Photoelectric plethysmography is not new, but is a simple noninvasive technique to determine erythrocyte volume and oxygen saturation. The data are immediately available, accurate, repeatable, and recordable. Methods currently used for estimating microcirculation and oxygen saturation include clinical tests such as observation of skin color, temperature changes, capillary refill, and bleeding; chemical tests such as fluorscein injection; radioactive isotopes (24Na, 131I, 99mTc, and 133Xe); and instrumental methods (both invasive and noninvasive) such as temperature and infrared thermometry, thermocouples, oxygen probes, and/or the plethysmometer. None of these methods is entirely satisfactory.
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VANDEPUT et al. (1990) studied this question.