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, ) or without (control group, ) a cooling intervention consisting of 2-h rest in an air-conditioned room ( , 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 ( ; hour 6), and it remained 0.3°C (95% CI: 0.2, 0.4) lower an hour after returning to the heat ( ; hour 7). Despite this, core temperatures in each group were statistically equivalent at hours 8 and 9, within ( ). Cooling also acutely reduced demand on the heart and improved indices of cardiovascular autonomic function ( ); however, these outcomes were not different between groups at the end of exposure ( ). 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

Invited Perspective: Cooling Centers and Heat Waves—Can Current Data Inform Guidance?

“…Based on the lower core temperature measured in the cooling group during hours 4–6, Meade et al. 16 state, “our data lend mechanistic support for epidemiological reports indicating up to a 66% reduction in the odds of heat-related mortality in older adults who visited cooled locations during heat waves.” This statement is noteworthy. Although their data show an expected reduction in core temperature and heart rate following removal from the heat, in the author’s opinion, no data are presented that provide insight regarding the pathophysiological mechanisms involved in heat-related mortality or how such mechanisms are affected by brief cooling periods.…”

“…Despite these limitations, the study by Meade et al. 16 is of undeniable importance, especially in the context of climate change. Prior to this study, the physiological responses of older individuals to visiting a cooling center (although simulated) were unknown.…”

“…In this issue of Environmental Health Perspectives , Meade et al. 16 publish findings from a comprehensive study investigating primarily the thermal (rectal/core body temperature) response to a simulated 9-h heat wave in older adult volunteers (age range, 64–79 y). Using an environmental chamber set at 40°C air temperature and 9% relative humidity (heat index of 37°C), 20 control (no-cooling) participants rested in the heat for 9 h, whereas 20 (the “cooling group”) were provided a 2-h cooling break in 23°C air temperature between hours 4 and 6.…”

“…Interventions such as water dousing, limb immersion, electric fans, or the application of wetted clothing are important strategies to help mitigate thermal strain in the absence of AC. 19 Although AC produced a more robust cooling effect than other methods, 16 major benefits of alternative “home-based” methods are that they are cheap, simple to implement, sustainable, and usable for bedbound patients. It is important to note, however, that the efficacy of electric fans for removing body heat depends on the air temperature and humidity combination.…”

“…Thus, they note, traveling to a cooling center may offset some of the proposed benefits—an important consideration that was not simulated in Meade et al.’s experimental protocol. 16 …”