Effect of low oxygen inhalation on changes in blood pH, lactate, and ammonia due to exercise

The present study examined the effect of hypoxia-induced respiratory alkalosis on exercise-induced metabolic acidosis and increases in plasma lactate and ammonia levels. Six male subjects underwent exercise of increasing intensity until exhaustion: (1) in normoxia (20.9% O₂) (=MAX), (2) in hypoxia (12% O₂) (=HP) in which hypoxic condition had been maintained from 60 min before to 30 min after exercise, and (3) the same intensity of exercise as HP in normoxia (=SUB). Arterialized blood was drawn from a superficial vein. Post-exercise blood pH was significantly higher in HP than in MAX (P<0.05), although plasma lactate was at the same level. For hypoxia as compared to normoxia, regression analysis confirmed a parallel shift of plasma lactate to higher pH levels indicating the effect of respiratory alkalosis (P<0.01). After exercise plasma levels of ammonia were lower in HP than in MAX (P<0.05). Regression analysis between ammonia and pH revealed nearly identical changes in hypoxia and normoxia at low pH. From these results, we conclude that: (1) hypoxia-induced respiratory alkalosis attenuated exhaustive exercise-induced metabolic acidosis, (2) plasma lactate concentration was determined by the relative exercise intensity, (3) the maximum plasma ammonia concentration under exhaustive exercise was reduced at hypoxia because of respiratory alkalosis.