Pulse oximetry: historical review and Ohmeda functional analysis.

Oximetry relies on the detection of the spectral properties of oxygenated and reduced hemoglobin. In vitro bench analysis capabilities have spurred the desire to accomplish accurate in vivo measurement through various techniques. The 1930-40s were a particularly active period for oximetry culminating in the development of pulse oximeters in the 1970s. Ohmeda pulse oximeters deal with the dynamics of this technology in several unique ways. Microprocessor controlled sequencing, signal processing and data validation schemes form the framework for accurate and stable readings. Arterial oxygen saturation readings are derived from the ratio of pulse-added signals of red and infrared light energy passed through tissue. Data manipulation that includes empirically derived constants produces numerical data that is clinically useful. A photo-plethysmographic waveform display of actual oximeter signal closes the loop between man and machine.