The Photoelectric Plethysmograph, is a finger sensor used to measure the rapidly occurring relative changes in pulse blood volume. This device utilizes a photosensitive cell to measure light reflected or passed through the tissue segment where the monitor is placed. The light source used produces a light in the infrared range (7000 to 9000 Angstroms). The light in this frequency is scattered by red blood cells so the amount of light reaching the photo sensor is related to the amount of blood through which it passed before reaching the sensor.
A clamp-like device houses both the light source and the sensor, and the assembly is placed on the finger or the thumb. It is cushioned with a soft rubber padding for added comfort and for reduction of movement artifacts.