The effect of age and mitigation strategies during hot water immersion on orthostatic intolerance and thermal stress.

Abstract

What is the central question of this study? The aim was to characterize adverse responses to whole-body hot water immersion and to investigate practical strategies to mitigate these effects. What is the main finding and its importance? Whole-body hot water immersion induced transient orthostatic hypotension and impaired postural control, which recovered to baseline within 10min. Hot water immersion was well tolerated by middle-aged adults, but younger adults suffered from a greater frequency and severity of dizziness. Cooling the face with a fan or not immersing the arms can mitigate some of these adverse responses in younger adults. Hot water immersion improves cardiovascular health and sporting performance, yet its adverse responses are understudied. Thirteen young and 17 middle-aged adults (n=30) were exposed to 2×30min bouts of whole-body 39°C water immersion. Young adults also completed cooling mitigation strategies in a randomized cross-over design. Orthostatic intolerance and selected physiological, perceptual, postural and cognitive responses were assessed. Orthostatic hypotension occurred in 94% of middle-aged adults and 77% of young adults. Young adults exhibited greater dizziness upon standing (young subjects, 3 out of 10 arbitrary units (AU) vs. middle-aged subjects, 2 out of 10 AU), with four terminating the protocol early owing to dizziness or discomfort. Despite middle-aged adults being largely asymptomatic, both age groups had transient impairments in postural sway after immersion (P<0.05), but no change in cognitive function (P=0.58). Middle-aged adults reported lower thermal sensation, higher thermal comfort, and higher basic affect than young adults (all P<0.01). Cooling mitigation trials had 100% completion rates, with improvements in sit-to-stand dizziness (P<0.01, arms in, 3 out of 10 AU vs. arms out, 2 out of 10 AU vs. fan, 4 out 10 AU), lower thermal sensation (P=0.04), higher thermal comfort (P<0.01) and higher basic affect (P=0.02). Middle-aged adults were predominantly asymptomatic, and cooling strategies prevented severe dizziness and thermal intolerance in younger adults.