ABSTRACT
Photoplethysmography, and its more recent development light reflex rheography,7 have been widely used in the assessment of vascular disease. The photoelectric plethysmograph was first described in the 1930s,8,9 and was intended for use in the assessment of the arterial system. It was first applied to investigation of the venous system in 1978.10 The device assesses variation in the light absorption of the skin by hemoglobin in the dermal venous plexuses. When these are full during high venous pressure, the hemoglobin in the red blood cells absorbs light. As venous pressure falls, the venous plexuses become less full and light transmission increases. An example of a photoplethysmography transducer is shown in Figure 11.3.
