Physiological Strain in Older Adults During a Simulated Heat Wave

NCT06633302 | Completed

• 1 other identifier: HEPRU-2024-08-A
• Study Type: interventional
• Target: 18
• Locations: 1 country
• Sites: 1

Brief 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). 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

Keywords

Heat wave; Indoor overheating; Indoor temperatures; Thermoregulation; Heat strain; Elderly; Heat vulnerability; Cardiovascular strain; Sleep; Hyperthermia; Fatigue

Outcome Measures

Primary Outcomes (1)

• 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.

  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

  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

  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

  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

  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

  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)

Study Arms (2)

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).

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.

Other: Simulated multi-day heatwave exposure

Interventions

Simulated multi-day heatwave exposure OTHER

Older adults exposed to a multi-day simulated heat wave exposure

Exposure to indoor temperature limits daylong; Exposure to indoor temperature limits nighttime only

Eligibility Criteria

• Age: 65 Years - 85 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Older Adult (65+)

You may qualify if:

• 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

You may not qualify if:

• 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

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N1A2, Canada

Location

MeSH Terms

Conditions

Heat Stress Disorders; Hyperthermia; Fatigue

Condition Hierarchy (Ancestors)

Wounds and Injuries; Body Temperature Changes; Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Professor

Study Record Dates

• First Submitted: October 4, 2024
• First Posted: October 9, 2024
• Study Start: October 15, 2024
• Primary Completion: May 21, 2025
• Study Completion: May 21, 2025
• Last Updated: March 27, 2026

Record last verified: 2026-03

Locations

CA (1)