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J Appl Physiol 86: 1534-1543, 1999;
8750-7587/99 $5.00
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Vol. 86, Issue 5, 1534-1543, May 1999

VCO2 and VE kinetics during moderate- and heavyintensity exercise after acetazolamide administration

Barry W. Scheuermann1, John M. Kowalchuk1,2, Donald H. Paterson1, and David A. Cunningham1,2

1 The Centre for Activity and Ageing, School of Kinesiology, and 2 Department of Physiology, The University of Western Ontario, London, Ontario, Canada N6A 3K7

The effect of carbonic anhydrase inhibition with acetazolamide (Acz) on CO2 output (VCO2) and ventilation (VE) kinetics was examined during moderate- and heavy-intensity exercise. Seven men [24 ± 1 (SE) yr] performed cycling exercise during control (Con) and Acz (10 mg/kg body wt iv) sessions. Each subject performed step transitions (6 min) in work rate from 0 to 100 W [below ventilatory threshold (<VET)] and to an O2 uptake corresponding to ~50% of the difference between the work rate at VET and peak O2 uptake [above ventilatory threshold (>VET)]. VE and gas exchange were measured breath by breath. The time constant (tau ) was determined for exercise <VET by using a single-exponential model (fit between 20 s and end-exercise); the mean response time (MRT) was determined for exercise >VET by using a three-component model (fit from the start of exercise). VCO2 kinetics were slower in Acz (<VET, tau  = 45 ± 6 s; >VET, MRT = 75 ± 10 s) than Con (<VET, tau  = 34 ± 6 s; >VET, MRT = 54 ± 7 s). During <VET exercise, VE kinetics were slower in Acz (tau  = 48 ± 6 s) than Con (tau  = 34 ± 6 s), but >VET kinetics were faster in Acz (MRT = 85 ± 17 s) than Con (MRT = 106 ± 16 s). Carbonic anhydrase inhibition slowed VCO2 kinetics during both moderate- and heavy-intensity exercise, demonstrating impaired CO2 elimination in the nonsteady state of exercise. The slowed VE kinetics in Acz during exercise <VET is consistent with a mechanism coupling VE kinetics with the flow of CO2 to the lungs.

control of breathing; carbonic anhydrase; end-tidal partial pressure of carbon dioxide; carbon dioxide output kinetics; ventilation kinetics


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