Effect of hypercapnia on changes in blood pH, plasma lactate and ammonia due to exercise

The present study examined the effects of hypercapnia on changes in blood pH, plasma lactate and ammonia due to exhaustive exercise. Six male subjects underwent exercise of increasing intensity until exhaustion: (1) breathing air = MAX (maximal exercise), or (2) under hypercapnia (HC: 21% O₂, 6% CO₂) that had been maintained from 60 min before to 30 min after exercise = HC; and (3) exercise of the same intensity as HC in air = SUB (submaximal exercise). Arterialized blood was drawn from a superficial vein. Blood pH in HC was significantly lower than in MAX or SUB at rest, at the end of exercise and throughout recovery (P<0.05). Plasma lactate and ammonia concentration in HC was significantly lower than in MAX (P<0.05), and similar to that in SUB at the end of exercise and throughout recovery. Respiratory acidosis resulting from hypercapnia shifted the linear lactate to blood pH relationship during exhaustive exercise below that at normocapnia (P<0.001). The reduced slope of linear blood pH to ammonia relationship under hypercapnia (P<0.001) is attributed to lactic acidosis that is less, due to the lesser work intensity at the end of exhaustion, than that of normocapnia. From these results we conclude that (1) hypercapnia-induced respiratory acidosis promoted the decrease in blood pH due to lactate production throughout recovery; (2) plasma lactate concentration at maximal exercise was lowered under hypercapnia; (3) plasma ammonia concentration at maximal exercise was reduced, probably due to a less intense lactic acidosis.