[Validity of calculating oxygen saturation at rest and during exercise]

Oxygen saturation calculated with the formulae proposed by Heck, Kelman, Lutz, Marsoner, Severing-haus and Siggaard-Andersen, was compared with oxygen saturation measured photometrically. An analysis of 1350 peripheral venous, mixed venous and arterial blood samples obtained during bicycle ergometry revealed that only the calculations using the Kelman, Siggaard-Andersen and Severing-haus formulae had adequate validity and reliability over a wide measuring range. If, however, the oxygen saturation figures are to be used for further calculations, direct measurement should be given preference to avoid errors (for example, in shunt calculation).