ON THE DETERMINATION OF THE PHYSIOLOGICALLY EFFECTIVE PRESSURES OF OXYGEN AND CARBON DIOXIDE IN ALVEOLAR AIR

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Abstract
Because the limitations inherent in direct methods for sampling alveolar air become critical in expts. on exercising subjects, an indirect method has been devised for calculating alveolar gas pressures which requires simply the detn. of arterial pCO2 and the pCO2 and pO2 of inspired and expired air. A theoretical analysis indicates that alveolar pressures so detd. represent the physiologically effective mean pressures and are not subject to errors introduced by "space" and "time" factors. An experimental comparison of this method with the Haldane-Priestley sampling method indicates that although the discrepancies are minor at rest, during exercise the alveolar pressures detd. by the H-P method yield values for pCO2 which average 12.7 mm. Hg too high and values for alv. pO2 which average 18.5 mm. Hg too low.