Hot Water Immersion as a Heat Acclimation Strategy in Older Adults

Short-term Warm Water Immersion as a Heat Acclimation Strategy to Enhance Heat Dissipation in Older Adults: An Exploratory Study

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).

Study Overview

• Status: Completed
• Conditions: Hyperthermia; Aging; Heat Stress; Thermoregulation; Heat Exposure
• Intervention / Treatment: Other: Heat acclimation

• Study Type: Interventional
• Enrollment (Actual): 12
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Canada
  • Ontario
    • Ottawa, Ontario, Canada, K1N6N5
      • Univerisity of Ottawa

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

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).

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Experimental: Heat Acclimation; Participants will undergo an exercise heat stress test prior to and following seven consecutive days of warm-water immersion (~40°C) of 1-hour duration with core temperature clamped at 38.5°C. During the exercise-heat stress test participants will perform three, successive 30-minute bouts of semi-recumbent cycling performed at increasing fixed loads of metabolic heat production of 150, 200 and 250 W/m2 (i.e., exercise bout 1, exercise bout 2 and exercise bout 3, respectively), each separated by 15-minute of rest break with the final recovery extended to 1-hour.

Other: Heat acclimation; Participants will complete a 7-day passive heat acclimation protocol consisting of immersion in warm water (~40°C) for 1 hour over 7 consecutive days.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Evaporative heat loss	Evaporative heat loss as assessed using a direct air calorimeter.	End of 30 minute exercise bout 1 (average of last 5 minutes).
Evaporative heat loss	Evaporative heat loss as assessed using a direct air calorimeter.	End of 30 minute exercise bout 2 (average of last 5 minutes).
Evaporative heat loss	Evaporative heat loss as assessed using a direct air calorimeter.	End of 30 minute bout 3 (average of last 5 minutes).
Whole-body heat loss	The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).	End of 30 minute exercise bout 1 (average of last 5 minutes).
Whole-body heat loss	The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).	End of 30 minute exercise bout 2 (average of last 5 minutes).
Whole-body heat loss	The sum of evaporative and dry heat exchange will be quantified during each exercise period (i.e., 150, 200 and 250 W/m2).	End of 30 minute exercise bout 3 (average of last 5 minutes).

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Body heat storage	Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.	Change from start to end of 30 minute exercise bout 1
Body heat content	Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.	Change from start to end of 30 minute exercise bout 2
Body heat storage	Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.	Change from start to end of 30 minute exercise bout 3
Cumulative body heat storage	Cumulative amount of heat stored within the body calculated as the temporal summation of metabolic heat production and net heat loss.	Change from baseline resting to end of exercise bout 3
Dry heat loss	Dry heat loss as assessed using a direct air calorimeter.	End of 30 minute exercise bout 1 (average of last 5 minutes).
Dry heat loss	Dry heat loss as assessed using a direct air calorimeter.	End of 30 minute exercise bout 2 (average of last 5 minutes).
Dry heat loss	Dry heat loss as assessed using a direct air calorimeter.	End of 30 minute exercise bout 3 (average of last 5 minutes).
Core temperature	Core temperature indexed by rectal/visceral temperature	End of 30 minute exercise bout 1 (average of last 5 minutes).
Core temperature	Core temperature indexed by rectal/visceral temperature	End of 30 minute exercise bout 2 (average of last 5 minutes).
Core temperature	Core temperature indexed by rectal/visceral temperature	End of 30 minute exercise bout 3 (average of last 5 minutes).
Change in core temperature	Core temperature indexed by rectal/visceral temperature	Change from baseline resting to end of end of 30 minute exercise bout 3.
Skin temperature	Skin temperature measured at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - upper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%.	End of 30 minute exercise bout 1 (average of last 5 minutes).
Skin temperature	Skin temperature measured at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - upper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%.	End of 30 minute exercise bout 2 (average of last 5 minutes).
Skin temperature	Skin temperature measured at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - upper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%.	End of 30 minute exercise bout 3 (average of last 5 minutes).
Change in skin temperature	Skin temperature measured at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - upper arm, 30%; chest, 30%; thigh, 20%; and calf, 20%.	Change from baseline resting to end of end of 30 minute exercise bout 3.
Heart rate	Measured continuously with chest-band device	End of 30 minute exercise bout 1 (average of last 5 minutes).
Heart rate	Measured continuously with chest-band device	End of 30 minute exercise bout 2 (average of last 5 minutes).
Heart rate	Measured continuously with chest-band device	End of 30 minute exercise bout 3 (average of last 5 minutes).
Heart rate variability	Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains	End of 30 minute exercise bout 1 (average of last 5 minutes).
Heart rate variability	Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains	End of 30 minute exercise bout 2 (average of last 5 minutes).
Heart rate variability	Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains	End of 30 minute exercise bout 3 (average of last 5 minutes).
Thermal comfort scale	Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")	End of 30 minute exercise bout 1 (average of last 5 minutes).
Thermal comfort scale	Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")	End of 30 minute exercise bout 2 (average of last 5 minutes).
Thermal comfort scale	Thermal comfort assessed via a questionnaire using the ASHRAE 4-point scale ("1=comfortable to 4=very uncomfortable")	End of 30 minute exercise bout 3 (average of last 5 minutes).
Thermal sensation scale	Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")	End of 30 minute exercise bout 1 (average of last 5 minutes).
Thermal sensation scale	Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")	End of 30 minute exercise bout 2 (average of last 5 minutes).
Thermal sensation scale	Thermal sensation will be assessed using the ASHRAE 7-point scale ("0=neutral to 7=extremely hot")	End of 30 minute exercise bout 3 (average of last 5 minutes).
Thirst sensation scale	Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")	End of 30 minute exercise bout 1 (average of last 5 minutes).
Thirst sensation scale	Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")	End of 30 minute exercise bout 2 (average of last 5 minutes).
Thirst sensation scale	Thirst sensation will be quantified using a 9-point scale ("1=not thirsty at all to 9=very, very thirsty")	End of 30 minute exercise bout 3 (average of last 5 minutes).
Rating of perceived exertion	Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")	End of 30 minute exercise bout 1 (average of last 5 minutes).
Rating of perceived exertion	Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")	End of 30 minute exercise bout 2 (average of last 5 minutes).
Rating of perceived exertion	Rating of perceived exertion will be quantified using a 14-point scale ("6=no exertion at all to 20=maximal exertion")	End of 30 minute exercise bout 3 (average of last 5 minutes).

Collaborators and Investigators

• Sponsor: University of Ottawa
• Investigators: Principal Investigator: Glen P Kenny, PhD., University of Ottawa

Study record dates

Study Major Dates

• Study Start (Actual): April 29, 2022
• Primary Completion (Actual): February 16, 2023
• Study Completion (Actual): February 16, 2023

Study Registration Dates

• First Submitted: April 19, 2023
• First Submitted That Met QC Criteria: April 29, 2023
• First Posted (Actual): May 1, 2023

Study Record Updates

• Last Update Posted (Actual): July 11, 2024
• Last Update Submitted That Met QC Criteria: July 9, 2024
• Last Verified: July 1, 2024

More Information

Terms related to this study

• Keywords: Aging; Thermoregulation; Heat acclimation; Warm-water immersion
• Additional Relevant MeSH Terms: Wounds and Injuries; Body Temperature Changes; Heat Stress Disorders; Hyperthermia
• Other Study ID Numbers: HEPRU-2023-02

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Deidentified participant data will be made available with approved analysis plan and signed access agreement
• IPD Sharing Time Frame: Following publication of the main study report(s)
• IPD Sharing Access Criteria: Approved analysis plan and signed access agreement
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP; ANALYTIC_CODE

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No