Normoxic and acute hypoxic exercise tolerance in man following acetazolamide
Stager, J.M.; Tucker, A.; Cordain, L.; Engebretsen, B.J.; Brechue, W.F.; Matulich, C.C.
Medicine and Science in Sports and Exercise 22(2): 178-184
1990
ISSN/ISBN: 0195-9131 PMID: 2355814 Document Number: 353007
The influence of acetazolamide (ACZ) upon the ability to perform and sustain maximal and submaximal exercise bouts under normoxic and hypoxic conditions was examined in four groups of healthy male subjects (N = 27). ACZ (500 mg) or inert placebo (Pla) was administered prior to exercise in a quasi-randomized, double-blind, cross-over fashion. ACZ was shown to lower venous pH (ACZ, 7.31 .+-. 0.01, vs Pla, 7.35 .+-. 0.08) and bicarbonate (ACZ, 22.4 .+-. 0.27 mM, vs Pla, 25.4 .+-. 0.6 mM) and to elevate urine pH (ACZ, 7.36 .+-. 0.06, vs Pla, 5.84 .+-. 0.19) and tended to elevate .ovrhdot.VE (P = 0.07) at rest. Peak .ovrhdot.VO2 measured using a continuous incremental protocol was unaltered in normoxia, while peak .ovrhdot.VCO2 and RER were lowered by ACZ. No significant effect of ACZ upon .ovrhdot.VO2, .ovrhdot.VCO2, RER, or heart rate (HR) was observed during submaximal exercise (75% of peak .ovrhdot.VO2) although .ovrhdot.VE was increased by 14% and time to exhaustion (EXHt) was reduced by 29%. During acute hypoxia at a simulated altitude of 4,270 m (Pbar = 446 mm Hg), no significant differences were noted in .ovrhdot.VE, .ovrhdot.VO2, .ovrhdot.VCO2, RER, HR, or arterial saturation (SaO2) at rest. Prior to exercise, venous pH (ACZ, 7.39 .+-. 0.04, vs Pla, 7.44 .+-. 0.007) and bicarbonate were lower with ACZ (ACZ, 21.6 .+-. 0.46 mM, vs Pla, 24.2 .+-. 0.25 mM), while urine pH was higher (ACZ, 7.6 .+-. 0.07, vs Pla, 5.9 .+-. 0.25). Other than a higher PCO2 and lower venous lactate with ACZ, no significant differences were identified at peak .ovrhdot.VO2. Although ACZ reduced EXHt during hypoxic submaximal exercise by 26%, no differences were observed in .ovrhdot.VE, .ovrhdot.VO2, .ovrhdot.VCO2, HR, or SaO2. These data suggest that ACZ has a dramatic effect upon the ability to sustain submaximal exercise while having little influence upon aspects of maximal exercise. The mechanism(s) by which ACZ limits submaximal exercise tolerance is/are unclear; however, we hypothesize that they are associated either with disturbances in acid-base status or with the well known diuretic effects of ACZ.