A pulse oximeter is a non-invasive electro-optical device for measuring both the heart rate and the degree to which the hemoglobin in one’s blood has been saturated with oxygen. This quantity is inferred by measuring the optical transmittance of perfused skin in different wavelengths of light. Red, green and infrared LEDs are convenient and common light sources. Blood oxygen saturation can be determined by comparing the values of Oxy-hemoglobin to Deoxy-hemoglobin. One method for doing this is by shining both a red LED and an infrared LED into a body part (such as a finger or wrist), and then measuring and comparing the relative intensities of the light from each LED in terms of a ratio. This ratio is then typically expressed as the percentage of oxygen saturation.
Pulse oximeter designs call for low power consumption and extensive analog and digital filtering. They are often implemented both as stand-alone medical and fitness devices as well as components of more comprehensive vital sign monitoring systems.