Clinical trial NCT05847712: Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part I
Official title: Safe Maximum Work Times and the Effectiveness of Work-rest Allocations in Mitigating Increases in Core Temperature During and on the Day Following Prolonged Moderate-intensity Work in the Heat in Young and Older Workers
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: NA
Conditions: Core Temperature
Heat Stress, Exertional
Heat Fatigue
Exercise
Keywords: Heat exposure
Heat strain
Body temperature
Thermoregulation
Occupational heat stress
Uncompensable heat stress
Aging
Sex
Lead sponsor: University of Ottawa
Sponsor class: OTHER
First posted: 2023-05-08
Enrollment: 60
Sex: ALL
Minimum age (years): 18
Maximum age (years): 69
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: yes
Allocation: NON_RANDOMIZED
Intervention model: PARALLEL
Primary purpose: BASIC_SCIENCE

Brief summary: Workplaces rely on upper heat stress limits provided by the American Conference of Governmental Industrial Hygienists (ACGIH) to manage the health and safety of workers in hot environments. This is primarily achieved by interspersing work with rest periods, the length of which is dictated by environmental conditions and work intensity, to maintain core temperature at or below 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels). However, these guidelines employ a "one size fits all" approach to exposure limits that does not consider individual variation between workers. Moreover, they fail to provide direction on the safe, initial stay times before these heat-mitigation controls should be employed (i.e., rest breaks) in conditions exceeding upper heat stress limits. While recent work has generated estimates of the initial stay times for young to older men before heat-mitigation controls are required for moderate-intensity work, this information is limited to a single work bout and does not consider a second work bout preceded by an extended rest period (e.g., lunch) or next day effects. This is a key consideration, as prolonged work in the heat has been shown to cause next-day impairments in heat dissipation in older men. Further, it remains unclear if the application of the prescribed ACGIH work-rest allocations thereafter would alleviate increases in core temperature for the duration of the work period (e.g., start of shift versus post-lunch period). This project will address these knowledge gaps by determining if refinements in initial stay times for moderate-intensity work (represents the average work effort of physically demanding occupations) in the heat (26°C wet-bulb globe temperature) may be required for young and older adults for i) a second work bout that is preceded by an extended rest period such as a lunch break, and ii) a work bout performed on the next day. This includes assessing the efficacy of the prescribed ACGIH work-rest allocations to mitigate increases in core temperature beyond safe limits (\>38.0°C, equivalent to a \>1°C increase in body core temperature above resting levels) during these work periods. Given the known sex-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will conduct separate analysis to identify modulating effects of biological sex on the initial stay times and effectiveness of the work-rest allocation as a heat-alleviation control.


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 first (morning day 1) continuous work bout
measure: Initial stay time
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Initial stay time
timeFrame: End of third (morning day 2) continuous work bout
measure: Average core temperature
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Average core temperature
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 1
measure: Average core temperature
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
Secondary outcomes:
measure: Heart rate at initial stay time
timeFrame: End of first (morning day 1) continuous work bout
measure: Heart rate at initial stay time
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Heart rate at initial stay time
timeFrame: End of third (morning day 2) continuous work bout
measure: Average heart rate
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Average heart rate
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 1
measure: Average heart rate
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
measure: Skin temperature at initial stay time
timeFrame: End of first (morning day 1) continuous work bout
measure: Skin temperature at initial stay time
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Skin temperature at initial stay time
timeFrame: End of third (morning day 2) continuous work bout
measure: Average skin temperature
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Average skin temperature
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 1
measure: Average skin temperature
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
measure: Systolic blood pressure
timeFrame: End of first (morning day 1) work period
measure: Systolic blood pressure
timeFrame: End of second (afternoon day 1) work period
measure: Systolic blood pressure
timeFrame: End of third (morning day 2) work period
measure: Diastolic blood pressure
timeFrame: End of first (morning day 1) work period
measure: Diastolic blood pressure
timeFrame: End of second (afternoon day 1) work period
measure: Diastolic blood pressure
timeFrame: End of third (morning day 2) work period
measure: Mean arterial blood pressure
timeFrame: End of first (morning day 1) work period
measure: Mean arterial blood pressure
timeFrame: End of second (afternoon day 1) work period
measure: Mean arterial blood pressure
timeFrame: End of third (morning day 2) work period
measure: Rate pressure product
timeFrame: End of first (morning day 1) work period
measure: Rate pressure product
timeFrame: End of second (afternoon day 1) work period
measure: Rate pressure product
timeFrame: End of third (morning day 2) work period
measure: Fluid consumption
timeFrame: End of first (morning day 1) work period
measure: Fluid consumption
timeFrame: End of second (afternoon day 1) work period
measure: Fluid consumption
timeFrame: End of third (morning day 2) work period
measure: Fluid loss
timeFrame: End of first (morning day 1) work period
measure: Fluid loss
timeFrame: End of second (afternoon day 1) work period
measure: Fluid loss
timeFrame: End of third (morning day 2) work period
measure: Change in plasma volume
timeFrame: End of first (morning day 1) work period
measure: Change in plasma volume
timeFrame: End of second (afternoon day 1) work period
measure: Change in plasma volume
timeFrame: End of third (morning day 2) work period
measure: Thermal comfort scale
timeFrame: End of first (morning day 1) continuous work bout
measure: Thermal comfort scale
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Thermal comfort scale
timeFrame: End of third (morning day 2) continuous work bout
measure: Thermal comfort scale
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Thermal comfort scale
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 1
measure: Thermal comfort scale
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
measure: Thirst sensation scale
timeFrame: End of first (morning day 1) continuous work bout
measure: Thirst sensation scale
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Thirst sensation scale
timeFrame: End of third (morning day 2) continuous work bout
measure: Thirst sensation scale
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Thirst sensation scale
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 2
measure: Thirst sensation scale
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
measure: Rating of Perceived Exertion
timeFrame: End of first (morning day 1) continuous work bout
measure: Rating of Perceived Exertion
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Rating of Perceived Exertion
timeFrame: End of third (morning day 2) continuous work bout
measure: Rating of Perceived Exertion
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Rating of Perceived Exertion
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 2
measure: Rating of Perceived Exertion
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: End of first (morning day 1) continuous work bout
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: End of second (afternoon day 1) continuous work bout
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: End of third (morning day 2) continuous work bout
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: Period of work-rest allocations following initial stay time for morning day 1
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: Period of work-rest allocations following initial stay time for afternoon day 1
measure: Orthostatic Intolerance Symptoms Assessment
timeFrame: Period of work-rest allocations following initial stay time for morning day 2
Other outcomes:
Locations:
city: Ottawa
country: Canada
facility: University of Ottawa
state: Ontario
Study officials:
affiliation: University of Ottawa
name: Glen P Kenny, PhD
role: PRINCIPAL_INVESTIGATOR
References: