Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress

Sponsor

University of Ottawa (Other)

Overall Status

Not yet recruiting

CT.gov ID

NCT05847712

Collaborator

(none)

Enrollment

Location

Arms

Anticipated Duration (Months)

Patients Per Site Per Month

Study Details

Study Description

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. 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) 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.

Condition or Disease	Intervention/Treatment	Phase
Core Temperature Heat Stress, Exertional Heat Fatigue Exercise	Other: Simulated work in the heat	N/A

Study Design

Study Type:

Interventional

Anticipated Enrollment :

40 participants

Allocation:

Non-Randomized

Intervention Model:

Parallel Assignment

Masking:

Single (Outcomes Assessor)

Masking Description:

Data will be blinded prior to analysis

Primary Purpose:

Basic Science

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 Work in the Heat in Young and Older Workers

Anticipated Study Start Date :

May 1, 2023

Anticipated Primary Completion Date :

Oct 1, 2023

Anticipated Study Completion Date :

Mar 1, 2024

Arms and Interventions

Arm	Intervention/Treatment
Experimental: Younger adults Adults aged 18-30 years with no pre-existing health conditions	Other: Simulated work in the heat Participants perform a continuous moderate-intensity work bout (metabolic rate of ~200 W/m2) until core temperature reaches 38.0°C, which is immediately followed by intermittent work using a 3:1 work-rest allocation, starting with a 15 min rest break followed by a 45 min work bout for a total work duration of ~240 min. The work protocol is performed in the morning of day 1, and repeated in a post-lunch work period (i.e., afternoon of day 1) and on the morning of the next day (i.e., morning of day 2).
Experimental: Older adults Adults aged 50-69 with no pre-existing health conditions	Other: Simulated work in the heat Participants perform a continuous moderate-intensity work bout (metabolic rate of ~200 W/m2) until core temperature reaches 38.0°C, which is immediately followed by intermittent work using a 3:1 work-rest allocation, starting with a 15 min rest break followed by a 45 min work bout for a total work duration of ~240 min. The work protocol is performed in the morning of day 1, and repeated in a post-lunch work period (i.e., afternoon of day 1) and on the morning of the next day (i.e., morning of day 2).

Arm

Intervention/Treatment

Experimental: Younger adults

Adults aged 18-30 years with no pre-existing health conditions

Other: Simulated work in the heat

Participants perform a continuous moderate-intensity work bout (metabolic rate of ~200 W/m2) until core temperature reaches 38.0°C, which is immediately followed by intermittent work using a 3:1 work-rest allocation, starting with a 15 min rest break followed by a 45 min work bout for a total work duration of ~240 min. The work protocol is performed in the morning of day 1, and repeated in a post-lunch work period (i.e., afternoon of day 1) and on the morning of the next day (i.e., morning of day 2).

Experimental: Older adults

Adults aged 50-69 with no pre-existing health conditions

Other: Simulated work in the heat

Outcome Measures

Primary Outcome Measures

Initial stay time [End of first (morning day 1) continuous work bout]
Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C is achieved or the absolute core temperature is <38°C, the time of termination or end of the work bout will be taken as the initial stay time respectively).
Initial stay time [End of second (afternoon day 1) continuous work bout]
Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C is achieved or the absolute core temperature is <38°C, the time of termination or end of the work bout will be taken as the initial stay time respectively).
Initial stay time [End of third (morning day 2) continuous work bout]
Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C is achieved or the absolute core temperature is <38°C, the time of termination or end of the work bout will be taken as the initial stay time respectively).
Average core temperature [Final 2-hours of the first (morning day 1) work period]
Average core temperature over final 2-hours of each work bout
Average core temperature [Final 2-hours of the second (afternoon day 1) work period]
Average core temperature over final 2-hours of each work bout
Average core temperature [Final 2-hours of the third (morning day 2) work period]
Average core temperature over final 2-hours of each work bout

Secondary Outcome Measures

Heart rate at initial stay time [End of first (morning day 1) continuous work bout]
Heart rate at the initial increase in absolute core temperature of 38°C
Heart rate at initial stay time [End of second (afternoon day 1) continuous work bout]
Heart rate at the initial increase in absolute core temperature of 38°C
Heart rate at initial stay time [End of third (morning day 2) continuous work bout]
Heart rate at the initial increase in absolute core temperature of 38°C
Average heart rate [Final 2-hours of the first (morning day 1) work period]
Average heart rate over final 2-hours of each work bout
Average heart rate [Final 2-hours of the second (afternoon day 1) work period]
Average heart rate over final 2-hours of each work bout
Average heart rate [Final 2-hours of the third (morning day 2) work period]
Average heart rate over final 2-hours of each work bout
Skin temperature at initial stay time [End of first (morning day 1) continuous work bout]
Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C
Skin temperature at initial stay time [End of second (afternoon day 1) continuous work bout]
Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C
Skin temperature at initial stay time [End of third (morning day 2) continuous work bout]
Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C
Average skin temperature [Final 2-hours of the first (morning day 1) work period]
Average skin temperature over final 2-hours of each work bout
Average skin temperature [Final 2-hours of the second (afternoon day 1) work period]
Average skin temperature over final 2-hours of each work bout
Average skin temperature [Final 2-hours of the third (morning day 2) work period]
Average skin temperature over final 2-hours of each work bout
Systolic blood pressure [End of first (morning day 1) work period]
Arterial blood pressure measured via automated oscillometry
Systolic blood pressure [End of second (afternoon day 1) work period]
Arterial blood pressure measured via automated oscillometry
Systolic blood pressure [End of third (morning day 2) work period]
Arterial blood pressure measured via automated oscillometry
Diastolic blood pressure [End of first (morning day 1) work period]
Arterial blood pressure measured via automated oscillometry
Diastolic blood pressure [End of second (afternoon day 1) work period]
Arterial blood pressure measured via automated oscillometry
Diastolic blood pressure [End of third (morning day 2) work period]
Arterial blood pressure measured via automated oscillometry
Mean arterial blood pressure [End of first (morning day 1) work period]
Calculated as 1/3 * systolic blood pressure + 2/3 * diastolic blood pressure
Mean arterial blood pressure [End of second (afternoon day 1) work period]
Calculated as 1/3 * systolic blood pressure + 2/3 * diastolic blood pressure
Mean arterial blood pressure [End of third (morning day 2) work period]
Calculated as 1/3 * systolic blood pressure + 2/3 * diastolic blood pressure
Rate pressure product [End of first (morning day 1) work period]
Calculated as systolic blood pressure * heart rate
Rate pressure product [End of second (afternoon day 1) work period]
Calculated as systolic blood pressure * heart rate
Rate pressure product [End of third (morning day 2) work period]
Calculated as systolic blood pressure * heart rate
Fluid consumption [End of first (morning day 1) work period]
Cumulative fluid consumption calculated by weighing the participant's water intake
Fluid consumption [End of second (afternoon day 1) work period]
Cumulative fluid consumption calculated by weighing the participant's water intake
Fluid consumption [End of third (morning day 2) work period]
Cumulative fluid consumption calculated by weighing the participant's water intake
Fluid loss [End of first (morning day 1) work period]
Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).
Fluid loss [End of second (afternoon day 1) work period]
Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).
Fluid loss [End of third (morning day 2) work period]
Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).
Change in plasma volume [End of first (morning day 1) work period]
Determined from venous blood samples
Change in plasma volume [End of second (afternoon day 1) work period]
Determined from venous blood samples
Change in plasma volume [End of third (morning day 2) work period]
Determined from venous blood samples
Thermal comfort scale [End of first (morning day 1) continuous work bout]
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Thermal comfort scale [End of second (afternoon day 1) continuous work bout]
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Thermal comfort scale [End of third (morning day 2) continuous work bout]
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Thermal comfort scale [End of first (morning day 1) work period]
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Thermal comfort scale [End of second (afternoon day 1) work period]
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Thermal comfort scale [End of third (morning day 2) work period]
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Thirst sensation scale [End of first (morning day 1) continuous work bout]
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Thirst sensation scale [End of second (afternoon day 1) continuous work bout]
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Thirst sensation scale [End of third (morning day 2) continuous work bout]
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Thirst sensation scale [End of first (morning day 1) work period]
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Thirst sensation scale [End of second (afternoon day 1) work period]
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Thirst sensation scale [End of third (morning day 2) work period]
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Rating of Perceived Exertion [End of first (morning day 1) continuous work bout]
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Rating of Perceived Exertion [End of second (afternoon day 1) continuous work bout]
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Rating of Perceived Exertion [End of third (morning day 2) continuous work bout]
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Rating of Perceived Exertion [Final minute of exercise for the end of the first (morning day 1) work period]
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Rating of Perceived Exertion [Final minute of exercise for the end of the second (afternoon day 1) work period]
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Rating of Perceived Exertion [Final minute of exercise for the end of the first (morning day 2) work period]
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Orthostatic Intolerance Symptoms Assessment [End of first (morning day 1) continuous work bout]
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".
Orthostatic Intolerance Symptoms Assessment [End of second (afternoon day 1) continuous work bout]
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".
Orthostatic Intolerance Symptoms Assessment [End of third (morning day 2) continuous work bout]
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".
Orthostatic Intolerance Symptoms Assessment [End of first (morning day 1) work period]
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".
Orthostatic Intolerance Symptoms Assessment [End of second (afternoon day 1) work period]
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".
Orthostatic Intolerance Symptoms Assessment [End of third (morning day 2) work period]
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".

Eligibility Criteria

Criteria

Ages Eligible for Study:

18 Years to 69 Years

Sexes Eligible for Study:

All

Accepts Healthy Volunteers:

Yes

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)