Clinical trial NCT05838612: Hot Water Immersion as a Heat Acclimation Strategy in Older Adults
Official title: Short-term Warm Water Immersion as a Heat Acclimation Strategy to Enhance Heat Dissipation in Older Adults: An Exploratory Study
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Hyperthermia
Heat Exposure
Heat Stress
Thermoregulation
Aging
Keywords: Thermoregulation
Warm-water immersion
Heat acclimation
Aging
Lead sponsor: University of Ottawa
Sponsor class: OTHER
First posted: 2023-05-01
Enrollment: 12
Sex: MALE
Minimum age (years): 60
Maximum age (years): 80
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: yes
Allocation: NA
Intervention model: SINGLE_GROUP
Intervention model description: Each participant will complete seven consecutive experimental sessions consisting of a passive heat acclimation involving a one hour immersion in warm water (\~40°C) with core temperature clamped at 38.5°C. Prior to and following the passive heat acclimation protocol, study participants will perform an exercise-heat stress test (Days 0 and 8) to assess whole-body heat loss in a hot-dry environment (40°C, 15% relative humidity). The exercise protocol will consist of three successive 30-minute bouts of exercise performed at increasing rates of metabolic heat production (i.e., 150, 200 and 250 W/m2), each separated by a 15-minute rest break, with the final recovery 1-hour in duration.
Primary purpose: BASIC_SCIENCE

Brief summary: Aging is associated with impairments in heat loss responses of skin blood flow and sweating leading to reductions in whole-body heat loss. Consequently, older adults store more body heat and experience greater elevations in core temperature during heat exposure at rest and during exercise. This maladaptive response occurs in adults as young as 40 years of age. Recently, heat acclimation associated with repeated bouts of exercise in the heat performed over 7 successive days has been shown to enhance whole-body heat loss in older adults, leading to a reduction in body heat storage. However, performing exercise in the heat may not be well tolerated or feasible for many older adults. Passive heat acclimation, such as the use of warm-water immersion may be an effective, alternative method to enhance heat-loss capacity in older adults. Thus, the following study aims to assess the effectiveness of a 7-day warm-water immersion (\~40°C) protocol in enhancing whole-body heat loss in older adults. Warm-water immersion will consist of a one-hour immersion in warm water with core temperature clamped at 38.5°C. Improvements in whole-body heat loss will be assessed during an incremental exercise protocol performed in dry heat (i.e., 40°C, \~15% relative humidity) prior to and following the 7-day passive heat acclimation protocol. The incremental exercise protocol will consist of three 30 minute exercise bouts performed at increasing fixed rates of metabolic heat production (i.e., 150, 200, and 250 W/m2), each separated by 15-minutes of recovery, with exception final recovery will be 1-hour in duration) performed in a direct calorimeter (a device that provides a precise measurement of the heat dissipated by the human body).


Eligibility criteria: Inclusion Criteria:

* Elderly (60-80 years), non-smoking adults.
* Not engaged in regular physical activity (\>2 sessions/week for ≥20 minutes per session).
* Willing to provide informed consent.
* Healthy, no diagnosed health conditions.
* Body Mass index (BMI) \<35 kg/m2.

Exclusion Criteria:

* Heat adapted due to repeated exposure to hot environments within the last 3 weeks (use sauna, recent travel to hot climates, other).

Primary outcomes:
measure: Evaporative heat loss
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Evaporative heat loss
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Evaporative heat loss
timeFrame: End of 30 minute bout 3 (average of last 5 minutes).
measure: Whole-body heat loss
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Whole-body heat loss
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Whole-body heat loss
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Secondary outcomes:
measure: Body heat storage
timeFrame: Change from start to end of 30 minute exercise bout 1
measure: Body heat content
timeFrame: Change from start to end of 30 minute exercise bout 2
measure: Body heat storage
timeFrame: Change from start to end of 30 minute exercise bout 3
measure: Cumulative body heat storage
timeFrame: Change from baseline resting to end of exercise bout 3
measure: Dry heat loss
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Dry heat loss
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Dry heat loss
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Core temperature
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Core temperature
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Core temperature
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Change in core temperature
timeFrame: Change from baseline resting to end of end of 30 minute exercise bout 3.
measure: Skin temperature
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Skin temperature
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Skin temperature
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Change in skin temperature
timeFrame: Change from baseline resting to end of end of 30 minute exercise bout 3.
measure: Heart rate
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Heart rate
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Heart rate
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Heart rate variability
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Heart rate variability
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Heart rate variability
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Thermal comfort scale
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Thermal comfort scale
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Thermal comfort scale
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Thermal sensation scale
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Thermal sensation scale
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Thermal sensation scale
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Thirst sensation scale
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Thirst sensation scale
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Thirst sensation scale
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
measure: Rating of perceived exertion
timeFrame: End of 30 minute exercise bout 1 (average of last 5 minutes).
measure: Rating of perceived exertion
timeFrame: End of 30 minute exercise bout 2 (average of last 5 minutes).
measure: Rating of perceived exertion
timeFrame: End of 30 minute exercise bout 3 (average of last 5 minutes).
Other outcomes:
Locations:
city: Ottawa
country: Canada
facility: Univerisity of Ottawa
state: Ontario
Study officials:
affiliation: University of Ottawa
name: Glen P Kenny, PhD.
role: PRINCIPAL_INVESTIGATOR
References: