Heat waves and the elderly: reducing thermal and cardiovascular consequences

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Abstract Heat waves are lethal and cause a disproportionate number of deaths in the elderly relative to any other age group. It is important to note that such deaths are primarily cardiovascular, not hyperthermia itself, in origin. Nevertheless, we know relatively little about the effects of aging on cardiovascular function during actual heat wave-like conditions. The central hypothesis of this work is that the elderly exhibit impaired cardiovascular responses during heat wave conditions, which can be mitigated by employing low- energy demand cooling strategies. Aim 1 will test will test the hypothesis that aging impairs otherwise necessary cardiovascular responses during prolonged exposure to heat wave conditions. Comprehensive cardiovascular and thermal responses in the elderly, relative to younger adults, will be evaluated during exposure to two prolonged heat wave conditions: hot and humid (replicating the 1995 Chicago heat wave), very hot and dry (replicating the 2018 Los Angeles heat wave). Aim 2A will test the hypothesis that skin wetting is an effective modality to attenuate elevations in core body temperature and accompanying cardiovascular strain in the elderly during heat waves. Though air conditioning is the most effective strategy to prevent heat-related morbidity and mortality, ~12% of Americans do not have access to air conditioners, and this percentage is likely higher in the Midwest and Northeast United States where injury and deaths during heat waves are particularly high. Moreover, variables such as socio-economic factors, power outages, and government-imposed rolling blackouts threaten region-wide access to air conditioning at times when it is most needed. This aim will assess the efficacy of skin wetting only, fan use only, and a combination of skin wetting and fan use in mitigating excessive elevations in core body temperature and associated cardiovascular strain in the elderly during both types of heat waves outlined in Aim 1. Aim 2B will test the hypothesis that thermoregulatory and cardiovascular strain during heat waves will be mitigated in the elderly after a 10 day home-based heat acclimation regimen. Heat acclimation is the process by which repeated exposure to heated conditions improves the capacity to tolerate, and even survive, a subsequent heat stress. This aim will evaluate the efficacy of an easily implemented, inexpensive, and novel home-based heat acclimation regimen (i.e., 10 continuous days of lower-leg hot water immersion for 90 min/day) in attenuating excessive elevations in core body temperature and associated cardiovascular strain in elderly adults during the same heat wave conditions outlined in Aim 1. The expected outcomes from this body of work will re-shape our understanding of the consequences of aging on cardiovascular function during heat waves, as well as identify the potential of low-energy cooling modalities directed towards saving the lives of this vulnerable population during heat wave exposure.