Working in the Heat at Simulated Altitude: Effects of Normobaric Hypoxia on Physiological Strain
2026年7月11日 更新者：Glen P. Kenny、University of Ottawa
Effects of Normobaric Hypoxia on Initial Stay Time and Physiological Strain During Moderate-Intensity Work in the Heat in Young and Older Males
Extreme heat events are becoming more frequent, intense, and prolonged, increasing the risk of heat-related illness among workers performing physically demanding work in hot environments. Occupational heat-stress guidelines use work-rest schedules to limit increases in core temperature and physiological strain, but they do not clearly define the safe maximum duration of continuous work before heat-mitigation controls should begin, known as the initial stay time. Recent work has generated initial stay time recommendations for young and older workers performing moderate-intensity work in the heat; however, these recommendations were developed under normoxic conditions. In many workplaces, heat may occur alongside additional stressors such as hypoxia, including work at altitude or in oxygen-reduced environments. Hypoxia can increase cardiovascular strain, reduce arterial oxygen saturation, and impair exercise tolerance, potentially compromising heat-stress guidance developed under normal oxygen conditions. Older workers may be especially vulnerable because of age-related reductions in thermoregulatory and cardiovascular function. It remains unclear whether hypoxia increases physiological strain during work in the heat or whether current initial stay time and recovery recommendations remain protective under combined heat and hypoxic stress.
The primary objective of this study is to determine whether hypoxia increases physiological strain during moderate-intensity work in the heat in young and older males. Specifically, the study will assess whether normoxia-derived initial stay times and recovery recommendations for work at 29°C wet-bulb globe temperature (37.5°C, 35% RH) remain effective during exposure to 14% inspired oxygen, simulating approximately 3000 m altitude. Healthy young and older males will complete two simulated occupational heat exposures: heat alone and heat plus hypoxia. Participants will perform moderate-intensity treadmill work based on age-specific initial stay times, followed by prescribed work-rest cycles and seated recovery. Core temperature, cardiovascular strain, oxygen saturation, skin temperature, hydration status, perceptual responses, mood, environmental stress symptoms, and cognitive function will be assessed to determine whether hypoxia modifies responses to work in the heat. Findings will help determine whether occupational heat-stress guidance requires refinement for workers exposed to combined heat and hypoxic stress.
調査の概要
状態
募集
研究の種類
介入
入学 (推定)
20
段階
- 適用できない
連絡先と場所
このセクションには、調査を実施する担当者の連絡先の詳細と、この調査が実施されている場所に関する情報が記載されています。
研究連絡先
- 名前：Glen P Kenny, PhD
- 電話番号：4282 6135625800
- メール：gkenny@uottawa.ca
研究場所
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Ontario
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Ottawa、Ontario、カナダ、K1N 6N5
- 募集
- University of Ottawa
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コンタクト：
- Glen P Kenny, PhD
- 電話番号：4282 613-562-5800
- メール：gkenny@uottawa.ca
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-
参加基準
研究者は、適格基準と呼ばれる特定の説明に適合する人を探します。これらの基準のいくつかの例は、人の一般的な健康状態または以前の治療です。
適格基準
就学可能な年齢
- 大人
- 高齢者
健康ボランティアの受け入れ
いいえ
説明
Inclusion Criteria:
- Are male.
- Do not smoke or have been smoke free for at least 5 years.
- English or French speaking.
- Ability to provide informed consent.
- Are physically active (engage in exercise at least 2 times per week for ≥30 minutes)
Exclusion Criteria:
- Are regularly exposed to hot environments (e.g., occupational heat exposure)
- Are regularly exposed to hypoxic environments (e.g., high altitudes)
- Experience claustrophobia or discomfort in enclosed environments
- Episode(s) of severe hypoglycemia (requiring the assistance of another person) within the previous year, or inability to sense hypoglycemia (hypoglycemia unawareness).
- Serious complications related to diabetes (gastroparesis, renal disease, uncontrolled hypertension, severe autonomic neuropathy).
- Uncontrolled hypertension - BP >150 mmHg systolic or >95 mmHg diastolic in a sitting position.
- Restrictions in physical activity due to disease (e.g. intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.).
- Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
- Cardiac abnormalities identified during screening
研究計画
このセクションでは、研究がどのように設計され、研究が何を測定しているかなど、研究計画の詳細を提供します。
研究はどのように設計されていますか？
デザインの詳細
- 主な目的：基礎科学
- 割り当て：ランダム化
- 介入モデル：クロスオーバー割り当て
- マスキング：独身
武器と介入
参加者グループ / アーム |
介入・治療 |
|---|---|
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実験的：Normoxic exposure
Participants complete a simulated moderate-intensity occupational heat exposure protocol in a hot environment (37.5°C, 35% RH) under normoxic conditions.
Participants walk on a treadmill until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.
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Participants complete a simulated moderate-intensity occupational heat exposure protocol involving treadmill walking in a hot environment (37.5°C, 35% RH) under normoxic conditions (~20.9% inspired oxygen).
Participants walk until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.
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実験的：Hypoxic exposure
Participants complete a simulated moderate-intensity occupational heat exposure protocol in a hot environment (37.5°C, 35% RH) with an added hypoxic exposure equivalent to 14% inspired oxygen.
Participants walk on a treadmill until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.
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Participants complete a simulated moderate-intensity occupational heat exposure protocol involving treadmill walking in a hot environment (37.5°C, 35% RH) with an added hypoxic exposure equivalent to 14% inspired oxygen.
Participants walk until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.
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この研究は何を測定していますか？
主要な結果の測定
結果測定 |
メジャーの説明 |
時間枠 |
|---|---|---|
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Total work volume
時間枠：During the 240-minute work period
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Total work completed during the 240-minute work bout.
The work period consists of an initial continuous walking phase to a core temperature 38.0°C or 1°C increase above baseline resting, followed by intermittent work-rest cycles.
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During the 240-minute work period
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二次結果の測定
結果測定 |
メジャーの説明 |
時間枠 |
|---|---|---|
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Time to core temperature of 38.0°C
時間枠：During the 240-minute work period
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Time, in minutes, from the start of continuous walking to the point at which core temperature reaches 38.0°C.
Participants who do not reach 38.0°C before voluntary termination, reaching the applicable stopping criterion, or completing 240 minutes of continuous walking will have their time recorded at termination or completion.
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During the 240-minute work period
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Time to 1.0°C increase in core temperature
時間枠：During the 240-minute work period
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Time, in minutes, from the start of continuous walking to the point at which rectal temperature increases by 1.0°C above baseline.
For participant safety, continuous walking will not continue beyond a rectal temperature of 38.5°C.
Therefore, for participants who reach 38.5°C before attaining a 1.0°C increase in rectal temperature, the time at which 38.5°C is reached will be recorded.
Participants who voluntarily terminate exercise or complete 240 minutes of continuous walking before reaching either endpoint will have their time recorded at termination or completion.
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During the 240-minute work period
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Average core temperature during work/rest cycles
時間枠：During the 240-minute work period
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Average core temperature measured during the intermittent work-rest cycles following the initial continuous work period.
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During the 240-minute work period
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Heart rate at core temperature of 38.0°C
時間枠：During the 240-minute work period
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Heart rate measured at the time a participant reaches a rectal temperature of 38.0°C during the initial continuous walking period.
For participants who do not reach a rectal temperature of 38.0°C before voluntary termination, reaching the applicable stopping criterion, or completing 240 minutes of continuous walking, heart rate at termination or completion will be recorded.
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During the 240-minute work period
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Heart rate at 1.0°C increase in core temperature
時間枠：During the 240-minute work period
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Heart rate measured at the time a participant achieves a 1.0°C increase in core temperature above baseline during the initial continuous walking period.
For participant safety, continuous walking will not continue beyond a core temperature of 38.5°C.
Therefore, for participants who reach a core temperature of 38.5°C before attaining a 1.0°C increase above baseline, the heart rate at 38.5°C will be recorded.
Participants who voluntarily terminate exercise or complete 240 minutes of continuous walking before reaching either endpoint will have their final recorded heart rate used.
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During the 240-minute work period
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Average heart rate during work/rest cycles
時間枠：During the 240-minute work period
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Average heart rate measured during the intermittent work-rest cycles following the initial continuous work period.
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During the 240-minute work period
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Mean skin temperature at core temperature of 38.0°C
時間枠：During the 240-minute work period
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Mean skin temperature measured at the time a participant reaches a core temperature of 38.0°C during the initial continuous walking period.
For participants who do not reach a core temperature of 38.0°C before voluntary termination, reaching the applicable stopping criterion, or completing 240 minutes of continuous walking, mean skin temperature at termination or completion will be recorded.
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During the 240-minute work period
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Mean skin temperature at 1.0°C increase in core temperature
時間枠：During the 240-minute work period
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Mean skin temperature measured at the time a participant achieves a 1.0°C increase in core temperature above baseline during the initial continuous walking period.
For participant safety, continuous walking will not continue beyond a core temperature of 38.5°C.
Therefore, for participants who reach a core temperature of 38.5°C before attaining a 1.0°C increase above baseline, the mean skin temperature at 38.5°C will be recorded.
Participants who voluntarily terminate exercise or complete 240 minutes of continuous walking before reaching either endpoint will have their final recorded mean skin temperature used.
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During the 240-minute work period
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Average mean skin temperature during work/rest cycles
時間枠：During the 240-minute work period
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Average mean skin temperature measured during the intermittent work-rest cycles following the initial continuous work period.
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During the 240-minute work period
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Recovery core temperature
時間枠：During 1 hour recovery following the 240-minute work period
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Average core temperature during the recovery period.
Core temperature will be measured continuously throughout recovery.
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During 1 hour recovery following the 240-minute work period
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Recovery heart rate
時間枠：During 1 hour recovery following the 240-minute work period
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Average heart rate during the recovery period.
Heart rate will be measured continuously throughout recovery.
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During 1 hour recovery following the 240-minute work period
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Recovery mean skin temperature
時間枠：During 1 hour recovery following the 240-minute work period
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Average mean skin temperature during the recovery period.
Skin temperature will be measured continuously throughout recovery.
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During 1 hour recovery following the 240-minute work period
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Tissue oxygenation
時間枠：During 240-minute work bout and subsequent 1 hour recovery
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Functional near-infrared spectroscopy will be used to continuously assess changes in cerebral and skeletal muscle oxygenation
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During 240-minute work bout and subsequent 1 hour recovery
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Peripheral oxygen saturation
時間枠：During 240-minute work bout and subsequent 1 hour recovery
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Peripheral oxygen saturation will be continuously monitored using pulse oximetry to assess the level of arterial oxygen saturation during work and recovery; indicates the degree of hypoxemia and helps determine whether reduced oxygen availability contributes to physiological strain during heat exposure
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During 240-minute work bout and subsequent 1 hour recovery
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Urine specific gravity
時間枠：Assessed at baseline and after recovery
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Urine specific gravity will be measured to assess hydration status.
Higher values indicate greater urine concentration and therefore poorer hydration status, whereas lower values indicate lower urine concentration and therefore better hydration status.
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Assessed at baseline and after recovery
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Fluid loss from body mass change
時間枠：Assessed at baseline and throughout protocol
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Fluid loss calculated from changes in body mass during exposure, corrected for fluid intake.
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Assessed at baseline and throughout protocol
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Changes in plasma volume
時間枠：Assessed at baseline and after recovery
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Change in plasma volume from baseline values calculated from duplicate measurements of hemoglobin and hematocrit at the start and end of exposure using the technique by Dill and Costill
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Assessed at baseline and after recovery
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Systolic blood pressure
時間枠：Assessed at baseline and throughout protocol
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Systolic blood pressure measured in triplicate using automated oscillometry.
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Assessed at baseline and throughout protocol
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Diastolic blood pressure
時間枠：Assessed at baseline and throughout protocol
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Diastolic blood pressure measured in triplicate using automated oscillometry.
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Assessed at baseline and throughout protocol
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Orthostatic hypotension questionnaire
時間枠：Assessed at baseline and throughout protocol
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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"
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Assessed at baseline and throughout protocol
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Lake Louise Mountain Sickness Questionnaire
時間枠：Assessed at baseline and throughout protocol
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Assess symptoms of acute mountain sickness, including headache, gastrointestinal discomfort, fatigue/weakness, dizziness/lightheadedness, and sleep disturbance.
Each symptom is scored from 0 - 3 and summed for a total score, with higher scores indicating greater symptom severity and acute mountain sickness typically defined as headache plus a total score ≥3.
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Assessed at baseline and throughout protocol
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Thermal sensation scale
時間枠：Assessed at baseline and throughout protocol
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Thermal sensation will be assessed using a visual analog ASHRAE-based scale in response to the question "How hot do you feel?" Scores range from 0 (neutral) to 7 (extremely hot).
Higher scores indicate a greater sensation of heat and therefore a worse outcome, whereas lower scores indicate less perceived heat and therefore a better outcome.
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Assessed at baseline and throughout protocol
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Thermal comfort
時間枠：Assessed at baseline and throughout protocol
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Thermal comfort will be assessed in response to the question "How comfortable does your body temperature feel?" using a visual analog scale ranging from 1 (comfortable) to 4 (very uncomfortable).
Higher scores indicate lower thermal comfort and therefore a worse outcome, whereas lower scores indicate greater thermal comfort and therefore a better outcome.
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Assessed at baseline and throughout protocol
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Thirst sensation
時間枠：Assessed at baseline and throughout protocol
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Thirst sensation will be assessed in response to the question "How thirsty are you?" using a visual analog scale ranging from 1 (not thirsty at all) to 9 (very, very thirsty).
Higher scores indicate greater thirst and therefore a worse outcome, whereas lower scores indicate less thirst and therefore a better outcome.
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Assessed at baseline and throughout protocol
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Rating of Perceived Exertion (Borg 6-20 Scale)
時間枠：Assessed during 240-minute work period
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Perceived exertion will be assessed using a visual analog scale in response to the question "How hard are you working?" Scores range from 6 (no exertion at all) to 20 (maximal exertion).
Higher scores indicate greater perceived effort and therefore a worse outcome, whereas lower scores indicate less perceived effort and therefore a better outcome.
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Assessed during 240-minute work period
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Feel-good scale
時間枠：Assessed at baseline and throughout protocol
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Feelings of well-being will be assessed using a visual analog scale in response to the question "How good do you feel?" Scores range from -5 (very bad) to +5 (very good), with 0 representing neutral.
Higher scores indicate more positive feelings and therefore a better outcome, whereas lower scores indicate more negative feelings and therefore a worse outcome.
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Assessed at baseline and throughout protocol
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Profiles of Mood States (POMS-40) total mood disturbance score
時間枠：Assessed at baseline and end of recovery
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Mood state will be assessed using the 40-item Profiles of Mood States (POMS-40) questionnaire.
Participants will rate how they feel at the time of assessment using a 5-point Likert scale ranging from 0 (not at all) to 4 (extremely).
Responses will be summed to generate a total score.
Higher scores indicate greater overall mood disturbance and therefore a worse outcome, whereas lower scores indicate lower mood disturbance and therefore a better outcome.
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Assessed at baseline and end of recovery
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Environmental Symptoms Questionnaire-IV (ESQ-IV) total symptom score
時間枠：Assessed at baseline and end of recovery
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Environmental symptomatology associated with prolonged heat exposure will be assessed using the Environmental Symptoms Questionnaire-IV (ESQ-IV).
Participants will rate 68 symptoms using a 6-point Likert scale ranging from 0 (not at all) to 5 (extreme).
Responses are summed, with positive items reverse scored as appropriate, to generate a Total Symptom Score ranging from 0 to 340.
Higher scores indicate greater symptom burden and therefore a worse outcome, whereas lower scores indicate fewer symptoms and therefore a better outcome.
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Assessed at baseline and end of recovery
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Heart rate variability: standard deviation of normal R-R intervals (SDNN)
時間枠：During 240-minute work bout and subsequent 1 hour recovery
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Cardiac autonomic modulation will be assessed using a 5-lead Holter electrocardiogram (ECG) monitor (DigiTrak XT, Philips Zymed, Andover, MA, USA).
Consecutive R-R intervals will be derived from the ECG recording to calculate the standard deviation of normal R-R intervals (SDNN), measured in milliseconds (ms).
Higher values indicate greater heart rate variability and cardiac autonomic modulation, whereas lower values indicate reduced heart rate variability and cardiac autonomic modulation.
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During 240-minute work bout and subsequent 1 hour recovery
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Heart rate variability: root mean square of successive differences (RMSSD)
時間枠：During 240-minute work bout and subsequent 1 hour recovery
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Cardiac autonomic modulation will be assessed using a 5-lead Holter electrocardiogram (ECG) monitor (DigiTrak XT, Philips Zymed, Andover, MA, USA).
Consecutive R-R intervals will be derived from the ECG recording to calculate the root mean square of successive differences between adjacent normal R-R intervals (RMSSD), measured in milliseconds (ms).
Higher values indicate greater parasympathetic modulation and heart rate variability, whereas lower values indicate reduced parasympathetic modulation and heart rate variability.
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During 240-minute work bout and subsequent 1 hour recovery
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協力者と研究者
ここでは、この調査に関係する人々や組織を見つけることができます。
スポンサー
捜査官
- 主任研究者：Glen P Kenny, PhD、University of Ottawa
研究記録日
これらの日付は、ClinicalTrials.gov への研究記録と要約結果の提出の進捗状況を追跡します。研究記録と報告された結果は、国立医学図書館 (NLM) によって審査され、公開 Web サイトに掲載される前に、特定の品質管理基準を満たしていることが確認されます。
主要日程の研究
研究開始 (推定)
2026年6月17日
一次修了 (推定)
2026年12月31日
研究の完了 (推定)
2027年2月28日
試験登録日
最初に提出
2026年6月17日
QC基準を満たした最初の提出物
2026年6月17日
最初の投稿 (実際)
2026年6月24日
学習記録の更新
投稿された最後の更新 (実際)
2026年7月14日
QC基準を満たした最後の更新が送信されました
2026年7月11日
最終確認日
2026年7月1日
詳しくは
この情報は、Web サイト clinicaltrials.gov から変更なしで直接取得したものです。研究の詳細を変更、削除、または更新するリクエストがある場合は、register@clinicaltrials.gov。 までご連絡ください。 clinicaltrials.gov に変更が加えられるとすぐに、ウェブサイトでも自動的に更新されます。