Changes in arterial blood gas tensions during unsteady-state exercise

Abstract

Arterial O2 (PaO2) and CO2 (PaCO2) tensions and inspired minute ventilation were measured during the first 2 min of stair-climbing exercise in 9 normal human subjects. The subjects climbed a staircase at a rate of approximately 9 m vertical height every minute, and arterial blood was drawn from an indwelling cannula at 15 s intervals. Large falls in PaO2 from a resting value of 92 .+-. 2.0 (mean .+-. SE) Torr to a lowest value of 65 .+-. 3.4 Torr were recorded in the first 50 s of exercise while PaCO2 oscillated around the resting value. Most subjects demonstrated an initial plateau of PaO2 for at least 7 s followed by a rapid fall and subsequent rise towards the resting level after 1 min. The falls in PaO2 measured were larger than those reported for laboratory exercise. The possible reasons for this discrepancy are discussed.