M. Bergerud, J. Kepple, C. Cozza, L. Howard, D.B. Thorp

Gonzaga University, Spokane, WA

Cardiorespiratory responses influence the fast component of oxygen uptake (VO2) kinetics. Previous research has shown that acute hypoxia results in increased heart rate (HR) and minute ventilation (VE) while keeping VO2 constant. PURPOSE: The goal of this study was to elicit increased HR and VEwith acute exposure to hypoxia prior to the onset of moderate intensity exercise to determine whether this ‘hypoxic priming’ would affect the oxygen deficit (OD) and the fast component of VO2 kinetics as measured by time to reach steady-state VO2(Tss). METHODS: Subjects (n=9 [3 female, 6 male], age 18-21) completed four trials of cycling on a bicycle ergometer. Each trial began with a priming protocol, consisting of 4 min. of cycling at 30W inspring hypoxic (10.01% O2) or normoxic air, followed by 1 min. of breathing normoxic air at 30W. The priming protocol was followed immediately by 5 min. of cycling at 100W inspiring normoxic air for all trials. The completion of the priming and experimental protocol in series constituted one trial. Each subject completed 2 trials under the normoxic priming condition and 2 trials under the normoxic priming condition in a randomized order. VE, VO2, HR, and arterial oxygen saturation were measured throughout all trials using a metabolic cart, wireless HR monitor and pulse oximeter. OD was calculated using a Riemann Sum method at the onset of 100W exercise. Within subjects, OD and Tssfrom both hypoxic and both normoxic trials were averaged. The hypoxic and normoxic conditions were then compared using dependent t-tests. RESULTS:No significant differences were detected for OD and Tssbetween hypoxic and normoxic priming conditions (OD: 0.39±0.17 vs. 0.56±0.22 L, p=0.075; Tss: 84.0±27.6 vs. 112.2±30.6 s p=0.121). HR (123.24±13.71 vs. 106.76±15.35 bpm, p<0.01) and VE(24.18±5.49 vs. 17.38±2.87 L.min-1, p<0.01) were significantly elevated during the hypoxic priming exercise compared to normoxia, while VO2was significantly reduced during the hypoxic priming exercise (0.708±0.251 vs. 0.928±0.210 L.min-1, p<0.01). There was no difference in HR, VEor VO2between conditions during 100W normoxic cycling. CONCLUSION:Despite elevated HR and VE, acute hypoxia exposure during prior light exercise did not affect the fast component of VO2kinetics in subsequent moderate intensity exercise.

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