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).
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
DOUBLE
Enrollment
60
Participants are exposed to 35°C, 60% relative humidity for 8 hours.
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
University of Ottawa
Ottawa, Ontario, Canada
Core temperature (peak)
Peak rectal temperature measured during the 8-hour heat exposure.
Time frame: 8-hour heat exposure
Core temperature (AUC)
Rectal temperature will be measured continuously throughout each exposure and the area under the curve will be calculated.
Time frame: 8-hour heat exposure
Heart rate temperature (peak)
Peak rectal temperature measured during the 8-hour heat exposure.
Time frame: 8-hour heat exposure
Heart rate (AUC)
Heart rate will be measured continuously throughout each exposure and the area under the curve will be calculated.
Time frame: 8-hour heat exposure
Mean skin temperature
Mean skin temperature calculated as a weighted average of skin temperatures at 8 body regions.
Time frame: Before and continuously throughout each 8 hour exposure
Arterial blood pressures
Systolic and diastolic pressures measured in triplicate.
Time frame: Every hour during the 8-hour heat exposure
SDNN
Standard deviation of normal-to-normal R-R intervals measured via 3-lead ECG.
Time frame: Every hour during the 8-hour heat exposure
RMSSD
Root mean squared standard deviation of normal-to-normal R-R intervals measured via 3-lead ECG.
Time frame: Every hour during the 8-hour heat exposure
Rate pressure product
Rate pressure product calculated as systolic blood pressure x heart rate.
Time frame: Every hour during the 8-hour heat exposure
Body fluid loss
Body fluid loss calculated as a change in body weight from pre-exposure values (corrected for food intake and deification).
Time frame: Every hour during the 8-hour heat exposure
Stand test: 30:15 ratio
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.
Time frame: Prior to and following the 8-hour heat exposure
Stand test: Systolic response to standing
Fall in systolic blood pressure after standing from a supine position.
Time frame: Prior to and following the 8-hour heat exposure
Baroreflex sensitivity
Baroreflex sensitivity determined during cyclic stand-squat manoeuvres.
Time frame: Prior to and following the 8-hour heat exposure
Change in plasma volume
Change in plasma volume calculated from venous blood samples (Dill and Costill technique)
Time frame: Prior to and following the 8-hour heat exposure
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