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1Département de Kinésiologie, Université de Montréal, Montréal, Quebec, Canada; 2Institute of Sports and Preventive Medicine, University of Saarland, Saarbrucken, Germany; and 3Laboratoire de Physiopathologie de l'Exercice, HYLAB, Clinique du Mail, Grenoble, France
Submitted 17 May 2006 ; accepted in final form 28 August 2006
ABSTRACT
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 O2 consumption (
O2) but significantly (P < 0.05) increased arterial PCO2, plasma bicarbonate concentration, and respiratory exchange ratio (P < 0.05). At the three highest workloads, pulmonary ventilation (
E) and
E/
O2 were
510% lower (P < 0.05) when bicarbonate was infused than in the control situation, and hyperventilation was reduced by 1530%. These data suggest that the decrease in plasma pH is one of the factors that contribute to the hyperventilation observed at high workloads.
ventilatory threshold; lactate; acid-base balance; chemoreceptors
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