Pulse Oximeters

A pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood (as opposed to measuring oxygen saturation directly through a blood sample) and changes in blood volume in the skin, producing a photoplethysmograph.  Most monitors also display the heart rate.  Portable, battery-operated pulse oximeters are also available for home blood-oxygen monitoring.  The original oximeter was made by Millikan in the 1940s.  The precursor to today's modern pulse oximeter was developed in 1972, by Aoyagi at Nihon Kohden using the ratio of red to infrared light absorption of pulsating components at the measuring site.