Intermittent Hand and Forearm Cool Water Immersion Reduces Thermal and Cardiovascular Strain in Older Adults during Uncompensable Heat Stress (PSU HEAT Project)

As a result of the increasing duration, frequency, and severity of heat waves, adults over the age of 65 will experience deleterious health effects at a significantly greater rate than any other age cohort. Importantly, older adults who succumb to heat-related illnesses are often in an indoor environment with little to no access to air conditioning. Therefore, it is important to identify feasible, sustainable, and effective cooling interventions for older adults during extreme heat stress. The purpose of this study was to identify the effectiveness of intermittent hand and forearm water immersion on reducing thermal and cardiovascular strain in older adults at rest during uncompensable, humid heat stress. We hypothesized that intermittent hand and forearm water immersion would attenuate the rise in core temperature (T c ) and heart rate (HR) compared to trials with no cooling.Twelve older adults (6 F; 65-89 yrs) were exposed to 2 hours of extreme heat stress at 34°C and 77% relative humidity during seated rest. Participants completed intervention trials (hand and forearm water immersion) and no intervention trials. During intervention trials, participants immersed both hands and forearms in cool tap water (~20°C) for 10 min at min 60 and 90 of the experiment. T c , skin temperature (T sk ), and HR were continuously monitored, and blood pressure and rate pressure product (RPP) were recorded every 10 min. Data were analyzed as absolute changes, as well as a delta from min 50 (i.e., immediately before cooling).Absolute, and delta, T c , T sk , and HR increased over time (all p ≤ 0.01); however, intermittent hand and forearm water immersion attenuated and/or prevented this increase (all p ≤ 0.046). Further, absolute and delta RPP increased over time (all p = 0.02), but absolute RPP was attenuated with hand and forearm water immersion (p = 0.003). Mean arterial pressure did not change over time (all p ≥ 0.07) nor with the intervention (all p ≥ 0.2). These data suggest thatacute, intermittenthand and forearm water immersion effectively attenuates thermal and cardiovascular strain for older adults at rest in uncompensable heat stress. These results are the first to show that hand and forearm water immersion is an effective cooling strategy for older adults and provide concrete data for the implementation of evidence-based safety interventions to reduce heat-related morbidity and mortality for older adults. Supported by NIH Grant R01 AG067471 (to W.L.K.) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.