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Research Letter |

Cardiac and Thermal Strain of Elderly Adults Exposed to Extreme Heat and Humidity With and Without Electric Fan Use

Daniel Gagnon, PhD1; Steven A. Romero, PhD1; Matthew N. Cramer, PhD1; Ollie Jay, PhD2; Craig G. Crandall, PhD1
[+] Author Affiliations
1Institute for Exercise and Environmental Medicine, University of Texas Southwestern Medical Center, Dallas
2Faculty of Health Sciences, University of Sydney, Lidcombe, Australia
JAMA. 2016;316(9):989-991. doi:10.1001/jama.2016.10550.
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This physiology study investigates whether fan use delays elevations in heart rate and core temperature of older healthy volunteers in response to extreme heat and humidity.

Heat-related morbidity and mortality are important health challenges posed by global climate change.1 Electric fans provide a low-cost and accessible cooling intervention, although their effectiveness remains debatable. Due to theoretical risks of accelerated heat gain and dehydration, fan use is discouraged above ambient temperatures of approximately 35°C.2 However, empirical data to support or refute their use during heat wave conditions are sparse.3

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Figure 1.
Critical Humidity Inflection Points for Heart Rate and Core Temperature

A, The critical humidity at which rapid elevations in heart rate and core temperature occurred was evaluated in elderly adults exposed to stepwise increases in relative humidity while resting at 42°C. The protocol was performed without and with fan use. B, Error bars indicate 95% confidence intervals. The horizontal line indicates the mean. The inflection points for heart rate (P = .68) and core temperature (P = .11) did not differ between conditions.

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Figure 2.
Heart Rate and Core Temperature During the Protocol

Elderly adults were exposed to stepwise increases in relative humidity while resting at 42°C. The protocol was performed without and with fan use (randomized). A significant condition × relative humidity interaction was observed for heart rate and core temperature (both P < .001). Fan use resulted in greater heart rate and core temperature, but the magnitude of difference between conditions generally became less as relative humidity increased. Error bars indicate 95% confidence intervals. Data markers indicate mean values.

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