Influence of Indoor Humidity on Physiological Strain in Older Adults During a Simulated Heat Wave
Trial statusRecruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age60-85
SponsorUniversity of Ottawa
About this trial
Laboratory-based studies show that exposure to high humidity can worsen the effects of heat stress in young and older adults by impeding sweat evaporation - the main mechanism by which the human body cools itself. At high levels of humidity, the efficiency of sweating decreases causing a greater rise core temperature and burden on the cardiovascular system. In this context, increasing temperatures and humidity with climate change thus pose a potential compound risk for human health. While humidity's role in heat-health outcomes could substantially alter projections of health burdens from climate change, the impact of humidity on physiological strain in vulnerable people in relation to the indoor environment has yet to be evaluated. In a recent study delineating the physiological effects of the proposed 26°C indoor upper limit (PMID: 38329752), relative humidity was set to 45% in all conditions based on indoor humidity standards by the American Society of Heating and Air-Conditioning Engineers. However, it is unknown whether a refinement of the recommended indoor temperature limit of 26°C is required in situations where humidity cannot be maintained at this level.
On separate occasions, the investigators will assess the change in body temperature and cardiovascular strain in older adults (65-85 years) exposed for 10 hours at the recommended indoor temperature limit of 26°C and 45% relative humidity (equivalent humidex of 29 (considered comfortable)) (experimental condition A), to 26°C with a relative humidity of 15% (equivalent humidex of 23 (considered comfortable); humidex is used to measure the perceived temperature taking into account the humidity)) (experimental condition B), to 26°C with a relative humidity of 85% (equivalent humidex of 37 (considered somewhat uncomfortable)) (experimental condition C), and to 31°C and 45% relative humidity with an equivalent humidex of 37 (considered somewhat uncomfortable) that is similar to experimental condition C. With this experimental design, investigators will assess the effects of indoor humidity in driving human heat strain and identify whether refinements in the recommended 26°C indoor temperature limit may be required. Further, by evaluating changes in relation to ambient conditions with a similar humidex, the investigators can assess how individuals perceive and respond to both heat and humidity.
Eligibility criteria
This trial accepts healthy volunteersQualifiers
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
Disqualifiers
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 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.).
Trial design
Design model
Crossover
Treatments tested in this trial
Simulated indoor overheating
Other interventionOlder adults are exposed to a 10-hour simulated exposure
Treatment groups
10 Participants
are divided into 4 treatment groupsGroup A: Exposure to recommended indoor temperature limit with normal indoor humidityExperimental treatment 1 intervention
Group B: Exposure to recommended indoor temperature limit with low indoor humidityExperimental treatment 1 intervention
Group C: Exposure to recommended indoor temperature limit with high indoor humidityExperimental treatment 1 intervention
Group D: Exposure to high indoor temperature with normal indoor humidityExperimental treatment 1 intervention
Trial outcomes
Primary outcomes
1
Core temperature (Peak) during daylong exposure to indoor overheating
Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the 10 hours of the simulated indoor overheating.
Time frame
End of 10 hour daylong exposure2
Core temperature (AUC) during daylong exposure to indoor overheating
Areas under the curve (AUC) of rectal temperature during the 10 hour simulate indoor overheating.
Time frame
End of 10 hour daylong exposure3
Heat rate (Peak) during daylong exposure to indoor overheating
Peak heart rate (15 min average) during exposure. Heart rate is measured continuously throughout the 10 hours of the simulated indoor overheating.
Time frame
End of 10 hour daylong exposure4
Heart rate (AUC) during daylong exposure to indoor overheating
Areas under the curve (AUC) of heart rate during the 10 hour simulate indoor overheating.
Time frame
End of 10 hour daylong exposureSecondary outcomes
1
Impulse control (cognitive function) during daylong exposure to indoor overheating
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.
Time frame
At the start (hour 0) and end of 10 hour daylong exposure2
Memory recall (cognitive function) during daylong exposure to indoor overheating
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.
Time frame
At the start (hour 0) and end of 10 hour daylong exposure3
CDC 4-Stage Balance Test (Postural stability) during daylong exposure to indoor overheating
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).
Time frame
At the start (hour 0) and end of 10 hour daylong exposure4
BTrackS Balance Assessment (Postural stability) during daylong exposure to indoor overheating
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.
Time frame
At the start (hour 0) and end of 10 hour daylong exposureSponsors and contacts
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Source ClinicalTrials.gov