filters can be used, and changes in flow due to venous or arterial blood can be studied. Experiments were performed in order to test the validity of the proposed method.
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