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Title: Dehydration affects cerebral blood flow but not its metabolic rate for oxygen during maximal exercise in trained humans
Authors: Trangmar, SJ
Chiesa, ST
Stock, CG
Kalsi, KK
Secher, NH
González-Alonso, J
Keywords: Dehydration;Systemic and locomotor muscle blood flow;Cerebral blood flow (CBF)
Issue Date: 2014
Publisher: Blackwell Publishing Ltd
Citation: Journal of Physiology, 592:14, pp. 3143 - 3160, 2014
Abstract: Key points: Dehydration accrued during exercise in the heat challenges systemic and locomotor muscle blood flow, but its impact on cerebral blood flow (CBF) and metabolism remains unknown. This study assessed whether dehydration compromises CBF and the cerebral metabolic rate for oxygen (CMRO2) during incremental exercise to exhaustion in trained males. Dehydration induced an early reduction in CBF during progressive exercise, but increased O2 extraction secured CMRO2. In all hydration conditions declining CBF at high exercise intensities was correlated to decreasing arterial carbon dioxide tension and increasing jugular venous plasma noradrenaline. These results suggest that dehydration impairs CBF at high exercise intensities, but this circulatory strain on the human brain does not compromise CMRO2. Intense exercise is associated with a reduction in cerebral blood flow (CBF), but regulation of CBF during strenuous exercise in the heat with dehydration is unclear. We assessed internal (ICA) and common carotid artery (CCA) haemodynamics (indicative of CBF and extra-cranial blood flow), middle cerebral artery velocity (MCA Vmean), arterial-venous differences and blood temperature in 10 trained males during incremental cycling to exhaustion in the heat (35°C) in control, dehydrated and rehydrated states. Dehydration reduced body mass (75.8 ± 3 vs. 78.2 ± 3 kg), increased internal temperature (38.3 ± 0.1 vs. 36.8 ± 0.1°C), impaired exercise capacity (269 ± 11 vs. 336 ± 14 W), and lowered ICA and MCA Vmean by 12-23% without compromising CCA blood flow. During euhydrated incremental exercise on a separate day, however, exercise capacity and ICA, MCA Vmean and CCA dynamics were preserved. The fast decline in cerebral perfusion with dehydration was accompanied by increased O2 extraction (P < 0.05), resulting in a maintained cerebral metabolic rate for oxygen (CMRO2). 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) (R2 ≥ 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. © 2014 The Authors.
Description: This article has been made available through the Brunel Open Access Publishing Fund.
ISSN: 1469-7793
Appears in Collections:Sport
Brunel OA Publishing Fund
Dept of Life Sciences Research Papers

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