Heat StressNCT06633302
Physiological Strain in Older Adults During a Simulated Heat Wave
A study testing Simulated multi-day heatwave exposure in people with Heat Stress and Physiological Stress, run by University of Ottawa at 1 site in Canada.
Trial summary
A recent report showed that maintaining indoor temperature at or below 26°C safeguards older, heat vulnerable adults against potentially dangerous increases in thermal and cardiovascular strain during an extreme heat event (PMID: 38329752). Read more about this study
- Who is it for?
- Ages 65 to 85 yearsHealthy volunteers can take part
- Conditions the study is for
- Heat Stress, Physiological Stress
- What is being tested?
- Simulated multi-day heatwave exposure
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 18 participants
- Where
- 1 siteCanada
- Study dates
- 15 Oct 2024to 21 May 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 65 to 85 years
- All sexes
- Healthy volunteers accepted
- Older adult
Who may be able to join
- Non-smoking.
- English or French speaking.
- Ability to provide informed consent.
- with or without a) chronic hypertension (elevated resting blood pressure; as defined by Heart and Stroke Canada and Hypertension Canada), b) type 2 diabetes as defined by Diabetes Canada, with at least 5 years having elapsed since time of diagnosis
Who cannot join
- Episode(s) of severe hypoglycemia (requiring the assistance of another person) within the previous year, or inability to sense hypoglycemia (hypoglycemia unawareness).
- Serious complications related to your diabetes (gastroparesis, renal disease, uncontrolled hypertension, severe autonomic neuropathy).
- Uncontrolled hypertension - BP >150 mmHg systolic or >95 mmHg diastolic in a sitting position.
- Restrictions in physical activity due to disease (e.g. intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.).
- Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
- Cardiac abnormalities identified during screening
Trial locations and contacts
1 site in 1 country.
About this study
Official title: Evaluating the Efficacy of a 26°C Indoor Temperature for Limiting Thermal and Cardiovascular Strain in Older Adults During a Simulated Multi-day Heat Event
A recent report showed that maintaining indoor temperature at or below 26°C safeguards older, heat vulnerable adults against potentially dangerous increases in thermal and cardiovascular strain during an extreme heat event (PMID: 38329752). However, this proposed limit does not consider the potential cumulative effect of successive days of heat exposure, which could lead to a progressive deterioration in thermoregulatory and cardiovascular function and necessitate adjustments to upper indoor temperature limits. Further, thermal comfort and quality of sleep may be negatively impacted when bedroom temperatures exceed 24°C (PMID: 3090680). On this basis, some health agencies have recommended that bedroom temperatures at night should not exceed 26°C unless ceiling fans are available (PMID: 3090680). Currently, however, it is unknown whether indoor overheating impairs sleep quality and physiological strain on a subsequent day in older adults and, if so, whether maintaining indoor temperature at 26°C is sufficient to prevent these adverse health impacts.
With rising global temperatures and more extreme heat events, energy management strategies to limit the strain on the power grid during the daytime are now increasingly commonplace. Thus, understanding the benefits of maintaining indoor temperature at the recommend upper limits of 26°C during the nighttime only on surrogate physiological indicators of health is an important step in understanding how to optimize protection for heat-vulnerable older adults when power outages occur.
The investigators will assess the efficacy of proposed indoor temperature limits (i.e., 26°C) in mitigating increases in core temperature and cardiovascular strain over three consecutive days (3 days, 2 nights) in older adults (60-85 years) with (indoor temperatures maintained at the recommend 26°C at all times throughout the three days) and without (daytime temperature fixed at 34°C (temperature experienced in homes without air-conditioning during an extreme heat event) with nighttime temperature at 26°C) access to daytime cooling. By quantifying the effect of daylong indoor overheating on surrogate physiological outcomes linked with heat-related mortality and morbidity in older adults, the investigators can determine if refinements in the recommended upper temperature threshold is required, including best practices when power outages may occur during an extreme heat event.
- Conditions
- Heat Stress, Physiological Stress
- Being tested
- Simulated multi-day heatwave exposure
- Keywords
- Heat wave, Indoor overheating, Indoor temperatures, Thermoregulation, Heat strain, Elderly, Heat vulnerability, Cardiovascular strain, Sleep, Hyperthermia, Fatigue
- Medical subject headings
- Heat Stress Disorders, Hyperthermia, Fatigue
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Simulated multi-day heatwave exposureOther
Older adults exposed to a multi-day simulated heat wave exposure
| Study group | Role | What they receive |
|---|---|---|
| Exposure to indoor temperature limits daylong | Experimental | Participants exposed to three consecutive days (3 days, 2 nights) in an indoor environment maintained at either 26°C at all times (condition A, recommended upper indoor temperature limits during an extreme heat event). Receives: Other: Simulated multi-day heatwave exposure |
| Exposure to indoor temperature limits nighttime only | Experimental | Participants exposed to three consecutive days (3 days, 2 nights) to indoor overheating during the daytime (34°C, temperatures experienced in homes without air-conditioning) (9:00 to 19:00) with nighttime (19:00 to 9:00) indoor temperatures reduced to the recommended limit of 26°C. Receives: Other: Simulated multi-day heatwave exposure |
What is being measured
The primary outcome is the main question the study is designed to answer.
Core temperature (Peak) during daytime
Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the daytime period of the simulated heat wave.
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Secondary outcomes (37)
Muscle oxygen during battery of cardiovascular, postural and cognitive tests during daytime
Participants will be attached with one probe placed on the left prefrontal cortex and one on the muscle belly of the vastus lateralis to measure tissue oxygenation using near-infrared spectroscopy (NIRS; Portalite, Artinis Medical, The Netherlands).
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Profiles of Mood States (POMS) during daytime
Potential changes in mood (7 subscales of mood: tension, anger, depression, fatigue, confusion, vigor and esteem-related affect). The POMS-40 is a validated, self-administered questionnaire that examines seven distinct aspects of mood state across two positive subscales (Esteem-Related Affect, and Vigor) and five negative subscales (Fatigue, Tension, Confusion, Anger, and Depression), which are described across 40 distinct adjectives. For each individual item, participants were asked to describe "how you feel right now" by responding using a 5-point Likert scale (0 = "Not at all", 1 = "A little", 2 = "Moderately", 3 = "Quite a lot", or 4 = "Extremely"). The values of items associated with a specific subscale (e.g., Fatigue) were summed to calculate its score.
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heart rate variability: RMSSD during nighttime
Root mean squared standard deviation of normal-to-normal R-wave to R-wave intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Heart rate variability: SDNN during nighttime
Standard deviation of normal-to-normal R-wave to R-wave intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Heat rate AUC during nighttime
Heart rate measured during each daytime exposure to simulated heat wave (15-min average)
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Heat rate peak during nighttime
Heart rate during each daytime exposure to simulated heat wave (15-min average)
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Core temperature end of nighttime
Rectal temperature measured at hour 10 of each daytime exposure to simulated heat wave (15-min average)
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Core temperature (AUC) during nighttime
Area under the curve of rectal temperature (in degree-hours)
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Core temperature (Peak) during nighttime
Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the daytime period of the simulated heat wave.
Measured: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Orthostatic intolerance symptoms assessment during daytime
Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance during the lying to standing tests. All symptoms scored on a scale from 0 (none) to 10 (worst possible) and include feelings of: (1) "dizziness, lightheadedness, feeling faint, or feeling like you might black out"; (2) "Problems with vision (blurring, seeing spots, tunnel vision, etc.)"; (3) "Weakness"; (4) "Fatigue"; (5) "Trouble concentrating"; and (6) "Head and neck discomfort".
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Arousal scale during daytime
Felt arousal scale assessed via a visual analog scale ("How worked up are you?") ranging from "high arousal" to "low arousal".
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Thirst sensation scale during daytime
Thirst sensation scale assessed via a visual analog scale ("How thirsty are you?") ranging from "Very, very thirsty" to "Not thirsty at all" (midpoint: moderately thirsty).
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Thermal sensation scale during daytime
Thermal sensation assessed via a visual analog scale ("How hot do you feel?") ranging from "extremely hot" to "neutral"(midpoint: hot)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Thermal comfort scale during daytime
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") ranging from "extremely uncomfortable" to "extremely comfortable"(midpoint: neutral).
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Change in plasma volume during daytime
Change in plasma volume from baseline values calculated from duplicate measurements of hemoglobin and hematocrit at the start and end of each exposure using the technique by Dill and Costill
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Fluid loss during daytime
Fluid loss calculated as the change in body mass during each exposure presented as a percentage of baseline body mass (corrected for food consumption)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Fluid consumption during daytime
Average hourly fluid consumption calculated by weighing participant water intake at the start and end of each hour of exposure (normalized to the exposure duration).
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heart rate variability: RMSSD during daytime
Root mean squared standard deviation of normal-to-normal R-wave to R-wave intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heart rate variability: SDNN during daytime
Standard deviation of normal-to-normal R-wave to R-wave intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Rate pressure product during daytime
Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate.
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Diastolic blood pressure during daytime
Diastolic blood pressure measured in triplicate via automated oscillometry (~60 seconds between measures)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Systolic blood pressure during daytime
Systolic blood pressure measured in triplicate via automated oscillometry (~60 seconds between measures)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Systolic Response to Standing From Supine during daytime
Systolic blood pressure response to standing evaluated as the difference in blood pressure measured between the standing and supine. Standing systolic blood pressure will be taken as the lowest value of those measured after 60 and 120 seconds of standing. Systolic response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest).
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
BTrackS Balance Assessment during daytime (Postural stability)
To assess postural stability, participants will be asked to stand on a BTracks force plate with their feet spread out to shoulder width, hand on their hips and eyes closed. The assessment will comprise of four trials (one practice trial) lasting 20 seconds in length and 20 seconds between trials. Center of pressure (COP) vector data along vertical (y) and horizontal (x) axes will be summed for the total path excursion length (cm) during each trial.
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
CDC 4-Stage Balance Test during daytime (Postural stability)
To assess postural stability, participants hold a tablet to their chest, then auditory cues guide participants through four consecutive stances, feet side by side, instep of one foot touching the big toe of the other foot, tandem stand with one foot in front of the other, heel touching toe, and stand on one foot. The balance assessment will be evaluated based on movement detected by an accelerometer integrated into the hardware of the tablet device (Sway Medical Inc).
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Executive function during daytime (cognitive function)
Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of executive function. Participants will complete the Cued Stroop test, in which they are presented a sequence of congruent, neutral and incongruent colour-word tasks.
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Memory recall during daytime (cognitive function)
Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of memory recall. Participants complete both a delayed recall test and a working memory test.
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Impulse control during daytime (cognitive function)
Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of impulse control. Participants will be asked to respond to both "go" and "no-go" visual cues. In response to the "go" cue, participants will initiate a movement of the device.
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Reaction time during daytime (cognitive function)
Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of reaction time. Participants will be asked to initiate a movement of the device in response to a visual cue.
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Cardiac response to standing from supine (30:15 Ratio) during daytime
Cardiac response to standing evaluated as the ratio between the highest R-wave to R-wave interval (lowest heart rate) measured at the 30th heart beat after standing from supine (+/- 5 beats) and the lowest R-wave to R-wave interval (highest heart rate) measured at the 15th heart beat after standing (+/- 5 beats). Cardiac response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest). Assessment is performed in the morning prior to and following daytime exposure.
Measured: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heat rate AUC during daytime
Heart rate measured during each daytime exposure to simulated heat wave (15-min average)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heat rate peak during daytime
Heart rate during each daytime exposure to simulated heat wave (15-min average)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Core temperature end of daytime exposure
Rectal temperature measured at hour 10 of each daytime exposure to simulated heat wave (15-min average)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Core temperature (AUC) during daytime
Area under the curve of rectal temperature (in degree-hours)
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Environmental Symptoms Questionnaire (ESQ)
Self-reported environmental reactions and medical symptomatology associated with prolonged heat exposure. The ESQ-IV is a validated 68-item, self-administered questionnaire that has been used successfully in identifying symptomatology during exposure to a wide variety of environmental conditions, including heat exposure [24, 25]. Participants are asked to assess and described "how you have been feeling today" by responding to each item using a 6-point Likert scale (0 = "Not at all", 1 = "Slight", 2 = "Somewhat", 3 = "Moderate", 4 = "Quite a bit", or 5 = "Extreme"). Total Symptom Score was calculated from this data by taking the sum of the intensity ratings from all 68 individual items using reverse scores for the three positive items from the list ("I Felt Good", "I Felt Alert", and "I Felt Wide Awake").
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Sleep quality and quantify assessment
The following questionnaires will be administered:
Consensus Sleep Diary (CSD) to provide an overview of the sleep quantity and quality of the previous night.
Richards-Campbell Sleep Questionnaire to evaluate the perception of sleep .
Leeds Sleep evaluation questionnaire which is 10-item, subjective, questionnaire designed to assess changes in sleep quality over the course of the intervention.
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Sleepiness during daytime
The following questionnaires will be administered to evaluate the participants sleepiness during the daytime exposure period:
Karolinska sleepiness scale measures the subjective level of sleepiness at a particular time during the day.
Stanford sleepiness scale consists of only one item, where participant must identify one of seven statements that best represents their level of perceived sleepiness
Measured: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted9 Oct 2024
- Study start15 Oct 2024
- Primary completion21 May 2025
- Study completion21 May 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for Heat StressStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Masking
- Single blind
- Who is masked
- Outcomes assessor
- Enrolment
- 18 participants (actual)
Sponsor and investigators
- Lead sponsor
- University of Ottawa
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Glen P. Kenny, University of Ottawa
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06633302
- Sponsor's protocol ID
- HEPRU-2024-08-A
- Status last verified
- Mar 2026
- First submitted
- 4 Oct 2024
- Last updated
- 27 Mar 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
Publications
Meade RD, King KE, McCormick JJ, Taggart SM, Bourgois G, Goulet N, Li-Maloney C, Boulay P, Sigal RJ, Kenny GP. Effects of a 3-day simulated heatwave on physiological and functional outcomes in older adults in Canada: a single-site randomised crossover trial. Lancet Planet Health. 2027 Jul 28:101517. doi: 10.1016/j.lanplh.2026.101517. Online ahead of print.
PubMed 42815509
Study at a glance
From the registry record, last updated by the sponsor on 27 Mar 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Evaluating the Efficacy of a 26°C Indoor Temperature for Limiting Thermal and Cardiovascular Strain in Older Adults During a Simulated Multi-day Heat Event
- ClinicalTrials.gov ID
- NCT06633302
- Acronym / sponsor ID
- HEPRU-2024-08-A
- Conditions
- Heat Stress, Physiological Stress
- Keywords
- Heat wave, Indoor overheating, Indoor temperatures, Thermoregulation, Heat strain, Elderly, Heat vulnerability, Cardiovascular strain
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 18 participants (actual)
- Lead sponsor
- University of OttawaUniversity, hospital or other
- Study start
- 15 Oct 2024 (actual)
- Primary completion
- 21 May 2025 (actual)
- Study completion
- 21 May 2025 (actual)
- First posted
- 9 Oct 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
A recent report showed that maintaining indoor temperature at or below 26°C safeguards older, heat vulnerable adults against potentially dangerous increases in thermal and cardiovascular strain during an extreme heat event (PMID: 38329752). However, this proposed limit does not consider the potential cumulative effect of successive days of heat exposure, which could lead to a progressive deterioration in thermoregulatory and cardiovascular function and necessitate adjustments to upper indoor temperature limits. Further, thermal comfort and quality of sleep may be negatively impacted when bedroom temperatures exceed 24°C (PMID: 3090680). On this basis, some health agencies have recommended that bedroom temperatures at night should not exceed 26°C unless ceiling fans are available (PMID: 3090680). Currently, however, it is unknown whether indoor overheating impairs sleep quality and physiological strain on a subsequent day in older adults and, if so, whether maintaining indoor temperature at 26°C is sufficient to prevent these adverse health impacts.
With rising global temperatures and more extreme heat events, energy management strategies to limit the strain on the power grid during the daytime are now increasingly commonplace. Thus, understanding the benefits of maintaining indoor temperature at the recommend upper limits of 26°C during the nighttime only on surrogate physiological indicators of health is an important step in understanding how to optimize protection for heat-vulnerable older adults when power outages occur.
The investigators will assess the efficacy of proposed indoor temperature limits (i.e., 26°C) in mitigating increases in core temperature and cardiovascular strain over three consecutive days (3 days, 2 nights) in older adults (60-85 years) with (indoor temperatures maintained at the recommend 26°C at all times throughout the three days) and without (daytime temperature fixed at 34°C (temperature experienced in homes without air-conditioning during an extreme heat event) with nighttime temperature at 26°C) access to daytime cooling. By quantifying the effect of daylong indoor overheating on surrogate physiological outcomes linked with heat-related mortality and morbidity in older adults, the investigators can determine if refinements in the recommended upper temperature threshold is required, including best practices when power outages may occur during an extreme heat event.
Study design
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Masking
- Single blind (outcomes assessor)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Exposure to indoor temperature limits daylong | Experimental | Other: Simulated multi-day heatwave exposureParticipants exposed to three consecutive days (3 days, 2 nights) in an indoor environment maintained at either 26°C at all times (condition A, recommended upper indoor temperature limits during an extreme heat event). |
| Exposure to indoor temperature limits nighttime only | Experimental | Other: Simulated multi-day heatwave exposureParticipants exposed to three consecutive days (3 days, 2 nights) to indoor overheating during the daytime (34°C, temperatures experienced in homes without air-conditioning) (9:00 to 19:00) with nighttime (19:00 to 9:00) indoor temperatures reduced to the recommended limit of 26°C. |
Who may qualify
- Ages
- 65 to 85 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Older adult
Key inclusion criteria (4 listed)
- Non-smoking.
- English or French speaking.
- Ability to provide informed consent.
- with or without a) chronic hypertension (elevated resting blood pressure; as defined by Heart and Stroke Canada and Hypertension Canada), b) type 2 diabetes as defined by Diabetes Canada, with at least 5 years having elapsed since time of diagnosis
Key exclusion criteria (6 listed)
- Episode(s) of severe hypoglycemia (requiring the assistance of another person) within the previous year, or inability to sense hypoglycemia (hypoglycemia unawareness).
- Serious complications related to your diabetes (gastroparesis, renal disease, uncontrolled hypertension, severe autonomic neuropathy).
- Uncontrolled hypertension - BP >150 mmHg systolic or >95 mmHg diastolic in a sitting position.
- Restrictions in physical activity due to disease (e.g. intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.).
- Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Simulated multi-day heatwave exposureOlder adults exposed to a multi-day simulated heat wave exposure | Other | Exposure to indoor temperature limits daylong, Exposure to indoor temperature limits nighttime only |
Primary outcome
Core temperature (Peak) during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the daytime period of the simulated heat wave.
37 secondary outcomes
Muscle oxygen during battery of cardiovascular, postural and cognitive tests during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Profiles of Mood States (POMS) during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heart rate variability: RMSSD during nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Heart rate variability: SDNN during nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Heat rate AUC during nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Heat rate peak during nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Core temperature end of nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Core temperature (AUC) during nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Core temperature (Peak) during nighttime
Time frame: End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)
Orthostatic intolerance symptoms assessment during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Arousal scale during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Thirst sensation scale during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Thermal sensation scale during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Thermal comfort scale during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Change in plasma volume during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Fluid loss during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Fluid consumption during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heart rate variability: RMSSD during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heart rate variability: SDNN during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Rate pressure product during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Diastolic blood pressure during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Systolic blood pressure during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Systolic Response to Standing From Supine during daytime
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
BTrackS Balance Assessment during daytime (Postural stability)
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
CDC 4-Stage Balance Test during daytime (Postural stability)
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Executive function during daytime (cognitive function)
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Memory recall during daytime (cognitive function)
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Impulse control during daytime (cognitive function)
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Reaction time during daytime (cognitive function)
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Cardiac response to standing from supine (30:15 Ratio) during daytime
Time frame: At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heat rate AUC during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Heat rate peak during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Core temperature end of daytime exposure
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Core temperature (AUC) during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Environmental Symptoms Questionnaire (ESQ)
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Sleep quality and quantify assessment
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Sleepiness during daytime
Time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 27 Mar 2026.
- Derived from this study: PubMed 42815509Meade RD, King KE, McCormick JJ, Taggart SM, Bourgois G, Goulet N, Li-Maloney C, Boulay P, Sigal RJ, Kenny GP. Effects of a 3-day simulated heatwave on physiological and functional outcomes in older adults in Canada: a single-site randomised crossover trial. Lancet Planet Health. 2027 Jul 28:101517. doi: 10.1016/j.lanplh.2026.101517. Online ahead of print.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Simulated multi-day heatwave exposure in people with Heat Stress and Physiological Stress, run by University of Ottawa at 1 site in Canada.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 6 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 27 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Canada. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Core temperature (Peak) during daytime (time frame: End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT06633302, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 27 Mar 2026.