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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).
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Extreme heat event simulation + no cooling (control) | Experimental | Adults aged 60-85 years with or without type 2 diabetes and/or hypertension |
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| Extreme heat event simulation + recommended cooling | Experimental | Adults aged 60-85 years with or without type 2 diabetes and/or hypertension |
|
| Extreme heat event simulation + hybrid cooling | Experimental | Adults aged 60-85 years with or without type 2 diabetes and/or hypertension |
|
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| No cooling (control) | Other | Participants are exposed to 35°C, 60% relative humidity for 8 hours. |
|
| Measure | Description | Time Frame |
|---|---|---|
| Core temperature (peak) | Peak rectal temperature measured during the 8-hour heat exposure. | 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. | 8-hour heat exposure |
| Measure | Description | Time Frame |
|---|---|---|
| Heart rate temperature (peak) | Peak rectal temperature measured during the 8-hour heat exposure. | 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. |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Glen P Kenny, PhD | Contact | 6135625800 | 4282 | gkenny@uottawa.ca |
| Robert D Meade, PhD | Contact | 6136986071 | rmead015@uottawa.ca |
| Name | Affiliation | Role |
|---|---|---|
| Glen P Kenny, PhD | University of Ottawa | Principal Investigator |
| Ronald J Sigal, MD, MPH | University of Calgary | Principal Investigator |
| Robert D Meade, PhD |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| University of Ottawa | Ottawa | Ontario | K1N6N5 | Canada |
Deidentified participant data will be available from Dr. Kenny upon reasonable request and signed access agreement.
After study completion
Reasonable request and signed access agreement
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| ID | Term |
|---|---|
| D000084462 | Hyperthermia |
| D006973 | Hypertension |
| D018882 | Heat Stress Disorders |
| ID | Term |
|---|---|
| D001832 | Body Temperature Changes |
| D012816 | Signs and Symptoms |
| D013568 | Pathological Conditions, Signs and Symptoms |
| D014947 | Wounds and Injuries |
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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)
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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.
| Recommended cooling | Other | 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. |
|
| Hybrid cooling | Other | 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 |
|
| 8-hour heat exposure |
| Mean skin temperature | Mean skin temperature calculated as a weighted average of skin temperatures at 8 body regions. | Before and continuously throughout each 8 hour exposure |
| Arterial blood pressures | Systolic and diastolic pressures measured in triplicate. | Every hour during the 8-hour heat exposure |
| SDNN | Standard deviation of normal-to-normal R-R intervals measured via 3-lead ECG. | 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. | Every hour during the 8-hour heat exposure |
| Rate pressure product | Rate pressure product calculated as systolic blood pressure x heart rate. | 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). | 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. | 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. | Prior to and following the 8-hour heat exposure |
| Baroreflex sensitivity | Baroreflex sensitivity determined during cyclic stand-squat manoeuvres. | 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) | Prior to and following the 8-hour heat exposure |
| University of Ottawa |
| Principal Investigator |
| D014652 | Vascular Diseases |
| D002318 | Cardiovascular Diseases |