Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism

Trangmar, Steven J.; Chiesa, Scott T; Llodio, Inaki; García, Benjamin A.; Kalsi, Kameljit; Secher, Niels H.; González‐Alonso, José

doi:10.1152/ajpheart.00525.2015

Cited by 51 publications

(62 citation statements)

References 50 publications

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“…For example, Nybo et al (2002a) reported that CMRO 2 is ß7% higher during 'hyperthermic' exercise when core temperature was ß1.6°C higher than control -suggesting a Q10 of ß1.5. Conversely, Trangmar et al (2014Trangmar et al ( , 2015 reported no change in CMRO 2 during exhaustive exercise, even when core temperature was further elevated as a result of dehydration.…”

Section: Introductionmentioning

confidence: 91%

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Cerebral metabolism, oxidation and inflammation in severe passive hyperthermia with and without respiratory alkalosis

Bain

Hoiland

Donnelly

et al. 2020

The Journal of Physiology

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Key points It was unknown whether respiratory alkalosis impacts the global cerebral metabolic response as well as the cerebral pro‐oxidation and inflammatory response in passive hyperthermia. This study demonstrated that the cerebral metabolic rate was increased by ∼20% with passive hyperthermia of up to +2°C oesophageal temperature, and this response was unaffected by respiratory alkalosis. Additionally, the increase in cerebral metabolism did not significantly impact the net cerebral release of oxidative and inflammatory markers. These data indicate that passive heating of up to +2°C core temperature in healthy young men is not enough to confer a major oxidative and inflammatory burden on the brain, but it does markedly increase the cerebral metabolic rate, independently of PnormalaCO2. Abstract There is limited information concerning the impact of arterial PnormalCO2/pH on heat‐induced alteration in cerebral metabolism, as well as on the cerebral oxidative/inflammatory burden of hyperthermia. Accordingly, we sought to address two hypotheses: (1) passive hyperthermia will increase the cerebral metabolic rate of oxygen (CMRO2) consistent with a combined influence of Q10 and respiratory alkalosis; and (2) the net cerebral release of pro‐oxidative and pro‐inflammatory markers will be elevated in hyperthermia, particularly in poikilocapnic hyperthermia. Healthy young men (n = 6) underwent passive heating until an oesophageal temperature of 2°C above resting was reached. At 0.5°C increments in core temperature, CMRO2 was calculated from the product of cerebral blood flow (ultrasound) and the radial artery–jugular venous oxygen content difference (cannulation). Net cerebral glucose/lactate exchange, and biomarkers of oxidative and inflammatory stress were also measured. At +2.0°C oesophageal temperature, arterial PnormalCO2 was restored to normothermic values using end‐tidal forcing. The primary findings were: (1) while CMRO2 was increased (P < 0.05) by ∼20% with hyperthermia of +1.5–2.0°C, this was not influenced by respiratory alkalosis, and (2) although biomarkers of pro‐oxidation and pro‐inflammation were systemically elevated in hyperthermia (P < 0.05), there were no differences in the trans‐cerebral exchange kinetics. These novel data indicate that passive heating of up to +2°C core temperature in healthy young men is not enough to confer a major oxidative and inflammatory burden on the brain, despite it markedly increasing CMRO2, irrespective of arterial pH.

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Section: Introductionmentioning

confidence: 91%

“…Conversely, Trangmar et al . (, ) reported no change in CMRO 2 during exhaustive exercise, even when core temperature was further elevated as a result of dehydration.…”

Section: Introductionmentioning

confidence: 95%

Cerebral metabolism, oxidation and inflammation in severe passive hyperthermia with and without respiratory alkalosis

Bain

Hoiland

Donnelly

et al. 2020

The Journal of Physiology

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“…4). Haemoconcentration during heat stress is sometimes interpreted to indicate some level of dehydration, which has been shown to potentiate reductions in CBF and CDO 2 (Trangmar et al 2014(Trangmar et al , 2015. Additionally, the haemoconcentration that occurred with both cooling and heating caused an increase in blood viscosity (Table 1), which would be expected to compromise CBF according to Poiseuille's Law (Nichols et al 1974).…”

Section: Factors Contributing To Cdo 2 During Isolated Thermal Strainmentioning

confidence: 99%

“…Some reports show cognitive impairments with acute and prolonged hypoxia despite global CDO 2 and CMRO 2 being maintained, a conundrum that might be partly explained by regional reductions in CBF that become more pronounced with continued hypoxic exposure (Lawley et al 2017). Severe heat stress causes large decreases in CDO 2 but CMRO 2 is maintained or even increased and cognitive impairments are observed only when the task complexity is maximised (Nybo et al 2002b;Trangmar et al 2015;Piil et al 2017). Whole body cooling decreases both central and peripheral nerve conduction velocity and has been shown to slow central information processing (Rammsayer et al 1995).…”

Section: Introductionmentioning

confidence: 99%

Global REACH 2018: The influence of acute and chronic hypoxia on cerebral haemodynamics and related functional outcomes during cold and heat stress

Gibbons

Tymko

Thomas

et al. 2020

The Journal of Physiology

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Key points Thermal and hypoxic stress commonly coexist in environmental, occupational and clinical settings, yet how the brain tolerates these multi‐stressor environments is unknown Core cooling by 1.0°C reduced cerebral blood flow (CBF) by 20–30% and cerebral oxygen delivery (CDO2) by 12–19% at sea level and high altitude, whereas core heating by 1.5°C did not reliably reduce CBF or CDO2 Oxygen content in arterial blood was fully restored with acclimatisation to 4330 m, but concurrent cold stress reduced CBF and CDO2 Gross indices of cognition were not impaired by any combination of thermal and hypoxic stress despite large reductions in CDO2 Chronic hypoxia renders the brain susceptible to large reductions in oxygen delivery with concurrent cold stress, which might make monitoring core temperature more important in this context Abstract Real‐world settings are composed of multiple environmental stressors, yet the majority of research in environmental physiology investigates these stressors in isolation. The brain is central in both behavioural and physiological responses to threatening stimuli and, given its tight metabolic and haemodynamic requirements, is particularly susceptible to environmental stress. We measured cerebral blood flow (CBF, duplex ultrasound), cerebral oxygen delivery (CDO2), oesophageal temperature, and arterial blood gases during exposure to three commonly experienced environmental stressors – heat, cold and hypoxia – in isolation, and in combination. Twelve healthy male subjects (27 ± 11 years) underwent core cooling by 1.0°C and core heating by 1.5°C in randomised order at sea level; acute hypoxia (PET,O2 = 50 mm Hg) was imposed at baseline and at each thermal extreme. Core cooling and heating protocols were repeated after 16 ± 4 days residing at 4330 m to investigate any interactions with high altitude acclimatisation. Cold stress decreased CBF by 20–30% and CDO2 by 12–19% (both P < 0.01) irrespective of altitude, whereas heating did not reliably change either CBF or CDO2 (both P > 0.08). The increases in CBF with acute hypoxia during thermal stress were appropriate to maintain CDO2 at normothermic, normoxic values. Reaction time was faster and slower by 6–9% with heating and cooling, respectively (both P < 0.01), but central (brain) processes were not impaired by any combination of environmental stressors. These findings highlight the powerful influence of core cooling in reducing CDO2. Despite these large reductions in CDO2 with cold stress, gross indices of cognition remained stable.

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“…Dehydration during exercise is expected, and is directly proportional to exercise intensity, duration, environmental conditions, types of clothes and equipment (24,25,26) . A loss of body mass greater than 2% may negatively affect the cardiovascular system (5,23,30) , immune system (11) , brain function (28,29) , and performance, due to fluid imbalance (24,29) .…”

Section: Introductionmentioning

confidence: 99%

Hydration status of competitive rowers during indoor and outdoor training sessions

Lampert¹,

Alves²,

Varriale³

et al. 2016

RPCD

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Estado de hidratação de remadores de competição durante sessões de treinamento indoor e outdoor RESUMO O remo é caracterizado por altas demandas fisiológicas e desafios ambientais. O objetivo deste estudo foi acessar o nível de hidratação de remadores antes e depois de condições de treinamento indoor e outdoor. Dez remadores homens competitivos (20 ± 4 anos; 11 ± 2% gordura corporal; treinando 4h/ dia, 7 dias/ semana) realizaram duas sessões de treinamento de 16 km, uma indoor (60 min) e uma outdoor (80 min). Foram mensuradas a cor da urina (cartela de cor), a gravidade específica da urina (refratômetro), alterações na massa corporal, ingestão de líquidos e taxa de suor, antes e depois das sessões de treinamento. A desidratação estava presente em pelo menos 70% dos atletas, antes de ambas as sessões de treinamento, como mensurado pela cor da urina e gravidade específica da urina. Houve uma perda de massa corporal maior que 2% em 80% (indoor) e 70% (outdoor) dos remadores. A taxa de suor foi maior no indoor (1.80,7 L.h-1) comparado ao outdoor (1.20,4 L.h-1) (p = .016). A maioria dos remadores iniciou a manhã das sessões de treinamento hipohidratado e desidratou mais ainda, acima de 2% da massa corporal, devido ao suor, durante ambos os treinos. A taxa de suor e as mudanças na massa corporal foram maiores no treinamento indoor.

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Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism

Cited by 51 publications

References 50 publications

Cerebral metabolism, oxidation and inflammation in severe passive hyperthermia with and without respiratory alkalosis

Cerebral metabolism, oxidation and inflammation in severe passive hyperthermia with and without respiratory alkalosis

Global REACH 2018: The influence of acute and chronic hypoxia on cerebral haemodynamics and related functional outcomes during cold and heat stress

Hydration status of competitive rowers during indoor and outdoor training sessions

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