An Introduction to Pulse Oximeters: Equations and Theory

Pulse oximeters are electrical devices used for measuring blood oxygen saturation and pulse rate. Since their conception they have gained widespread acceptance in the medical community. This paper primarily focuses on the theory behind pulse oximetry. Beginning with the Beer-Lambert s Law, which relates the intensity of light before and after an absorbing medium, manipulations are made so that this law may be applied to a real time electrical system used for measuring blood oxygen saturation. When light is transmitted through a part of the human body the received signal is a small pulsation atop a baseline dc offset. The manipulations to the Beer-Lambert s law will result in an equation capable of using parameters from this received signal to compute the blood oxygen saturation. When this equation is used a long with the method described in this paper, the blood oxygen saturation may be computed to within 3% accuracy.