Photoplethysmography (PPG) is a non-invasive, optical measurement that may be used to detect changes in blood volume within tissue, such as skin, of an individual. PPG may be used with pulse oximeters, vascular diagnostics, and digital blood pressure detection systems. Typically, a PPG system includes a light source that is used to illuminate tissue of a patient. A photodetector is then used to measure small variations in light intensity associated with blood volume changes proximal to the illuminated tissue.
In general, a PPG signal is a physiological signal that includes an AC physiological component related to cardiac synchronous changes in the blood volume with each heartbeat. The AC component is typically superimposed on a DC baseline that may be related to respiration, sympathetic nervous system activity, and thermoregulation.