Protective Cooling Measures to Safeguard Elderly People From Dangerous Summer Heat

Evaluating the Efficacy of Cooling Centres for Limiting Heat Strain in Elderly Adults During Extreme Heat Events

With the increasing incidence and severity of extreme heat events accompanying climate change, there is an urgent need for sustainable cooling strategies to protect heat-vulnerable older adults, who are at increased risk of adverse health events during heat stress. Health agencies including the World Health Organization, the United States Centers for Disease Control and Prevention, and Health Canada currently recommend visiting a cooling centre or other air-conditioned location for 1-3 hours per day during extreme heat events to mitigate hyperthermia and strain on the cardiovascular system and therefore the risk adverse health events. However, our recent trial shows that while brief air-conditioning exposure is effective for reducing body temperature and cardiovascular burden in healthy older adults, the physiological impacts of cooling abate quickly following return to the heat. The purpose of this project is therefore to assess whether shorter but more frequent air-conditioning exposure provides more effective cooling than current recommendations (a single 1-3-hour cooling bout) in older adults with or without common chronic health conditions associated with increased vulnerability to extreme heat. This will be accomplished by evaluating physiological strain in older adults with and without diabetes and/or hypertension exposed for 8 hours to conditions reflective of extreme heat events in temperate, continental climates (35°C, 60% relative humidity). Participants will complete 3 separate simulated heat event exposures: i) a control trial (no cooling throughout the 8-hour heat event); ii) a recommended cooling trial (3 hours of heat exposure followed by 2 hours cooling); and iii) a hybrid cooling trial (2 hours of heat exposure followed by 1 hour cooling, another 2 hours heat exposure followed by 1 hour cooling, and a final 2-hour heat exposure).

Heat wave, Cooling center, Heat strain, Cardiovascular strain, Heat and health protection, Extreme heat events, Thermal comfort

Participant will complete 3 simulated extreme heat event exposures in random order: i) no cooling center intervention (control); ii) recommended cooling center intervention (1 x 2-hours of brief air-conditioning); and iii) hybrid cooling center intervention (2 x 1-hour interspersed brief air-conditioning)

Participants will be informed of the study interventions before providing informed consent but will be blinded to the specific trial condition at each of the 3 laboratory visits (control, recommended cooling, hybrid cooling). Data will be blinded prior to analysis.

Participants are exposed to 35°C, 60% relative humidity for 3 hours, are then moved to an air-conditioned room for 2 hours (~23°C, ~50% relative humidity), and then return to the heat for a final 3 hours.

Participants are exposed to 35°C, 60% relative humidity for 2 hours, are moved to an air-conditioned room for 1 hour (~23°C, ~50% relative humidity), return to the heat for 2 hours, move back to the air-conditioned room for 1 hour, and then return to the heat for a final 2 hours

Rectal temperature will be measured continuously throughout each exposure and the area under the curve will be calculated.

Heart rate will be measured continuously throughout each exposure and the area under the curve will be calculated.

Body fluid loss calculated as a change in body weight from pre-exposure values (corrected for food intake and deification).

30:15 ratio calculated as the ratio of the RR interval measured after 30 heart beats following standing from a supine position to that measured after 15 heart beats.

Inclusion Criteria: Adult aged 60-85 years Male or female Body mass index < 35 kg/m2 For participants with type 2 diabetes: at least one year lapsed since diagnosis and hemoglobin A1c 6.0-10.5%. For participants with hypertension: at least one year lapsed since diagnosis or average resting blood pressure >140 systolic or >90 diastolic Exclusion Criteria: Currently smoking or quit <5 years ago Moderate or serious medical conditions (other than Type 2 diabetes or high blood pressure), particularly those known to influence physiological responses to heat exposure (e.g., diagnosed heart disease, neurological disorders) Heat adapted due to repeated exposure to hot environments (use sauna, recent travel to hot climates, other) For participants with type 2 diabetes: "Brittle" diabetes: unpredictable hypo- & hyperglycemia. Severe cardiovascular autonomic or peripheral neuropathy (guidelines.diabetes.ca/cpg)

Deidentified participant data will be available from Dr. Kenny upon reasonable request and signed access agreement.