Improvements in Orthostatic Tolerance with Exercise Are Augmented by Heat Acclimation: A Randomized Controlled Trial.

Autor:	Parsons IT, Snape D; Carnegie School of Sport, Leeds Beckett University, Leeds, UNITED KINGDOM., Stacey MJ; Research and Clinical Innovation, Royal Centre for Defence Medicine, Birmingham, UNITED KINGDOM., Barlow M; Carnegie School of Sport, Leeds Beckett University, Leeds, UNITED KINGDOM., O'Hara J; Carnegie School of Sport, Leeds Beckett University, Leeds, UNITED KINGDOM., Gall N; School of Cardiovascular Medicine and Sciences, King's College London, London, UNITED KINGDOM., Chowienczyk P; School of Cardiovascular Medicine and Sciences, King's College London, London, UNITED KINGDOM., Wainwright B; Carnegie School of Sport, Leeds Beckett University, Leeds, UNITED KINGDOM., Woods DR
Jazyk:	angličtina
Zdroj:	Medicine and science in sports and exercise [Med Sci Sports Exerc] 2024 Apr 01; Vol. 56 (4), pp. 644-654. Date of Electronic Publication: 2023 Nov 27.
DOI:	10.1249/MSS.0000000000003355
Abstrakt:	Introduction: Heat adaptation is protective against heat illness; however, its role in heat syncope, due to reflex mechanisms, has not been conclusively established. The aim of this study was to evaluate if heat acclimation (HA) was protective against heat syncope and to ascertain underlying physiological mechanisms. Methods: Twenty (15 males, 5 females) endurance-trained athletes were randomized to either 8 d of mixed active and passive HA (HEAT) or climatically temperate exercise (CONTROL). Before, and after, the interventions participants underwent a head up tilt (HUT) with graded lower body negative pressure (LBNP), in a thermal chamber (32.0 ± 0.3°C), continued until presyncope with measurement of cardiovascular parameters. Heat stress tests (HST) were performed to determine physiological and perceptual measures of HA. Results: There was a significant increase in orthostatic tolerance (OT), as measured by HUT/LBNP, in the HEAT group (preintervention; 28 ± 9 min, postintervention; 40 ± 7 min) compared with CONTROL (preintervention; 30 ± 8 mins, postintervention; 33 ± 5 min) ( P = 0.01). Heat acclimation resulted in a significantly reduced peak and mean rectal and skin temperature ( P < 0.01), peak heat rate ( P < 0.003), thermal comfort ( P < 0.04), and rating of perceived exertion ( P < 0.02) during HST. There was a significantly increased plasma volume (PV) in the HEAT group in comparison to CONTROL ( P = 0.03). Conclusions: Heat acclimation causes improvements in OT and is likely to be beneficial in patients with heat exacerbated reflex syncope. Heat acclimation-mediated PV expansion is a potential physiological mechanism underlying improved OT. (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)
Databáze:	MEDLINE
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