Energy metabolism and circulation in dogs exercising in hypoxia.

Abstract

The interrelations between aerobic and anaerobic metabolic rates, O2 transport, and work performance were studied in dogs at rest and running on a treadmill with an incline of 10% at speeds varying from 4 to 16 km/hr, breathing 21, 15, or 11% O2-Measured were: O2 consumption, cardiac output (by the thermodilution method), heart rate, and lactic acid in blood. When air was breathed the O2 consumption increased up to the highest work level; but with decreased inspired O2, a maximum O2 uptake was reached, which was the lower and was attained at a lower work load, the lower the inspired O2. As the O2 consumption reached its maximum, anaerobic energy release, derived from lactate formation, set in. The behavior of the cardiac output and of the heart rate was similar to that of the O2 uptake, but their maximum values for each O2 level were reached at lower speeds.