Physiological Strain in Young Adults During a Simulated Heat Wave

NCT06618352 | Completed

• 1 other identifier: HEPRU-2024-09-C
• Study Type: interventional
• Target: 20
• Locations: 1 country
• Sites: 1

Brief Summary

The likelihood of exposure to overheated indoor environments is increasing as climate change is exacerbating the frequency and severity of hot weather and extreme heat events. Prolonged exposure to excessive heat stress can result in a deterioration in physiological function leading to a myriad of pathophysiological conditions (e.g., heat exhaustion, acute kidney injury, adverse cardiovascular events, heat stroke) that if left untreated can lead to death. While the relationship between extreme heat events and human health has been assessed in relation to outdoor exposure to high heat conditions, relatively little is known about the effects of daylong exposures to indoor overheating on the body's physiology. In this study, investigators will examine the change in physiological responses (i.e., thermal, cardiovascular) in young (18-35 years) adults exposed to successive days and nights of high indoor temperatures typical of conditions recording in dwellings without air conditioning during the 2021 Western Heat Dome. Specifically, study participants will be housed in a large environmental chamber (outfitted with bed, work space, sitting area, kitchen and bathroom) for three successive days (three days and two nights) while exposed to indoor overheating where daytime temperatures will be maintained at 36°C (45% relative humidity; note: 36°C, temperatures experienced in homes without air-conditioning) for a 10-hour daytime exposure period (DAYTIME: defined as the time period from 9:00 to 19:00). For the nighttime exposure period (NIGHTTIME: defined as the time period from 19:00 to 9:00), participants will be exposed to nighttime temperatures fixed at 31°C (45% relative humidity; note: reductions in indoor temperatures during the nighttime in large urban centers range between 4-6°C). Participants will be permitted to move freely throughout the day in the chamber, but will be restricted from performing any physical activity except for the completion of a battery of tests (cardiovascular, cognitive and posture assessments performed prior to (as performed between 7:00 and 9:00) and the end (as performed between 17:00 and 19:00) of the daytime exposure). During the nighttime period, participants will be permitted to move freely until they decide to go to bed.

Conditions

Heat Stress; Physiological Stress

Keywords

Heat wave; Indoor temperatures; Thermoregulation; Heat strain; Young adults; Cardiovascular strain; Sleep; Fatigue

Outcome Measures

Primary Outcomes (29)

• Core temperature (Peak) during daytime

  Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the daytime period of the simulated heat wave.

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Core temperature (AUC) during daytime

  Area under the curve of rectal temperature (in degree-hours)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Core temperature end of daytime exposure

  Rectal temperature measured at hour 10 of each daytime exposure to simulated heat wave (15-min average)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Heat rate peak during daytime

  Heart rate during each daytime exposure to simulated heat wave (15-min average)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Heat rate AUC during daytime

  Heart rate measured during each daytime exposure to simulated heat wave (15-min average)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Cardiac response to standing from supine (30:15 Ratio) during daytime

  Cardiac response to standing evaluated as the ratio between the highest R-wave to R-wave interval (lowest heart rate) measured at the 30th heart beat after standing from supine (+/- 5 beats) and the lowest R-wave to R-wave interval (highest heart rate) measured at the 15th heart beat after standing (+/- 5 beats). Cardiac response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest). Assessment is perform in the morning prior to ( and following daytime exposure.

  At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Cognitive function during daytime

  Participants will be provided with a tablet device with the mobile testing platform (Sway Medical). Participants will be complete the following cognitive tests below: Reaction time: participants will be asked to initiate a movement of the device in response to a visual cue. Impulse control: participants will be asked to respond to both "go" and "no-go" visual cues. In response to the "go" cue, participants will initiate a movement of the device. Memory: participants complete both a delayed recall test and a working memory test. Executive function: participants will complete the Cued Stroop test, in which they are presented a sequence of congruent, neutral and incongruent colour-word tasks.

  At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Postural stability during daytime

  Balance will be assessed in two ways: Method 1: CDC 4-Stage Balance Test. Participants hold a tablet to their chest, then auditory cues guide participants through four consecutive stances, feet side by side, instep of one foot touching the big toe of the other foot, tandem stand with one foot in front of the other, heel touching toe, and stand on one foot. The balance assessment will be evaluated based on movement detected by an accelerometer integrated into the hardware of the tablet device (Sway Medical Inc). Method 2: Participants will be asked to stand on a BTracks force plate with their feet spread out to shoulder width, hand on their hips and eyes closed. The assessment will comprise of four trials (one practice trial) lasting 20 seconds in length and 20 seconds between trials. Center of pressure (COP) vector data along vertical (y) and horizontal (x) axes will be summed for the total path excursion length (cm) during each trial.

  At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Systolic Response to Standing From Supine during daytime

  Systolic blood pressure response to standing evaluated as the difference in blood pressure measured between the standing and supine. Standing systolic blood pressure will be taken as the lowest value of those measured after 60 and 120 seconds of standing. Systolic response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest).

  At the start (hour 0) and end of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Systolic blood pressure during daytime

  Systolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Diastolic blood pressure during daytime

  Diastolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Rate pressure product during daytime

  Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate.

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Heart rate variability: SDNN during daytime

  Standard deviation of normal-to-normal R-wave to R-wave intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Heart rate variability: RMSSD during daytime

  Root mean squared standard deviation of normal-to-normal R-wave to R-wave intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Fluid consumption during daytime

  Average hourly fluid consumption calculated by weighing participant water intake at the start and end of each hour of exposure (normalized to the exposure duration).

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Fluid loss during daytime

  Fluid loss calculated as the change in body mass during each exposure presented as a percentage of baseline body mass (corrected for food consumption)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Change in plasma volume during daytime

  Change in plasma volume from baseline values calculated from duplicate measurements of hemoglobin and hematocrit at the start and end of each exposure using the technique by Dill and Costill

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Thermal comfort scale during daytime

  Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") ranging from "extremely uncomfortable" to "extremely comfortable"(midpoint: neutral).

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Thermal sensation scale during daytime

  Thermal sensation assessed via a visual analog scale ("How hot do you feel?") ranging from "extremely hot" to "neutral"(midpoint: hot).

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Thirst sensation scale during daytime

  Thirst sensation scale assessed via a visual analog scale ("How thirsty are you?") ranging from "Very, very thirsty" to "Not thirsty at all" (midpoint: moderately thirsty).

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Arousal scale during daytime

  Felt arousal scale assessed via a visual analog scale ("How worked up are you?") ranging from "high arousal" to "low arousal".

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Orthostatic intolerance symptoms assessment during daytime

  Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance during the lying to standing tests. All symptoms scored on a scale from 0 (none) to 10 (worst possible) and include feelings of: (1) "dizziness, lightheadedness, feeling faint, or feeling like you might black out"; (2) "Problems with vision (blurring, seeing spots, tunnel vision, etc.)"; (3) "Weakness"; (4) "Fatigue"; (5) "Trouble concentrating"; and (6) "Head and neck discomfort".

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Core temperature (Peak) during nighttime

  Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the daytime period of the simulated heat wave.

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

• Core temperature (AUC) during nighttime

  Area under the curve of rectal temperature (in degree-hours)

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

• Core temperature end of nighttime

  Rectal temperature measured at hour 10 of each daytime exposure to simulated heat wave (15-min average)

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

• Heat rate peak during nighttime

  Heart rate during each daytime exposure to simulated heat wave (15-min average)

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

• Heat rate AUC during nighttime

  Heart rate measured during each daytime exposure to simulated heat wave (15-min average)

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

• Heart rate variability: SDNN during nighttime

  Standard deviation of normal-to-normal R-wave to R-wave intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

• Heart rate variability: RMSSD during nighttime

  Root mean squared standard deviation of normal-to-normal R-wave to R-wave intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).

  End of nighttime exposure (hour 24 for Day 1 and Day 2 of the three day exposure; no nighttime exposure for Day 3) (daytime defined as period between 19:00 to 9:00)

Secondary Outcomes (5)

• Muscle oxygen during battery of cardiovascular, postural and cognitive tests during daytime

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Profiles of Mood States (POMS) during daytime

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Environmental Symptoms Questionnaire (ESQ)

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Sleep quality and quantify assessment

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

• Sleepiness during daytime

  End of daytime exposure (hour 10 for Day 1, 2 and 3 of the three day exposure) (daytime defined as period between 9:00 to 19:00)

Study Arms (1)

Daylong exposure to extreme heat

EXPERIMENTAL

Young adults exposed to daylong indoor overheating associated with an extreme heat event involving a 10-hour daytime exposure at 36°C (45% relative humidity) followed by a 14-hour nighttime exposure at 31°C (45% relative humidity) over three successive days with only a daytime exposure on the final day.

Other: Simulated indoor overheating exposure

Interventions

Simulated indoor overheating exposure OTHER

Young adults exposed to a multi-day extreme heat event

Daylong exposure to extreme heat

Eligibility Criteria

• Age: 18 Years - 35 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Non-smoking.
• English or French speaking.
• Ability to provide informed consent.

You may not qualify if:

• Chronic health conditions.
• Endurance trained
• Regular exposure to heat (e.g., hot baths, sauna, regular exercise in the heat, recent vacation to area with high temperature).

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N1A2, Canada

Location

MeSH Terms

Conditions

Heat Stress Disorders; Fatigue

Condition Hierarchy (Ancestors)

Wounds and Injuries; Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Study Officials

• Glen P Kenny, PhD

  University of Ottawa

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NA
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: SINGLE GROUP
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Full Professor

Study Record Dates

• First Submitted: September 23, 2024
• First Posted: October 1, 2024
• Study Start: September 28, 2024
• Primary Completion: May 27, 2025
• Study Completion: May 27, 2025
• Last Updated: June 17, 2025

Record last verified: 2025-06

Locations

CA (1)