Influence of Indoor Humidity on Physiological Strain in Older Adults During a Simulated Heat Wave

NCT ID: NCT06842953

Last Updated: 2025-06-15

Basic Information

• Recruitment Status: RECRUITING
• Clinical Phase: NA
• Total Enrollment: 10 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2025-03-14
• Study Completion Date: 2026-09-01

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.

Conditions

Heat Stress; Physiological Stress

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: CROSSOVER
• Primary Study Purpose: BASIC_SCIENCE
• Blinding Strategy: SINGLE

Study Groups

Exposure to recommended indoor temperature limit with normal indoor humidity

Participants exposed daylong (10 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Group Type: EXPERIMENTAL

Simulated indoor overheating

Intervention Type: OTHER

Older adults are exposed to a 10-hour simulated exposure

Exposure to recommended indoor temperature limit with low indoor humidity

Participants exposed daylong (10 hours) to an indoor temperature maintained at 26°C and 15% relative humidity (humidex equivalent of 23).

Group Type: EXPERIMENTAL

Simulated indoor overheating

Intervention Type: OTHER

Older adults are exposed to a 10-hour simulated exposure

Exposure to recommended indoor temperature limit with high indoor humidity

Participants exposed daylong (10 hours) to an indoor temperature maintained at 26°C and 85% relative humidity (humidex equivalent of 37).

Group Type: EXPERIMENTAL

Simulated indoor overheating

Intervention Type: OTHER

Older adults are exposed to a 10-hour simulated exposure

Exposure to high indoor temperature with normal indoor humidity

Participants exposed daylong (10 hours) to an indoor temperature maintained at 31°C and 45% relative humidity (humidex equivalent of 37).

Group Type: EXPERIMENTAL

Simulated indoor overheating

Intervention Type: OTHER

Older adults are exposed to a 10-hour simulated exposure

Interventions

Simulated indoor overheating

Older adults are exposed to a 10-hour simulated exposure

Intervention Type: OTHER

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

• Minimum Eligible Age: 60 Years
• Maximum Eligible Age: 85 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

University of Ottawa

OTHER

Sponsor Role: lead

Responsible Party

Glen P. Kenny

Full Professor

Responsibility Role: PRINCIPAL_INVESTIGATOR

Locations

University of Ottawa

Ottawa, Ontario, Canada

Site Status: RECRUITING

Countries

Canada

Central Contacts

Glen P Kenny, PhD

Role: CONTACT

gkenny@uottawa.ca

6135625800 ext. 4282

Facility Contacts

Glen P Kenny, PhD

Role: primary

gkenny@uottawa.ca

6135625800 ext. 4282

Other Identifiers

HEPRU-2025-02-A

Identifier Type: -

Identifier Source: org_study_id