Bicarbonate infusion and pH clamp moderately reduce hyperventilation during ramp exercise in humans

To test the hypothesis that the decrease in plasma pH contributes to the hyperventilation observed in humans in response to exercise at high workloads, five healthy male subjects performed a ramp exercise [ maximal workload: 352 W (SD 35)] in a control situation and when arterialized plasma pH was maintained at the resting level ( pH clamp) by intravenous infusion of sodium bicarbonate [129 mmol (SD 23), beginning at 59% maximal workload (SD 5)]. Bicarbonate infusion did not modify O-2 consumption (V O-2) but significantly (P < 0.05) increased arterial P CO2, plasma bicarbonate concentration, and respiratory exchange ratio (P < 0.05). At the three highest workloads, pulmonary ventilation (V (E)) and V (E)/V O-2 were similar to 5 - 10% lower (P < 0.05) when bicarbonate was infused than in the control situation, and hyperventilation was reduced by 15 - 30%. These data suggest that the decrease in plasma pH is one of the factors that contribute to the hyperventilation observed at high workloads.