V˙co 2 andV˙e kinetics during moderate- and heavyintensity exercise after acetazolamide administration

Abstract

The effect of carbonic anhydrase inhibition with acetazolamide (Acz) on CO2 output (V˙co 2) and ventilation (V˙e) 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 (<V˙eT)] and to an O2 uptake corresponding to ∼50% of the difference between the work rate atV˙eT and peak O2 uptake [above ventilatory threshold (>V˙eT)].V˙e and gas exchange were measured breath by breath. The time constant (τ) was determined for exercise <V˙eT by using a single-exponential model (fit between 20 s and end-exercise); the mean response time (MRT) was determined for exercise >V˙eT by using a three-component model (fit from the start of exercise).V˙co 2 kinetics were slower in Acz (<V˙eT, τ = 45 ± 6 s; >V˙eT, MRT = 75 ± 10 s) than Con (<V˙eT, τ = 34 ± 6 s; >V˙eT, MRT = 54 ± 7 s). During <V˙eT exercise,V˙e kinetics were slower in Acz (τ = 48 ± 6 s) than Con (τ = 34 ± 6 s), but >V˙eT kinetics were faster in Acz (MRT = 85 ± 17 s) than Con (MRT = 106 ± 16 s). Carbonic anhydrase inhibition slowedV˙co 2 kinetics during both moderate- and heavy-intensity exercise, demonstrating impaired CO2 elimination in the nonsteady state of exercise. The slowedV˙e kinetics in Acz during exercise <V˙eT is consistent with a mechanism coupling V˙e kinetics with the flow of CO2 to the lungs.