Effects of mild hypohydration on cooling during cold-water immersion following exertional hyperthermia

• Published in: European journal of applied physiology Vol. 116; no. 4; pp. 687 - 695
• Main Authors: Butts, Cory L., Luhring, Katherine E., Smith, Cody R., Tucker, Matthew A., Moyen, Nicole E., Ganio, Matthew S., McDermott, Brendon P.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-04-2016; Springer Nature B.V
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Blood; Body fat; Body Temperature - physiology; Cold; Cold Temperature; Cooling; Exercise; Female; Fever; Heart rate; Heat; Human Physiology; Humans; Hydration; Hyperthermia; Hyperthermia, Induced; Hypothermia, Induced; Ice; Immersion; Male; Occupational Medicine/Industrial Medicine; Original Article; Skin; Sports Medicine; Temperature; Water-Electrolyte Balance - physiology; Hypohydration; Dehydration; Exertional heat illness treatment; Cold-water immersion; Exertional hyperthermia
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-016-3329-7

Purpose
We investigated the effects of mild hypohydration compared to euhydration on the cooling efficacy of cold-water immersion (CWI).
Methods
Fourteen participants (eight male, six female; age 26 ± 5 years; ht 1.77 ± 0.08 m; wt 72.2 ± 8.8 kg; 20.6 ± 7.4 % body fat) completed one euhydrated (EU) trial followed by one hypohydrated trial (HY; via 24 h fluid restriction) in an environmental chamber (33.6 ± 0.9 °C, 55.8 ± 1.7 % RH). Volitional exercise was performed in a manner that matched end-exercise rectal temperature (
T
re
) through repeating exercise mode and intensity. Participants were then immersed in ice water (2.0 ± 0.8 °C) until
T
re
reached 38.1 °C or for a maximum of 15 min.
T
re
, heart rate (HR), skin blood flux (SBF) and mean skin temperature (
T
sk
) were monitored continuously during cooling.
Results
Pre-cooling body mass was decreased in the HY trial (−2.66 ± 1.23 % body mass) and maintained in the EU trial (−0.66 ± 0.44 %) compared to baseline mass (
P
 < 0.001). Cooling rates were faster when EU (0.14 ± 0.05 °C/min) compared to HY (0.11 ± 0.05 °C/min,
P
 = 0.046). HR, SBF, and
T
sk
were not different between EU and HY trials (
P
 > 0.05), however, all variables significantly decreased with immersion independent of hydration status (
P
 < 0.001).
Conclusion
The primary finding was that hypohydration modestly attenuates the rate of cooling in exertionally hyperthermic individuals. Regardless of hydration status, the cooling efficacy of CWI was preserved and should continue to be utilized in the treatment of exertional hyperthermia.