With the increasing regularity and intensity of hot weather and heat waves, there is an urgent need to develop heat-alleviation strategies able to provide targeted protection for heat-vulnerable older adults. While air-conditioning provides the most effective protection from extreme heat, it is inaccessible for many individuals. Air-conditioning is also energy intensive, which can strain the electrical grid and, depending on the source of electricity generation, contribute to increasing green house gas emissions. For these reasons, recent guidance has advocated the use of electric fans as a simple and sustainable alternative to air-conditioning. To date, however, only one study has assessed the efficacy of fan use in older adults and demonstrated that fans accelerate increases in body temperature and heart rate in a short-duration (\~2 hours) resting exposure to 42°C with increasing ambient humidity from 30-70%. While subsequent modelling has suggested that fans can improve heat loss via sweat evaporation in healthy older adults at air temperatures up to 38°C, there is currently no empirical data to support these claims. Further, that work assumed older adults were seated in front of a pedestal fan generating an airflow of 3·5-4·5 m/s at the front of the body. This airflow cannot be attained by most marketed pedestal fans. Studies are therefore needed to evaluate the efficacy of fans for preventing hyperthermia and the associated physiological burden in older adults in air temperatures below 38°C and determine whether the cooling effect of fans, if any, is evident at lower rates of airflow. To address these knowledge gaps, this randomized crossover trial will evaluate body core temperature, cardiovascular strain, dehydration, and thermal comfort in adults aged 65-85 years exposed for 8 hours to conditions experienced during hot weather and heat waves in North America simulated using a climate chamber (36°C, 45% relative humidity). Each participant will complete three randomized exposures that will differ only in the airflow generated at the front of the body via an electric pedestal fan: no airflow (control), low airflow (\~2 m/s), and high airflow (\~4 m/s). While participants will spend most of the 8-hour exposure seated in front of the fan, they will also complete 4 x 10 min periods of 'activities of daily living' (\~2-2.5 METS, light stepping) at \~2 hour intervals to more accurately reflect activity patterns in the home.
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Core temperature (peak)
Timeframe: End of heat exposure (hour 8)