Influence of home-based heat therapy on thermal and cardiovascular strain during passive heat exposure in older adults

Abstract

Heat waves are occurring more frequently and with greater intensity. In fact, 2023 marked the hottest summer ever recorded in the Northern Hemisphere. Heat waves increase the risk for heat-related morbidity and mortality, particularly for older adults who have a reduced ability to dissipate heat. Heat acclimation induces physiological adaptations that attenuate thermal and cardiovascular strain during subsequent heat exposures. However, traditional heat acclimation protocols require expensive equipment (e.g., climate chamber) and may be challenging for older adults with limited functional capacity. Home-based heat therapy provides a potentially safe and pragmatic option to induce heat acclimation. The purpose of this pilot study was to test the hypothesis that home-based heat therapy reduces thermal and cardiovascular strain in older adults during acute passive heat exposure. Six older adults (5 women; 67 ± 4 years) performed 8 weeks of home-based heat therapy by immersing their lower legs ~33 cm into a heated (~ 42°C) and circulated water bath 4 days per week, for 45 min per session. Intestinal temperature (telemetric pill) and heart rate were assessed before (pre) and after (post) the intervention during acute heat exposure (45 min lower leg water immersion). In addition, rate pressure product, an estimate of myocardial demand, was calculated as heart rate x systolic blood pressure. Resting intestinal temperature, heart rate, and rate pressure product did not differ from pre to post heat therapy (all P ≥ 0.6). However, the change in intestinal temperature during acute heat exposure was reduced after heat therapy (15 min: pre, Δ0.47 ± 0.17 °C vs. post, Δ0.33 ± 0.14 °C; 30 min: pre, Δ0.84 ± 0.29 °C vs. post, Δ0.72 ± 0.23 °C; 45 min: pre, Δ1.10 ± 0.27 °C vs. post, Δ1.07 ± 0.24 °C; P = 0.03 for main effect of time). Likewise, the change in heart rate was attenuated following the intervention (15 min: pre, Δ14 ± 9 bpm vs. post, Δ10 ± 5 bpm; 30 min: pre, Δ22 ± 13 bpm vs. post, Δ17 ± 6 bpm; 45 min: pre, Δ25 ± 9 bpm vs. post, Δ21 ± 6 bpm; P = 0.02 for main effect of time). Rate pressure product was also reduced following heat therapy (15 min: pre, Δ1280 ± 1636 bpm·mmHg vs. post, Δ322 ± 698 bpm·mmHg; 30 min: pre, Δ1800 ± 1573 bpm·mmHg vs. post, Δ1170 ± 450 bpm·mmHg; 45 min: pre, Δ2145 ± 593 bpm·mmHg vs. post, Δ840 ± 602 bpm·mmHg; P < 0.01 for main effect of time). Our preliminary data suggest that 8 weeks of home-based heat therapy elicits some adaptations that may reflect heat acclimation. However, further work is needed to confirm these initial findings. American Heart Association TPA958179. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.