Age Modulates Physiological Responses during Fan Use under Extreme Heat and Humidity.

Purpose: We examined the effect of electric fan use on cardiovascular and thermoregulatory responses of nine young (26 +/- 3 years) and nine aged (68 +/- 4 years) adults exposed to extreme heat and humidity. Methods: While resting at a temperature of 42[degrees]C, relative humidity increased from 30 to 70% in 2% increments every 5 minutes. On randomized days, the protocol was repeated without or with fan use. Heart rate (HR), core (Tcore) and mean skin (Tsk) temperatures were measured continuously. Whole-body sweat loss (WBSL) was measured from changes in nude body weight. Other measures of cardiovascular (cardiac output), thermoregulatory (local cutaneous and forearm vascular conductance, local sweat rate), and perceptual (thermal and thirst sensations) responses were also examined. Results: When averaged over the entire protocol, fan use resulted in a small reduction of HR (-2 beats/min, 95% CI: -8 to 3), and slightly greater Tcore (+0.05[degrees]C, 95% CI: -0.13 to 0.23) and Tsk (+0.03[degrees]C, 95% CI: -0.36 to 0.42) in young adults. In contrast, fan use resulted in greater HR (+5 beats/min, 95% CI: 0 to 10), Tcore (+0.20[degrees]C, 95% CI: 0.00 to 0.41) and Tsk (+0.47[degrees]C, 95% CI: 0.18 to 0.76) in aged adults. A greater WBSL during fan use was observed in young (+0.2 kg, 95% CI: -0.2 to 0.6) but not aged (0.0 kg, 95% CI: -0.2 to 0.2) adults. Greater local sweat rate and cutaneous vascular conductance were observed with fan use in aged adults. Other measures of cardiovascular, thermoregulatory and perceptual responses were unaffected by fan use in both groups. Conclusion: During extreme heat and humidity, fan use elevates physiological strain in aged, but not young, adults. (C) 2017 American College of Sports Medicine

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