Impact of aerobic fitness on cerebral blood flow and cerebral vascular responsiveness to CO₂ in young and older men

Abstract

We sought to test the hypothesis that brain blood flow and cerebral vascular responsiveness to carbon dioxide (CVR_CO2 ) are greater in aerobically trained young and old individuals compared to their untrained counterparts. In 11 young trained {[23 (20-26) years] [mean (95% confidence interval)]}, 10 young untrained [25 (22-28) years], 8 older trained [65 (61-69) years], and 9 older untrained [67 (64-71) years] healthy individuals, Doppler ultrasound of the internal carotid (ICA) and vertebral (VA) artery blood flow were determined, along with middle cerebral artery mean flow velocity (MCA V_mean ). Bilateral ICA blood flow was higher in trained individuals when compared to untrained (≈31%, P < 0.05), but was not influenced by age. VA blood flow was not affected by age or cardiorespiratory fitness. MCA V_mean was reduced with age [59.5 (55.0-64.1) cm/s young vs 43.6 (38.4-48.9) cm/s old, P < 0.05] with no significant effect of training observed. MCA CVR_CO₂ were not significantly affected by either age or training status, while ICA CVR_CO₂ tended to be elevated in the old trained group. These findings indicate that endurance training enhances bilateral ICA but not VA blood flow in both young and older individuals.