Cerebral Blood Flow Velocity and EEG Response during Ergometer Exercise in Normoxia and Hypoxia

Abstract

The cerebral blood flow velocity (CBFV) response to acute hypoxia has been known to increase. But, how CBFV might respond to exercise in hypoxic condition and be associated with EEG remains unclear. PURPOSE: To evaluate the effects of exercise in hypoxic condition corresponding to the altitudes of 4000m on cerebral blood flow velocity and EEG. METHODS: In a randomized, double-blind, balanced crossover study, ten healthy volunteers (19.8±0.4yrs) were asked to perform the incremental bicycle ergometer exercise twice in hypoxic and control(sea level) condition with a week interval, respectively. Exercise intensity was set initially at 50W and increased by 25W every 2 minutes to 125W. Acute normobaric hypoxic condition was maintained for 45 minutes using low oxygen gas mixture. CBFV in middle cerebral artery (MCA) and EEG were measured at rest 5 minutes, rest 15 minutes, immediately after exercise, and 15 minutes recovery using transcranial-Doppler sonography and EEG signal was recorded from 6 scalp sites leading to analysis of alpha and beta wave relative activities. All data were analyzed using two-way ANOVA with repeated measures and Pearson’s correlation. RESULTS: CBFV in MCA in hypoxic condition was significantly higher than in control condition at rest 5 minutes (83±9 vs. 69±9 cm/s, p<.01), rest 15 minutes (87±8 vs. 67±7 cm/s, p<.001), immediately after exercise (112±9 vs. 97±9 cm/s, p<.01), and 15 minutes recovery (91±11 vs. 74±7 cm/s, p<.01). However, no significant correlation was found between the changes of CBFV and EEG wave activities. CONCLUSION: These results suggest that hypoxia might amply the changes of CBFV observed during exercise. But, the changes of CBFV might have no association with the changes of EEG wave activities in hypoxia.