Dehydration affects cerebral blood flow but not its metabolic rate for oxygen during maximal exercise in trained humans.
Bottom Line: In all conditions, reductions in ICA and MCA Vmean were associated with declining cerebral vascular conductance, increasing jugular venous noradrenaline, and falling arterial carbon dioxide tension (P aCO 2) (R(2) ≥ 0.41, P ≤ 0.01) whereas CCA flow and conductance were related to elevated blood temperature.In conclusion, dehydration accelerated the decline in CBF by decreasing P aCO 2 and enhancing vasoconstrictor activity.However, the circulatory strain on the human brain during maximal exercise does not compromise CMRO2 because of compensatory increases in O2 extraction.
Affiliation: Centre for Sports Medicine and Human Performance, Brunel University, London, UK.Show MeSH
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Mentions: In control in the dehydration trial, ICA blood flow and MCA Vmean increased by ∼17 ± 2% from rest to submaximal exercise and thereafter declined to resting values (both P < 0.05; Fig. 3A and D). Conversely, during DEH, ICA blood flow did not increase from rest to moderate exercise, but declined to below resting values at WRmax (−11% vs. rest, P < 0.05). ICA blood flow responses to REH were similar to control. In all conditions, the decline in blood flow at high exercise intensities was associated with reductions in vessel diameter and blood velocity. In contrast to ICA blood flow, CCA blood flow did not change during low intensity exercise in control, but increased progressively with further increases in exercise intensity (rest = 0.47 ± 0.02 vs. 0.60 ± 0.02 l min−1, P < 0.01) (Fig. 3C). During DEH, CCA blood flow was elevated (P < 0.05) at the start of exercise and did not change throughout incremental exercise. CCA blood flow responses to REH incremental exercise were similar to control. The increases in CCA blood flow in control and REH were associated with increases in blood velocity (P < 0.05). In the euhydration trial, ICA and CCA blood flow, and MCA Vmean were similar at rest and during incremental exercise.
Affiliation: Centre for Sports Medicine and Human Performance, Brunel University, London, UK.