Author(s): PICCOLO, D., CORBETT, J., JAMES, T., COSTELLO, J., WILLIAMS, T., EXELL, T., MOORE, J., WRIGHT, A., MAYES, H., ALNAJJAR, M., HUDSON, L., MARSH, P., PRASKACOVA, V., PERISSIOU, M., SAYNOR, Z., SHEPHERD, A., Institution: UNIVERSITY OF PORTSMOUTH, Country: UNITED KINGDOM, Abstract-ID: 1401

INTRODUCTION:
Hot water immersion (HWI) has emerged as a potential method to improve health outcomes, but research in older people is limited. This multi-experiment study aimed to assess the effects of acute and repeated HWI on cardiovascular, cognitive and muscle function, heat shock proteins (HSPs) and inflammatory biomarkers.
METHODS:
To assess acute HWI, 16 healthy older adults (aged 67 ± 10 years, body mass index (BMI) 25.3 ± 3.7 kg.m2 completed a 60-minute HWI in 40°C water (acute HWI; target rectal temperature 38.5-39.0°C), Thereafter, the time course of macrovascular function (brachial flow-mediated dilation [FMD] and common carotid artery blood flow [CCA-BF]), microvascular endothelial function (via transdermal delivery of acetylcholine and insulin), central haemodynamics (heart rate [HR]; stroke volume and cardiac indexes), cognitive performance (working memory, reaction time, logical reasoning), measures of cerebral oxygenation, plasma HSPs ([eHSP27], [eHSP60], [eHSP70], [eHSP90]), and inflammation [interleukin (IL) -6], [IL-10] and [Tumor necrosis factor-α (TNF-α)]) were assessed across the subsequent 48 hours. To assess repeated HWI, 12 healthy older adults (aged 69 ± 10 years, BMI 25.2 ± 4.1 kg.m2), who also completed acute HWI testing, were randomised to a six-week HWI intervention (2-3 x 60-minute HWIs/week; target rectal temperature 38.5-39.0°C) or control condition with a six-week washout prior to crossover. Pre- and post-intervention measurements were collected for each arm. Assessments included macro- and microvascular function, cognitive performance with cerebral oxygenation during the first and final HWI sessions, muscle strength (isokinetic and handgrip dynamometry), lower body power and functional performance (Short Physical Performance Battery [SPPB] with motion and external force capture), and plasma [eHSP27], [eHSP60], [eHSP70], [eHSP90], [IL-6], [IL-10] and [TNF-α].
RESULTS:
Acute HWI improved reaction time and 2-back performance, increased FMD time to peak dilation, and reduced insulin AUC during transdermal delivery and cerebral oxygenation (P < 0.05), of which all but reaction time returned to baseline by 48 hours post-HWI. Acute HWI did not alter FMD%, CCA-BF, central haemodynamics, logical reasoning, or plasma [eHSPs] and [inflammatory biomarkers]. Repeated HWI reduced resting HR, improved working memory and logical reasoning, and increased knee power (all P < 0.05). Repeated HWI had no effect on FMD, CCA-BF, microvascular endothelial function, central haemodynamics, reaction time, 2-back, muscle strength, SPPB performance or plasma [eHSPs] and [inflammatory biomarkers] (all P > 0.05).
CONCLUSION:
Acute HWI transiently reduced macro- and microvascular function and improved cognitive performance but did not alter plasma [eHSPs] or inflammation. Repeated HWI improved cognitive performance and HR, but had no effect on macro- and microvascular function, central haemodynamics, muscle strength, SPPB performance, eHSPs or inflammation in healthy older adults.