Clinical trial NCT06842953: Influence of Indoor Humidity on Physiological Strain in Older Adults During a Simulated Heat Wave
Official title: Is an Adjustment in the Recommended Indoor Temperature Upper Limit of 26°C Required During Higher Levels of Humidity?
Study type: INTERVENTIONAL
Overall status: RECRUITING
Phase: NA
Conditions: Heat Stress
Physiological Stress
Keywords: Heat wave
Indoor overheating
Thermoregulation
Heat strain
Elderly
Heat vulnerability
Hyperthermia
Thermal comfort
Lead sponsor: University of Ottawa
Sponsor class: OTHER
First posted: 2025-02-24
Enrollment: 10
Sex: ALL
Minimum age (years): 60
Maximum age (years): 85
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: yes
Allocation: RANDOMIZED
Intervention model: CROSSOVER
Primary purpose: BASIC_SCIENCE

Brief summary: 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: Inclusion Criteria:

* 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

Exclusion Criteria:

* 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.).
* Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
* Cardiac abnormalities identified during screening

Primary outcomes:
measure: Core temperature (Peak) during daylong exposure to indoor overheating
timeFrame: End of 10 hour daylong exposure
measure: Core temperature (AUC) during daylong exposure to indoor overheating
timeFrame: End of 10 hour daylong exposure
measure: Heat rate (Peak) during daylong exposure to indoor overheating
timeFrame: End of 10 hour daylong exposure
measure: Heart rate (AUC) during daylong exposure to indoor overheating
timeFrame: End of 10 hour daylong exposure
measure: Cardiac response to standing from supine (30:15 Ratio) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Systolic Response to Standing From Supine during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Heart rate variability: RMSSD during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Heart rate variability: SDNN during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Thermal comfort scale during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Thirst sensation scale during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Arousal scale during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Fluid loss during daylong exposure to indoor overheating
timeFrame: At end of 10 hour daylong exposure
measure: Changes in plasma volume during daylong exposure to indoor overheating
timeFrame: At end of 10 hour daylong exposur
measure: Systolic blood pressure during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Rate pressure product during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
Secondary outcomes:
measure: Impulse control (cognitive function) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Memory recall (cognitive function) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: CDC 4-Stage Balance Test (Postural stability) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: BTrackS Balance Assessment (Postural stability) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Profiles of Mood States (POMS) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Environmental Symptoms Questionnaire (ESQ) during daylong exposure to indoor overheating
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Sleepiness during daylong exposure to indoor overheating A
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
measure: Sleepiness during daylong exposure to indoor overheating B
timeFrame: At the start (hour 0) and end of 10 hour daylong exposure
Other outcomes:
Locations:
city: Ottawa
country: Canada
facility: University of Ottawa
state: Ontario
Study officials:
References: