Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion
Lucas RAI, Wilson LC, Ainslie PN, Fan JL, Thomas KN, Cotter JD
American journal of physiology. Regulatory, integrative and comparative physiology · 10 citations
Review labels
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How it was studied
- Design
- Controlled clinical trial (classified by our AI screen)
- Studied in
- People
- Main outcome
- Health markers and function
Who paid for it
- Funding
- Funding not disclosed
Publication
- Published
- 2017-12-06 · Am J Physiol Regul Integr Comp Physiol · vol. 314 · issue 3 · pp. R415–R426
- Publisher
- American Physiological Society
- Cited
- 15 citations · more than 71% of similar papers · 0.7× the field average
- References
- 51 works
- Access
- Paywalled
- Research areas
- Thermoregulation and physiological responses · Climate Change and Health Impacts · Thermal Regulation in Medicine
- Keywords
- Medicine, Supine position, Mean arterial pressure, Blood pressure, Hypocapnia, Heart rate, Cardiology, Perfusion, Internal medicine, Orthostatic vital signs, Anesthesia, Cardiorespiratory fitness
- MeSH
- middle cerebral artery, humans, hypotension, orthostatic, dehydration, heat stress disorders, hypocapnia, blood flow velocity, cardiac output, lower body negative pressure, severity of illness index, body temperature regulation, heart rate, cerebrovascular circulation, adult, male, young adult, arterial pressure, organism hydration status
6 authors
From GB, NZ, CA, CH
- Rebekah A. I. LucasUniversity of Birmingham; University of Otago
- Luke C. Wilson · correspondingUniversity of Otago
- Philip Neil AinslieUniversity of British Columbia; University of British Columbia, Okanagan Campus; University of Otago
- Jui‐Lin FanUniversity of Otago; University of Lausanne
- Kate Nicole ThomasUniversity of Otago
- James David CotterUniversity of Otago
Abstract
The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (Tc; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5-2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAvmean; transcranial Doppler), partial pressure of end-tidal carbon dioxide ([Formula: see text]), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, -15, -30, and -45 mmHg). Four subjects became intolerant before +2.0°C Tc, unrelated to hydration status. Without LBNP, decreases in [Formula: see text] accounted fully for reductions in MCAvmean across all Tc. With LBNP at heat tolerance (+1.5 or +2.0°C), [Formula: see text] accounted for 69 ± 25% of the change in MCAvmean. The HYPO condition did not affect MCAvmean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAvmean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in Tc are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.
Abstract via Europe PMC. Copyright remains with the authors or publisher.
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