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01-12-2020 | Original Article

Hyperthermia and dehydration: their independent and combined influences on physiological function during rest and exercise

Authors: Anne M. J. van den Heuvel, Benjamin J. Haberley, David J. R. Hoyle, Rodney J. Croft, Gregory E. Peoples, Nigel A. S. Taylor

Published in: European Journal of Applied Physiology | Issue 12/2020

Abstract

Purpose

This experiment was designed to quantify the independent and combined influences of hyperthermia and dehydration on effector control during rest and exercise.

Methods

To achieve that, whole-body hydration of healthy adults (N = 8) was manipulated into each of three states (euhydrated, 3% and 5% dehydrated), and then clamped within each of two thermal states (normothermia [mean body temperature: 36.1 °C] and moderate hyperthermia [mean body temperature: 38.2 °C]). Those treatment combinations provided six levels of physiological strain, with resting physiological data collected at each level. The effects of isothermal, thermally unclamped and incremental exercise were then investigated in normothermic individuals during each level of hydration.

Results

At rest, dehydration alone reduced urine flows by 83% (3% dehydrated) and 93% (5% dehydrated), while the reduction accompanying euhydrated hyperthermia was 86%. The sensitivities of renal water conservation to 3% dehydration (−21% mOsm⁻¹ kg H₂O⁻¹) and moderate hyperthermia (−40% °C⁻¹) were independent and powerful. Evidence was found for different renal mechanisms governing water conservation between those treatments. Cutaneous vasomotor and central cardiac responses were unresponsive to dehydration, but highly sensitive to passive thermal stress. Dehydration did not impair either whole-body or regional sweating during rest or exercise, and not even during incremental cycling to volitional exhaustion.

Conclusion

In all instances, the physiological impact of these thermal- and hydration-state stresses was independently expressed, with no evidence of interactive influences. Renal water-conservation was independently and powerfully modified, exposing possible between-treatment differences in sodium reabsorption.

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Title: Hyperthermia and dehydration: their independent and combined influences on physiological function during rest and exercise
Authors: Anne M. J. van den Heuvel
Benjamin J. Haberley
David J. R. Hoyle
Rodney J. Croft
Gregory E. Peoples
Nigel A. S. Taylor
Publication date: 01-12-2020
Publisher: Springer Berlin Heidelberg
Published in: European Journal of Applied Physiology / Issue 12/2020
Print ISSN: 1439-6319
Electronic ISSN: 1439-6327
DOI: https://doi.org/10.1007/s00421-020-04493-4

Keynote webinar | Spotlight on sleep in brain health

Springer Medicine

Hyperthermia and dehydration: their independent and combined influences on physiological function during rest and exercise

Abstract

Purpose

Methods

Results

Conclusion

Keynote webinar | Spotlight on sleep in brain health

Springer Medicine

Abstract

Purpose

Methods

Results

Conclusion

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