Use of a Water‐soaked Garment, with and without an Electric Fan, to Mitigate Thermal Strain in Older Individuals under Heat Wave Conditions

Abstract

As average global surface temperatures are projected to rise, and heat waves are expected to increase in frequency, duration, and intensity, exposure to high levels of heat stress will occur with greater regularity. Older individuals are particularly vulnerable to heat stress, evidenced by excess hospitalizations and mortality among individuals aged >60 years. With the continue rise of electricity costs coupled with vulnerable regions that do not have easy access to air conditioning, it is imperative to find alternative cooling strategies that are cost‐effective and accessible for older individuals. The present study evaluated whether wearing a water‐soaked t‐shirt, with and without electric fan use, mitigates thermal and cardiovascular strain under heat wave conditions. Nine healthy older individuals (68 ± 4 years; five females) completed three, 120‐min heat exposures (42.4 ± 0.2°C, 34.2 ± 0.9% relative humidity) on separate occasions while wearing either a dry t‐shirt (CON), a t‐shirt soaked with 500 ml of tap water (WET), or a t‐shirt soaked with 500 ml of tap water while facing an electric fan forcing air at 2.4 ± 0.4 m/s (WET+FAN). Measurements included core and mean skin temperatures, evaporative mass loss, heart rate, and blood pressure. The rise in core temperature was attenuated by ~0.3°C in WET compared to DRY and WET+FAN during the first hour of heat stress (P < 0.01). At 120 min, the rise in core temperature remained attenuated by ~0.2 °C in WET compared to DRY (P=0.0016), while other comparisons were not different. After the 120‐min heat exposure, changes in body mass, which largely reflect evaporation of sweat and moisture trapped in clothing, were greatest in WET+FAN, followed by WET, and then DRY (P < 0.01). However, sweat losses were lowest in WET, followed by DRY, and then WET+FAN (P < 0.01). Heart rate was lower during the first hour in WET vs. DRY, and at 30 min only in WET vs. WET+FAN (P < 0.01). No differences in mean arterial pressure were found (P = 0.51). In conclusion, simply wearing a water‐soaked t‐shirt is an effective heat management strategy to mitigate thermal and cardiovascular strain and lower sweat losses in older people exposed to heat wave conditions. Conversely, the cooling benefits of a water‐soaked t‐shirt are eliminated when used in combination with a fan.Support or Funding InformationFunding: National Institutes of Health (R01GM068865) and Department of Defense – US Army (W81XWH‐15‐1‐0647)