Clinical trial NCT06630832: Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part III
Official title: Impact of Partial and Full Cooling Applied During Prescribed Rest Breaks to Mitigate Increases in Physiological Strain During Prolonged Work in Hot Environments.
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Body Temperature Changes
Heat Stress
Heat Exposure
Heat Fatigue
Work Related Stress
Hyperthermia
Keywords: Heat strain
Thermoregulation
Exercise
Core temperature
Occupational heat stress
Uncompensable heat stress
Aging
Lead sponsor: University of Ottawa
Sponsor class: OTHER
First posted: 2024-10-08
Enrollment: 23
Sex: MALE
Minimum age (years): 18
Maximum age (years): 69
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: yes
Allocation: RANDOMIZED
Intervention model: PARALLEL
Primary purpose: BASIC_SCIENCE

Brief summary: Occupational heat stress directly threatens workers' ability to live healthy and productive lives. Heat exposed workers are at an elevated risk of experiencing impaired work performance and cognitive function leading to a greater risk of work-related injuries which includes traumatic injury and a myriad of pathophysiological conditions (e.g., heat stroke, acute kidney injury, adverse cardiovascular events). To mitigate the adverse health effects of occupational heat stress, safety organizations recommend upper limits for heat stress, typically defined by a worker's metabolic rate and the prevailing wet-bulb globe temperature (WBGT). In instances where the heat load created by the combination of work intensity, environment, and clothing worn exceed the upper heat stress limits (uncompensable heat stress), controls such as rest breaks are prescribed to limit increases in core temperature beyond recommended limits. While workers are encouraged to find shelter from the heat during a rest break, it is not always possible or feasible. Typically, workers may rest while remaining exposed to the heat, recover in a shaded area or rest in an air-conditioned room or vehicle. However, the effectiveness of these cooling strategies in mitigating the level of physiological strain experienced by the worker during prolonged work in a hot environment remains unclear. In this project, the investigators will assess the efficacy of the different cooling strategies in preventing excursions in core temperature beyond recommended limits (38.0°C) following the initial stay time for moderate-intensity work in hot ambient conditions (WBGT of 29°C; represents hot outdoor conditions experienced by workers in summers in Ontario, Canada) in context of the prescribed American Conference of Governmental Industrial Hygienists (ACGIH) work-to-rest allocation for unacclimated adults. On three separate days, participants will walk on a treadmill at a fixed metabolic rate of 200 W/m2 until core temperature reaches and/or exceeds 38.0°C or until volitional fatigue. Thereafter, participants will complete an additional 180 min work bout employing the recommended ACGIH work-to-rest allocation of 1:3 (starting with a 45 min rest break followed by a 15 min work bout, with the cycle repeated three times over the 180 min work simulation bout) without (Control) or with cooling mitigation during each 15-min break consisting of either: i) partial cooling equivalent to sitting in a shaded space (WBGT 24°C; 31.7°C and 35% RH) such as under a tree with a light breeze (simulated with pedestal fan fixed at \~2 m/s) or ii) full cooling equivalent to sitting in air-conditioned space (e.g., room or vehicle) maintained at 22°C and 35% RH (equivalent WBGT of 16°C).


Eligibility criteria: Inclusion Criteria:

* young (18-30 years) and older adults (50-69 years)
* habitually active, not endurance trained (\<2 sessions per week, \<150 minutes per week)
* non-smoking
* English or French speaking
* ability to provide informed consent

Exclusion Criteria:

* pre-existing health conditions (e.g., diabetes, hypertension)
* use of medication deemed to significantly modulate thermoregulatory function and heat tolerance (e.g., antidepressants, antihistamines, diuretics)
* engaged in jobs and/or activities that involve frequent exposure to hot environments (e.g., regular sauna use)

Primary outcomes:
measure: Initial stay time
timeFrame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
measure: Average core temperature during work-rest allocations
timeFrame: Period of work-rest allocations over a 180 minute following the initial stay time
measure: Heart rate at initial stay time
timeFrame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
measure: Average heart rate during work-rest allocations
timeFrame: Period of work-rest allocations over a 180 minute following the initial stay time
measure: Skin temperature at initial stay time
timeFrame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
measure: Average skin temperature during work-rest allocations
timeFrame: Period of work-rest allocations over a 180 minute following the initial stay time
measure: Thermal comfort scale at initial stay time
timeFrame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
measure: Thermal comfort scale during work-rest allocations
timeFrame: Period of work-rest allocations over a 180 minute following the initial stay time
measure: Thirst sensation scale at initial stay time
timeFrame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
measure: Thirst sensation scale during work-rest allocations
timeFrame: Period of work-rest allocations over a 180 minute following the initial stay time
measure: Rating of Perceived Exertion at initial stay time
timeFrame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
measure: Rating of Perceived Exertion during work-rest allocations
timeFrame: Period of work-rest allocations over a 180 minute following the initial stay time
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: At the end of the 180 minute work-rest allocations
Secondary outcomes:
Other outcomes:
Locations:
city: Ottawa
country: Canada
facility: University of Ottawa
state: Ontario
Study officials:
References: