Efficacy of Cooling Centers for Mitigating Physiological Strain in Older Adults during Daylong Heat Exposure: A Laboratory-Based Heat Wave Simulation

Abstract

Background: Health agencies, including the U.S. Centers for Disease Control and Prevention and the World Health Organization, recommend that heat-vulnerable older adults without home air-conditioning should visit cooling centers or other air-conditioned locations (e.g., a shopping mall) during heat waves. However, experimental evidence supporting the effectiveness of brief air-conditioning is lacking.

Objective: We evaluated whether brief exposure to an air-conditioned environment, as experienced in a cooling center, was effective for limiting physiological strain in older adults during a daylong laboratory-based heat wave simulation.

Methods: Forty adults 64-79 years of age underwent a 9-h simulated heat wave (heat index: 37°C) with (cooling group, $n=20$) or without (control group, $n=20$) a cooling intervention consisting of 2-h rest in an air-conditioned room ($\sim 23°C$, hours 5-6). Core and skin temperatures, whole-body heat exchange and storage, cardiovascular function, and circulating markers of acute inflammation were assessed.

Results: Core temperature was 0.8°C (95% CI: 0.6, 0.9) lower in the cooling group compared with the control group at the end of the cooling intervention ($p<0.001$; hour 6), and it remained 0.3°C (95% CI: 0.2, 0.4) lower an hour after returning to the heat ($p<0.001$; hour 7). Despite this, core temperatures in each group were statistically equivalent at hours 8 and 9, within $\pm 0.3°C$ ($p\le 0.005$). Cooling also acutely reduced demand on the heart and improved indices of cardiovascular autonomic function ($p\le 0.021$); however, these outcomes were not different between groups at the end of exposure ($p\ge 0.58$).

Discussion: Brief air-conditioning exposure during a simulated heat wave caused a robust but transient reduction in core temperature and cardiovascular strain. These findings provide important experimental support for national and international guidance that cooling centers are effective for limiting physiological strain during heat waves. However, they also show that the physiological impacts of brief cooling are temporary, a factor that has not been considered in guidance issued by health agencies. https://doi.org/10.1289/EHP11651.