Evaluating low-energy cooling strategies on thermal and cardiac strain in older adults exposed to very hot and dry heat with accompanying activities of daily living.

Abstract

We tested the hypothesis that skin wetting would attenuate, whereas electric fans would increase, thermal and cardiac strain in older adults exposed to very hot and dry heat. Twenty-three older adults (66-84 yr) were exposed (randomized) to 3 h of ambient heating (47°C and 15% relative humidity) with water spray, fan use, water spray + fan use, or no cooling intervention. We assessed thermal, cardiovascular, and cardiac responses. Compared with control, water spray reduced the increase in core temperature by -0.24°C [95% CI: -0.42, -0.06] (P = 0.007), ending skin temperature by -2.1°C [-2.6, -1.5] (P < 0.001), sweat rate by -0.12 L/h [-0.15, -0.09] (P < 0.001), ending heart rate by -5 beats/min [-8, -1] (P = 0.004), and ending rate pressure product by -1,027 beats/min·mmHg [-1,733, -321] (P = 0.004). Fan use augmented the increase in core temperature by 0.60°C [0.36, 0.84] (P < 0.001), ending skin temperature by 1.5°C [0.9, 2.1] (P < 0.001), sweat rate by 0.17 L/h [0.13, 0.20] (P < 0.001), ending heart rate by 15 beats/min [8, 23] (P < 0.001), and ending rate pressure product by 2,326 beats/min·mmHg [780, 3,872] (P = 0.003). Water spray + fan had no effect on core temperature (P = 0.308) or skin temperature (P = 0.114). However, sweat rate (0.07 L/h [0.001, 0.13]; P = 0.031) and ending heart rate (8 beats/min [1, 15]; P = 0.046) were higher with water spray + fan. Water spray attenuates, whereas fans increase, thermal and cardiac strain in older adults exposed to very hot and dry conditions. Thus, electric fans are not advised as a cooling intervention under the assessed conditions. Water spray offers some cooling benefits when access to energy is unavailable.NEW & NOTEWORTHY Extreme heat increases morbidity and mortality, particularly among older adults. Air conditioning can mitigate heat strain but may be inaccessible; thus, there is a need to identify nonair conditioning-dependent cooling strategies. We show that water spray attenuates, whereas fans increase, thermal and cardiac strain in older adults exposed to very hot and dry conditions. Importantly, our findings highlight that water spray offers the greatest benefit for individuals who are vulnerable to hyperthermia and tachycardia associated with heat stress.