Origin of Photoplethysmographic Waveform at Green Light

In this article we analyze a number of observations obtained with the reflection-mode photoplethysmography (PPG), which can hardly be explained by commonly accepted model of the PPG-signal formation. It is shown that the physiologic model of light interaction with living tissue recently proposed by our group provides reasonable explanation of all observations. According to this model, it is pulsatile transmural pressure of the arteries, which compresses/decompresses the density of capillaries in the dermis, thus modulating the blood volume in the capillary bed, which in its turn modulates the power of remitted green light.