The principle is based on the measurement of subtle changes in light reflected from the skin. Small motions of the body, due to the mechanical flow of blood provide complementary cardiac and blood oxygen information. The principle itself has been known to Health Sciences for over 80 years and is similar to pulse oximeters. With AI developments and improved technology greater analysis is now possible and the underlying tool set is used by hundreds of institutions around the world.
Photoplethysmography (PPG) is a simple and inexpensive contact based measurement.
It is a non-invasive technology that uses a light source and a photodetector at the surface of skin to measure the volumetric variations of blood circulation.
Remote Photoplethysmography (RPPG) is based on the same principles as PPG but is a contactless measurement.
It measures the variance of red, green, and blue light reflection changes from the skin, as the contrast between specular reflection and diffused reflection.