Aging, Heat Stress, Heat; Weather, Hypertension, Hyperthermia, Type2 Diabetes
Conditions
Keywords
Heat wave, Cooling center, Heat strain, Cardiovascular strain, Heat and health protection, Extreme heat events, Thermal comfort
Brief summary
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).
Interventions
OTHERNo cooling (control)
Participants are exposed to 35°C, 60% relative humidity for 8 hours.
OTHERRecommended cooling
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.
OTHERHybrid cooling
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
Sponsors
University of Ottawa
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
DOUBLE (Subject, Outcomes Assessor)
Masking description
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.
Intervention model description
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)
Eligibility
Sex/Gender
ALL
Age
60 Years to 85 Years
Healthy volunteers
Yes
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)
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Core temperature (peak) | 8-hour heat exposure | Peak rectal temperature measured during the 8-hour heat exposure. |
| Core temperature (AUC) | 8-hour heat exposure | Rectal temperature will be measured continuously throughout each exposure and the area under the curve will be calculated. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Mean skin temperature | Before and continuously throughout each 8 hour exposure | Mean skin temperature calculated as a weighted average of skin temperatures at 8 body regions. |
| Arterial blood pressures | Every hour during the 8-hour heat exposure | Systolic and diastolic pressures measured in triplicate. |
| SDNN | Every hour during the 8-hour heat exposure | Standard deviation of normal-to-normal R-R intervals measured via 3-lead ECG. |
| RMSSD | Every hour during the 8-hour heat exposure | Root mean squared standard deviation of normal-to-normal R-R intervals measured via 3-lead ECG. |
| Rate pressure product | Every hour during the 8-hour heat exposure | Rate pressure product calculated as systolic blood pressure x heart rate. |
| Heart rate temperature (peak) | 8-hour heat exposure | Peak rectal temperature measured during the 8-hour heat exposure. |
| Stand test: 30:15 ratio | Prior to and following the 8-hour heat exposure | 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. |
| Stand test: Systolic response to standing | Prior to and following the 8-hour heat exposure | Fall in systolic blood pressure after standing from a supine position. |
| Baroreflex sensitivity | Prior to and following the 8-hour heat exposure | Baroreflex sensitivity determined during cyclic stand-squat manoeuvres. |
| Change in plasma volume | Prior to and following the 8-hour heat exposure | Change in plasma volume calculated from venous blood samples (Dill and Costill technique) |
| Body fluid loss | Every hour during the 8-hour heat exposure | Body fluid loss calculated as a change in body weight from pre-exposure values (corrected for food intake and deification). |
| Heart rate (AUC) | 8-hour heat exposure | Heart rate will be measured continuously throughout each exposure and the area under the curve will be calculated. |
Countries
Canada
Contacts
Primary ContactGlen P Kenny, PhD
Backup ContactRobert D Meade, PhD
Outcome results
None listed