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.


OBJECTIVE
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 (CBFV(MEAN)) 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 CBFV(MEAN) decreased by 41 cm.s(-1) (pooled across conditions; all P < 0.0001). Absolute reductions of CBFV(MEAN) 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 CBFV(MEAN) (r = 0.37; P = 0.04).


CONCLUSIONS
Hyperventilation before lower-body resistance exercise exacerbates CBFV(MEAN) reductions during standing. Increased symptoms of orthostatic instability are associated with the magnitude of reductions in both MAP and CBFV(MEAN).
Romero
Steven A
SA
Laboratory for Applied Autonomic Neurophysiology, The University of Texas at San Antonio, San Antonio, TX, USA.
Cooke
William H
WH
D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001921:Brain / Q000098:blood supply*; D004244:Dizziness / Q000097:blood*; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000097:blood*; D008297:Male; D013781:Texas; D014891:Weight Lifting / Q000502:physiology*