NDLI: Dehydration affects cerebral blood flow but not its metabolic rate for oxygen during maximal exercise in trained humans

Content Provider	PubMed Central
Author	Trangmar, Steven J. Chiesa, Scott T. Stock, Christopher G. Kalsi, Kameljit K. Secher, Niels H. José, González-alonso
Copyright Year	2014
Abstract	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 V mean), 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 V mean by 12–23% without compromising CCA blood flow. During euhydrated incremental exercise on a separate day, however, exercise capacity and ICA, MCA V mean 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 V mean were associated with declining cerebral vascular conductance, increasing jugular venous noradrenaline, and falling arterial carbon dioxide tension ( ) (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 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.
Related Links	http://dx.doi.org/10.1113/jphysiol.2014.272104
Ending Page	3160
Page Count	18
Starting Page	3143
File Format	PDF
ISSN	00223751
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 14
Volume Number	592
Language	English
Publisher	Blackwell Science Inc
Publisher Date	2014-07-15
Access Restriction	Open
Rights Holder	Blackwell Science Inc
Subject Keyword	Physiology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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