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

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

Interventions

OTHER

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.

Sponsors & Collaborators

• University of Ottawa

  lead OTHER

Principal Investigators

• Glen P Kenny, PhD · University of Ottawa

Study Design

Allocation

NA

Purpose

BASIC_SCIENCE

Masking

NONE

Model

SINGLE_GROUP

Eligibility

Min Age

65 Years

Max Age

85 Years

Sex

FEMALE

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2024-11-11

Primary Completion

2025-12-31

Completion

2025-12-31

Countries

• Canada

Study Locations