Fotopletysmografie

Fotopletysmografie, often abbreviated as PPG, is a non-invasive optical measurement technique that can be used to detect volumetric changes in blood within a part of the body. It works by emitting light from an LED onto the skin and measuring the amount of light that is reflected or transmitted back. The absorption of light is dependent on the amount of blood present in the tissue. As the heart pumps blood, the volume of blood in the capillaries changes, causing variations in light absorption. These variations are detected by a photodetector, which converts the light signal into an electrical signal.

The PPG signal typically consists of a pulsatile component, which corresponds to the arterial blood flow, and a non-pulsatile component, which is related to venous blood and other tissue properties. By analyzing the pulsatile component, it is possible to derive various physiological parameters. Commonly measured parameters include heart rate, which is determined by the frequency of the pulsatile signal, and oxygen saturation (SpO2), which is estimated by comparing the absorption of red and infrared light.

PPG sensors are small and inexpensive, making them ideal for wearable devices such as smartwatches and fitness trackers. They are also used in medical settings for continuous monitoring of vital signs, pulse oximetry, and in some research applications for assessing peripheral circulation. While PPG is a valuable tool, its accuracy can be affected by factors such as skin pigmentation, motion artifacts, ambient light, and the thickness of the tissue being measured.