Effect of hyperoxia on oxygen consumption in exercising ponies.

Published reports of oxygen consumption (VO2) during exercise in hyperoxia are equivocal. By and large, when measured at the lung using respiratory gas equations, VO2 is elevated in hyperoxia and, when measured at the blood-tissue level using the cardiovascular Fick (CVF) equation, it is unchanged. We sought to provide some insight into this problem by making through the use of both equations simultaneous determinations of VO2 during hyperoxia in exercising ponies. In normoxia, during treadmill exercise (115 m/min, 10% grade) of seven ponies, there was no difference in exercise VO2, whether it was measured by the Haldane transformation (HT) or CVF equations (P greater than 0.05). In hyperoxia, the exercise VO2 was significantly increased from the normoxia condition (P less than 0.05) when measured by the HT equation but not when measured by the CVF equation (P greater than 0.05). By use of the CVF equation as the method of choice for VO2 determinations in hyperoxia, the present data show no change in exercise VO2 in the hyperoxic condition.