Physiological Responses in Young and Older Adults During a Prolonged Simulated Heatwave

NCT04353076 | Completed

• 1 other identifier: H 05-16-07
• Study Type: interventional
• Target: 60
• Locations: 1 country
• Sites: 1

Brief Summary

Climate change not only affects the planet's natural resources, but also severely impacts human health. An individual's ability to adequately cope with short- or long-term increases in ambient temperature is critical for maintaining health and wellbeing. Prolonged increases in temperature (heatwaves) pose a serious health risk for older adults, who have a reduced capacity to efficiently regulate body temperature. However, information regarding the impact of age on body temperature regulation during prolonged exposure to extreme heat is lacking, as is research on the effectiveness of interventions aimed at reducing heat strain in such situations. This project will address these important knowledge gaps by exposing healthy young and older adults to a prolonged (9 hour) heat exposure, with conditions representative of heatwaves in temperate continental climates. An additional cohort of older adults will complete the same heatwave simulation but will be briefly (2 hours) exposed to cooler conditions (22-23°C) mid-way through the session (akin to visiting a cooling centre or cooled location). The investigators will evaluate age-related differences in the capacity to dissipate heat via direct air calorimetry (a unique device that permits the precise measurement of the heat dissipated by the human body) and their effect on the regulation of body temperature. The investigators anticipate that older adults will exhibit progressive increases in the heat stored in the body throughout the simulated heatwave, resulting in progressive increases in body core temperature. Further, older adults exposed to brief-mid day cooling will rapidly gain heat upon re-exposure to high ambient temperatures. As a result, by the end of exposure body temperatures will be similar to the group not removed from the heat.

Conditions

Aging; Heat Stress; Physiological Stress

Keywords

Heatwave; Heat-vulnerability; Cooling center; Heat strain; Cardiovascular responses

Outcome Measures

Primary Outcomes (4)

• Body heat storage

  Cumulative amount of heat stored within the body

  First 3 hours (hours 1-3) of simulated heatwave

• Body heat storage

  Cumulative amount of heat stored within the body

  Final 3 hours (hours 7-9) of simulated heatwave

• Rectal temperature

  Index of core body temperature

  Hour 3 of simulated heatwave

• Rectal temperature

  Index of core body temperature

  Hour 9 of simulated heatwave

Secondary Outcomes (19)

• Heart rate

  Hour 3 of simulated heatwave

• Heart rate

  Hour 9 of simulated heatwave

• Systolic blood pressure

  Hour 3 of simulated heatwave

• Systolic blood pressure

  Hour 9 of simulated heatwave

• Diastolic blood pressure

  Hour 3 of simulated heatwave

Study Arms (3)

Young adults

EXPERIMENTAL

Young adults exposed to a 9-hour simulated heatwave (40°C, 15% relative humidity)

Other: Simulated heatwave exposure

Older adults (no cooling)

EXPERIMENTAL

Older adults exposed to a 9-hour simulated heatwave (40°C, 15% relative humidity)

Other: Simulated heatwave exposure

Older adults (cooling)

EXPERIMENTAL

Older adults exposed to a 9-hour simulated heatwave (40°C, 15% relative humidity) with ambient cooling intervention (i.e., exposure to an air-conditioned room) for hours 5-6.

Other: Simulated heatwave exposure with mid-day cooling

Interventions

Simulated heatwave exposure OTHER

Young and older adults (no cooling) are exposed to a 9-hour simulated exposure.

Older adults (no cooling); Young adults

Simulated heatwave exposure with mid-day cooling OTHER

Older adults (cooling) are exposed to a 9-hour simulated exposure with mid-day ambient cooling.

Older adults (cooling)

Eligibility Criteria

• Age: 18 Years - 80 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• male or female (non-pregnant) adults 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 and or c) obesity as defined by the World Health Organization (Body Mass Index \[BMI\] greater than or equal to 30).
• non-smoking.

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 in your physical health screening form (adults \<65 years of age and older; adults \<60 years of age and older with diabetes and or hypertension) or during exercise stress testing as assessed by 12-lead (all adults ≥65 years of age and older).

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N6N5, Canada

Location

Related Publications (3)

• Journeay WS, McCormick JJ, King KE, Garrett JM, O'Connor FK, Hutchins KP, Meade RD, Kenny GP. Serum endothelial monocyte-activating polypeptide-II response after 9 h of passive heat exposure: influence of age, diabetes, or hypertension. Am J Physiol Regul Integr Comp Physiol. 2026 Feb 1;330(2):R119-R125. doi: 10.1152/ajpregu.00307.2025. Epub 2026 Jan 9.

  PMID: 41512819 DERIVED

• Garrett JM, McCormick JJ, King KE, Meade RD, Boulay P, Sigal RJ, O'Connor FK, Kenny GP. Irisin and betatrophin responses to 9 h of passive heat exposure: Influence of age, hypertension, and type 2 diabetes. Physiol Rep. 2025 Jun;13(12):e70411. doi: 10.14814/phy2.70411.

  PMID: 40554659 DERIVED

• Lee B, Meade R, Davey S, Thake C, McCormick J, King K, Kenny GP. Effect of brief ambient cooling on serum stress biomarkers in older adults during a daylong heat exposure: a laboratory-based heat wave simulation. Appl Physiol Nutr Metab. 2025 Jan 1;50:1-8. doi: 10.1139/apnm-2024-0476.

  PMID: 40036754 DERIVED

MeSH Terms

Conditions

Heat Stress Disorders

Condition Hierarchy (Ancestors)

Wounds and Injuries

Study Officials

• Glen P Kenny, PhD

  University of Ottawa

  PRINCIPAL INVESTIGATOR

• Ronald J Sigal, MD, MPH

  University of Calgary

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NON RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Full Professor, University Research Chair

Study Record Dates

• First Submitted: April 13, 2020
• First Posted: April 20, 2020
• Study Start: January 1, 2019
• Primary Completion: April 2, 2021
• Study Completion: April 2, 2021
• Last Updated: August 18, 2021

Record last verified: 2021-08

Data Sharing

• IPD Sharing: Will not share

Locations

CA (1)