Hyperventilation before resistance exercise: Cerebral hemodynamics and orthostasis

Hyperventilation performed by athletes during preparation for resistance exercise might contribute to reports of postexercise orthostatic instability. PURPOSE: To test the hypothesis that post-resistance exercise orthostatic instability is associated with exaggerated reductions of cerebral blood-flow velocity after hyperventilation. METHODS: We recorded the ECG, end-tidal CO2, beat-by-beat finger arterial pressure, and cerebral blood-flow velocity in 10 healthy subjects. Subjects performed 10 repetitions of recumbent leg press using resistance equivalent to 80% of their six-repetition maximum during three separate trials (randomized): 1) no prior hyperventilation (NOHV); 2) after hyperventilation to an end-tidal CO2 of 3% (HV3%); and 3) after hyperventilation to an end-tidal CO2 of 2% (HV2%). After exercise, subjects stood upright for 10 s and rated symptoms of lightheadedness on a scale of 1 (none) to 5 (faint). RESULTS: Mean cerebral blood-flow velocity (CBFVMEAN) increased by 12% during exercise after NOHV and decreased by 14 and 25% during exercise after HV3% and HV2% (all P < 0.0001). During standing, mean arterial pressure (MAP) decreased by 96 mm Hg and CBFVMEAN decreased by 41 cm·s (pooled across conditions; all P < 0.0001). Absolute reductions of CBFVMEAN during standing were greater after HV2% compared with both NOHV and HV3% (P = 0.003). Ratings of perceived lightheadedness during standing increased with prior hyperventilation (P = 0.02) and correlated to the magnitude of reductions in MAP (r = 0.51; P = 0.003) and CBFVMEAN (r = 0.37; P = 0.04). CONCLUSIONS: Hyperventilation before lower-body resistance exercise exacerbates CBFVMEAN reductions during standing. Increased symptoms of orthostatic instability are associated with the magnitude of reductions in both MAP and CBFVMEAN.