Enhancing Heat Resiliency in Older Adults During Indoor Overheating Via Heat Acclimation by Warm Water Immersion

NCT ID: NCT06670365

Last Updated: 2025-06-15

Basic Information

• Recruitment Status: RECRUITING
• Clinical Phase: NA
• Total Enrollment: 12 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2024-11-11
• Study Completion Date: 2025-12-31

Brief Summary

As overheating in buildings is expected to increase as global warming continues, proactive measures to increase heat resiliency in heat-vulnerable older people are needed, especially for those without access to home cooling or reliable sources of electricity. While short-term heat acclimation through exercise in the heat has been shown to increase heat dissipation and decrease both the physical and mental stress imposed on individuals exposed to heat, such protocols are not tenable for older, sedentary adults. A recent report showed that seven consecutive days of warm-water immersion improved whole-body heat loss and reduced physiological strain as assessed during an exercise-heat stress in habitually active older men This represents a critical finding as an increase heat-loss capacity would serve as an important safeguard for older adults exposed to indoor overheating due to lack of air-conditioning. While this preliminary data highlights passive hot water immersion as a promising strategy for increasing heat-resilience in vulnerable adults, work is needed to confirm its efficacy in more "real-world" environments. Thus, this study aims to assess the effectiveness of a 7-day passive heating (warm-water immersion with core temperature clamped at ~38.5°C for the final 60 minutes) protocol in mitigating increases in thermal and cardiovascular strain in older females exposed to daylong (10-hours) indoor overheating (36°C, 45% relative humidity) prior to and following the passive heating intervention. Relative to males, females have a reduced heat loss capacity (~5%), which is driven by differences in the activation of heat loss responses (i.e., skin blood flow and sweating). Although there have been mixed findings with regards to the influence of sex as a mediating factor for heat-related mortality, some studies suggest that females are at a higher risk of heat-related mortality and morbidity compared to males, especially amongst older individuals (≥65 years). Notably, a greater proportion of older females died compared to their male counterparts during the 2021 Western Heat Dome. While the underlying causes for these differences remain unclear, greater cardiovascular strain may place females at higher mortality risk during extreme heat.

Conditions

Hyperthermia; Thermoregulation; Aging; Heat Acclimation and Thermotolerance

Study Design

• Allocation Method: NA
• Intervention Model: SINGLE_GROUP
• Primary Study Purpose: BASIC_SCIENCE
• Blinding Strategy: NONE

Study Groups

Daylong exposure to indoor overheating

Prior to and following the warm-water immersion protocol, participants will undergo a 10-hour passive heat exposure where they will remain in a climate-controlled chamber regulated at 36°C and 45% humidity (temperatures experienced indoors during extreme heat events in North America). During this time they will remain seated with the exception of hourly 5-minute breaks to stretch.

Group Type: EXPERIMENTAL

Heat acclimation by warm-water immersion

Intervention Type: OTHER

Participants will be immersed in a whirlpool tub to the shoulder level in a circulated water bath maintained at \~40°C until their core temperature achieves a steady-state of 38.5°C for 60 minutes. The warm-water immersion protocol will be repeated for 6 more consecutive days.

Interventions

Heat acclimation by warm-water immersion

Participants will be immersed in a whirlpool tub to the shoulder level in a circulated water bath maintained at \~40°C until their core temperature achieves a steady-state of 38.5°C for 60 minutes. The warm-water immersion protocol will be repeated for 6 more consecutive days.

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 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

• Minimum Eligible Age: 65 Years
• Maximum Eligible Age: 85 Years
• Eligible Sex: FEMALE
• Accepts Healthy Volunteers: Yes

Sponsors

University of Ottawa

OTHER

Sponsor Role: lead

Responsible Party

Glen P. Kenny

Professor

Responsibility Role: PRINCIPAL_INVESTIGATOR

Principal Investigators

Glen P Kenny, PhD

Role: PRINCIPAL_INVESTIGATOR

University of Ottawa

Locations

University of Ottawa

Ottawa, Ontario, Canada

Site Status: RECRUITING

Countries

Canada

Central Contacts

Glen P Kenny, PhD

Role: CONTACT

gkenny@uottawa.ca

613-562-5800 ext. 4282

Caroline Li-Maloney, MSc

Role: CONTACT

cmalo020@uottawa.ca

Facility Contacts

Glen P Kenny, PhD

Role: primary

gkenny@uottawa.ca

613-562-5800 ext. 4282

Caroline Li-Maloney, MSc

Role: backup

cmalo020@uottawa.ca

Other Identifiers

HEPRU-2024-09-A

Identifier Type: -

Identifier Source: org_study_id