Clinical trial NCT06543719: Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part II
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 Heavy-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
Lead sponsor: University of Ottawa
Sponsor class: OTHER
First posted: 2024-08-09
Enrollment: 21
Sex: MALE
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 (e.g., age) 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, information on initial stay times for heavy-intensity work remains to be assessed. This project will assess the initial stay times for heavy-intensity work for a single work bout as well as for a second work bout that is preceded by an extended rest period such as a lunch break and a work bout performed on the next day to determine if refinements in initial stay times across these periods may be required. Further, the investigators will evaluate if the application of recommended 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). Given the known age-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will assess responses response in young and older adults.


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 of 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 first (afternoon day 1) continuous work bout
measure: Heart rate at initial stay time
timeFrame: End of first (morning day 2) continuous work bout
measure: Average heart rate
timeFrame: Period of work-rest allocations following initial stay time for morning of day 1
measure: Average heart rate
timeFrame: Period of work-rest allocations following initial stay time for afternoon of day 1
measure: Average heart rate
timeFrame: Period of work-rest allocations following initial stay time for morning of 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 first (afternoon day 1) continuous work bout
measure: Skin temperature at initial stay time
timeFrame: End of first (morning day 2) continuous work bout
measure: Average skin temperature
timeFrame: Period of work-rest allocations following initial stay time for morning of day 1
measure: Average skin temperature
timeFrame: Period of work-rest allocations following initial stay time for afternoon of day 1
measure: Average skin temperature
timeFrame: Period of work-rest allocations following initial stay time for morning of 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 1) work period
measure: Mean arterial pressure
timeFrame: End of first (morning day 1) work period
measure: Mean arterial pressure
timeFrame: End of second (afternoon day 1) work period
measure: Mean arterial 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 of day 1
measure: Thermal comfort scale
timeFrame: Period of work-rest allocations following initial stay time for afternoon of day 1
measure: Thermal comfort scale
timeFrame: Period of work-rest allocations following initial stay time for morning of 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 period
measure: Thirst sensation scale
timeFrame: End of third (morning day 2) continuous work period
measure: Thirst sensation scale
timeFrame: Period of work-rest allocations following initial stay time for morning of 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 of 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 of day 1
measure: Rating of Perceived Exertion
timeFrame: Period of work-rest allocations following initial stay time for afternoon of day 1
measure: Rating of Perceived Exertion
timeFrame: Period of work-rest allocations following initial stay time for morning of 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 (afternoon day 1) continuous work bout
Other outcomes:
Locations:
city: Ottawa
country: Canada
facility: University of Ottawa
state: Ontario
Study officials:
References: