The pulse oximeter is now a standard-of-care monitor. In its most basic form it measures the arterial oxygenation saturation. It accomplishes this through the use of the photoplethysmograph waveform (PPG) at two or more wavelengths. Advances in digital signal processing are allowing for a re-examination of these waveforms. It has been recognized for some time that the movement of venous blood can be detected (1, 2) using the PPG. For the most part, this phenomenon has been seen as a source of artifact which interferes with calculation of arterial saturation. On the other hand, if venous saturation can be reliably measured, interesting new possibilities are opened. We hypothesize that the PPG waveform, obtained non-invasively by modern pulse oximeters, can be analyzed via digital signal processing to infer the venous oxygen saturation
