Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part II
NCT Number: NCT06543719
Status: NOT_YET_RECRUITING
Study Type: INTERVENTIONAL
Phases: NA
Conditions: Core Temperature|Heat Stress, Exertional|Heat Fatigue|Exercise
Interventions: OTHER: Simulated work in the heat
Sponsor: University of Ottawa
Sex: MALE
Age: ADULT, OLDER_ADULT
Enrollment: 20
Study Design: Allocation: NON_RANDOMIZED|Intervention Model: PARALLEL|Masking: SINGLE (OUTCOMES_ASSESSOR)|Primary Purpose: BASIC_SCIENCE
Start Date: 2024-08-07
Completion Date: 2025-06-01
Locations: University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada

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.

Primary Outcome Measures: Initial stay time, Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (equivalent to a 1°C increase in body core temperature above resting levels) (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C (or relative increase of ≥1°C) is achieved or the absolute core temperature is \<38°C (or relative increase of \<1°C), the time of termination or end of the work bout will be taken as the initial stay time respectively)., End of first (morning day 1) continuous work bout|Initial stay time, Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (equivalent to a 1°C increase in body core temperature above resting levels) (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C (or relative increase of ≥1°C) is achieved or the absolute core temperature is \<38°C (or relative increase of \<1°C), the time of termination or end of the work bout will be taken as the initial stay time respectively)., End of second (afternoon day 1) continuous work bout|Initial stay time, Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (equivalent to a 1°C increase in body core temperature above resting levels) (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C (or relative increase of ≥1°C) is achieved or the absolute core temperature is \<38°C (or relative increase of \<1°C), the time of termination or end of the work bout will be taken as the initial stay time respectively)., End of third (morning day 2) continuous work bout|Average core temperature, Average core temperature following initial stay time, Period of work-rest allocations following initial stay time for morning day 1|Average core temperature, Average core temperature following initial stay time, Period of work-rest allocations following initial stay time for afternoon day 1|Average core temperature, Average core temperature following initial stay time, Period of work-rest allocations following initial stay time for morning of day 2
Secondary Outcome Measures: Heart rate at initial stay time, Heart rate at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C), End of first (morning day 1) continuous work bout|Heart rate at initial stay time, Heart rate at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C), End of first (afternoon day 1) continuous work bout|Heart rate at initial stay time, Heart rate at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C), End of first (morning day 2) continuous work bout|Average heart rate, Average heart rate following initial stay time, Period of work-rest allocations following initial stay time for morning of day 1|Average heart rate, Average heart rate following initial stay time, Period of work-rest allocations following initial stay time for afternoon of day 1|Average heart rate, Average heart rate following initial stay time, Period of work-rest allocations following initial stay time for morning of day 2|Skin temperature at initial stay time, Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C), End of first (morning day 1) continuous work bout|Skin temperature at initial stay time, Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C), End of first (afternoon day 1) continuous work bout|Skin temperature at initial stay time, Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C), End of first (morning day 2) continuous work bout|Average skin temperature, Average heart rate following initial stay time, Period of work-rest allocations following initial stay time for morning of day 1|Average skin temperature, Average heart rate following initial stay time, Period of work-rest allocations following initial stay time for afternoon of day 1|Average skin temperature, Average heart rate following initial stay time, Period of work-rest allocations following initial stay time for morning of day 2|Systolic blood pressure, Arterial blood pressure measured via automated oscillometry, End of first (morning day 1) work period|Systolic blood pressure, Arterial blood pressure measured via automated oscillometry, End of second (afternoon day 1) work period|Systolic blood pressure, Arterial blood pressure measured via automated oscillometry, End of third (morning day 2) work period|Diastolic blood pressure, Arterial blood pressure measured via automated oscillometry, End of first (morning day 1) work period|Diastolic blood pressure, Arterial blood pressure measured via automated oscillometry, End of second (afternoon day 1) work period|Diastolic blood pressure, Arterial blood pressure measured via automated oscillometry, End of third (morning day 1) work period|Mean arterial pressure, Calculated as 1/3 \* systolic blood pressure + 2/3 \* diastolic blood pressure, End of first (morning day 1) work period|Mean arterial pressure, Calculated as 1/3 \* systolic blood pressure + 2/3 \* diastolic blood pressure, End of second (afternoon day 1) work period|Mean arterial pressure, Calculated as 1/3 \* systolic blood pressure + 2/3 \* diastolic blood pressure, End of third (morning day 2) work period|Rate pressure product, Calculated as systolic blood pressure \* heart rate, End of first (morning day 1) work period|Rate pressure product, Calculated as systolic blood pressure \* heart rate, End of second (afternoon day 1) work period|Rate pressure product, Calculated as systolic blood pressure \* heart rate, End of third (morning day 2) work period|Fluid consumption, Cumulative fluid consumption calculated by weighing the participant's water intake, End of first (morning day 1) work period|Fluid consumption, Cumulative fluid consumption calculated by weighing the participant's water intake, End of second (afternoon day 1) work period|Fluid consumption, Cumulative fluid consumption calculated by weighing the participant's water intake, End of third (morning day 2) work period|Fluid loss, Fluid loss calculated as the change in body mass (corrected for food/fluid consumption)., End of first (morning day 1) work period|Fluid loss, Fluid loss calculated as the change in body mass (corrected for food/fluid consumption)., End of second (afternoon day 1) work period|Fluid loss, Fluid loss calculated as the change in body mass (corrected for food/fluid consumption)., End of third (morning day 2) work period|Change in plasma volume, Determined from venous blood samples, End of first (morning day 1) work period|Change in plasma volume, Determined from venous blood samples, End of second (afternoon day 1) work period|Change in plasma volume, Determined from venous blood samples, End of third (morning day 2) work period|Thermal comfort scale, Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable), End of first (morning day 1) continuous work bout|Thermal comfort scale, Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable), End of second (afternoon day 1) continuous work bout|Thermal comfort scale, Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable), End of third (morning day 2) continuous work bout|Thermal comfort scale, Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable), Period of work-rest allocations following initial stay time for morning of day 1|Thermal comfort scale, Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable), Period of work-rest allocations following initial stay time for afternoon of day 1|Thermal comfort scale, Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable), Period of work-rest allocations following initial stay time for morning of day 2|Thirst sensation scale, Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all), End of first (morning day 1) continuous work bout|Thirst sensation scale, Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all), End of second (afternoon day 1) continuous work period|Thirst sensation scale, Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all), End of third (morning day 2) continuous work period|Thirst sensation scale, Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all), Period of work-rest allocations following initial stay time for morning of day 1|Thirst sensation scale, Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all), Period of work-rest allocations following initial stay time for afternoon day 2|Thirst sensation scale, Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all), Period of work-rest allocations following initial stay time for morning of day 2|Rating of Perceived Exertion, Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)., End of first (morning day 1) continuous work bout|Rating of Perceived Exertion, Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)., End of second (afternoon day 1) continuous work bout|Rating of Perceived Exertion, Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)., End of third (morning day 2) continuous work bout|Rating of Perceived Exertion, Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)., Period of work-rest allocations following initial stay time for morning of day 1|Rating of Perceived Exertion, Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)., Period of work-rest allocations following initial stay time for afternoon of day 1|Rating of Perceived Exertion, Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)., Period of work-rest allocations following initial stay time for morning of day 2|Orthostatic Intolerance Symptoms Assessment, Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance. 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 first (morning day 1) continuous work bout|Orthostatic Intolerance Symptoms Assessment, Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance. 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 second (afternoon day 1) continuous work bout|Orthostatic Intolerance Symptoms Assessment, Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance. 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 third (afternoon day 1) continuous work bout