Pulse plethysmography derived noninvasive measures of volume replacement.

摘要

Photo-electric plethysmography (pleth) is far from new. The underlying principles were first described in 1938. Pleth has been associated with blood volume changes in peripheral vascular beds and postulated to predict or reflect hemodynamic changes, including blood pressure. The basic principles involve emitting light from a source and using a photodetector to measure either reflected (as applied in a forehead sensor) or transmitted (as in a finger sensor) light, depending on receiver positioning. The measured light intensity is impacted by both constant factors such as absorption by skin, muscle, and bone, and variable factors, including the differing amounts of blood present in the tissue based on timing of the cardiac cycle, temperature, and blood-borne factors. Although the increased amount of peripheral blood occurring in systole results in only small increases in light absorption, these signals can be amplified and displayed as a plethysmogram.