V over dot CO2 and V over dot E kinetics during moderate- and heavy-intensity exercise after acetazolamide administration

The effect of carbonic anhydrase inhibition with acetazolamide (Acz) on CO2 output ((V)over dotCO(2)) and ventilation ((V)over dotE) kinetics was exam ined during moderate- and heavy-intensity exercise. Seven men [24 +/- 1 (SE ) yr] performed cycling exercise during control (Con) and Acz (10 mg/kg bod y wt iv) sessions. Each subject performed step transitions (6 min) in work rate from 0 to 100 W [below ventilatory threshold (<(V)over dotET)] and to an O-2 uptake corresponding to similar to 50% of the difference between the work rate at VET and peak O-2 uptake [above ventilatory threshold (>(V)ove r dotET)]. (V)over dotE and gas exchange were measured breath by breath. Th e time constant (tau) was determined for exercise <(V)over dotET by using a single-exponential model (fit between 20 s and end-exercise); the mean res ponse time (MRT) was determined for exercise > (V)over dotET by using a thr ee-component model (fit from the start of exercise). (V)over dotCO(2) kinet ics were slower in Acz (<(V)over dotET, tau = 45 +/- 6 s; >(V)ovr dotET, MR T = 75 +/- 10 s) than Con (<(V)over dotET, tau = 34 +/- 6 s; >(V)over dotET , MRT = 54 +/- 7 s). During <(V)over dotET exercise, (V)over dotE kinetics were slower in Act (tau = 48 +/- 6 s) than Con (tau = 34 +/- 6 s), but >(V) over dotET kinetics were faster in Act (MRT = 85 +/- 17 s) than Con (MRT = 106 +/- 16 s). Carbonic anhydrase inhibition slowed (V)over dotCO(2), kinet ics during both moderate- and heavy-intensity exercise, demonstrating impai red CO2 elimination in the nonsteady state of exercise. The slowed (V)ovr d otE kinetics in Acz during exercise <(V)over dotET is consistent with a mec hanism coupling (V)over dotE kinetics with the flow of CO2 to the lungs.