The Effects of Hypoxia on Cerebral Blood Flow Velocity and Hemodynamics during Ergometer Bicycle Exercise

Abstract

The cerebral blood flow velocity (CBFV) response to acute hypoxia during exercise has been known to increase. But, how hemodynamics might respond to exercise in hypoxic condition and be associated with the change of CBFV remains unclear. PURPOSE: To determine the effects of hypoxia on CBFV and hemodynamics during bicycle ergometer exercise. METHODS: In a randomized, double-blind, crossover study, Twelve healthy volunteers (22.1±0.6yrs) were asked to perform the bicycle ergometer exercise three times in two hypoxic (3150m and 1900m altitudes) 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 corresponding to the altitudes of 3150m and 1900m was maintained using low oxygen gas mixture for the whole procedure of 40 minutes. CBFV in middle cerebral artery (MCA) were measured at rest 15 minutes, 5 and 10 minutes during exercise, 10 minutes recovery using transcranial-Doppler sonography. Non-invasive electrical cardiometry was used to obtain cardiac output (CO), thoracic fluid content (TFC) and flow time corrected (FTC). All data were analyzed using two-way ANOVA with repeated measures and Pearson’s correlation. RESULTS: CBFV in MCA in 3150m and 1900m was significantly higher than in control condition at 10 minutes during exercise (110±28 and 99±25 vs. 75±18 cm/s, p<.05). Heart rate (HR) in 3150m was significantly higher than in 1900m and control condition at 10 minutes during exercise (163±10 vs. 154±6 and 152±8 bpm, p<05). TFC in 3150m and 1900m was significantly lower than in control condition at 10 minutes during exercise (27±1 and 26±1 vs. 30±2, p<.05). FTC in 3150m and 1900m was significantly lower than in control condition at 10 minutes during exercise (240±20 and 254±16 vs. 265±18 ms, p<.05). However, CO and stroke volume (SV) were not significant different between three conditions. CONCLUSIONS: These results suggest that exercise in normobaric hypoxic condition might increase CBFV, which might be independent of hemodynamic changes.