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 the dehydration trial (Fig. 1), body mass in DEH was lower compared to control (75.8 ± 2.7 vs. 78.2 ± 2.7 kg, corresponding to a 3.1 ± 0.3% body mass loss, P < 0.01), and was restored in REH (77.7 ± 2.9 kg). DEH was accompanied by an increased arterial and venous haemoglobin concentration ([Hb]) (P < 0.01; Table 1), indicative of a reduction in blood volume, whereas REH restored these responses. Prior to exercise, intestinal and internal jugular venous temperatures were higher in DEH compared to control (38.3 ± 0.1 vs. 36.8 ± 0.1 and 37.7 ± 0.1 vs. 36.5 ± 0.1°C, respectively, both P < 0.001; Fig. 6C), but were restored to control values in REH (36.5–36.8°C). In DEH, both intestinal and blood temperature remained elevated and increased with work rates to a peak of 38.2 ± 0.1°C (P < 0.01; Fig. 6C). In control, intestinal and internal jugular venous temperature increased progressively to 37.4 ± 0.1 and 37.9 ± 0.1°C, with similar responses observed during REH. Mean skin temperature (Tsk) was unchanged across exercise intensities and between incremental conditions (33.8 ± 0.3, 32.6 ± 0.4 and 33.1 ± 0.3°C in control, DEH and REH, respectively). Heart rate followed the same pattern, with peak values being similar in all three conditions (179 ± 4, 184 ± 2 and 179 ± 3 beats min−1 in control, DEH and REH, respectively).
Affiliation: Centre for Sports Medicine and Human Performance, Brunel University, London, UK.