Sleep deprivation has long been thought to modulate thermoregulatory function. Seminal work on sleep deprivation and thermoregulation has demonstrated that sleep-deprived individuals experience greater elevations in core temperature during exercise-heat stress due to reductions in the activation of local heat loss responses of cutaneous vasodilation and sweating. However, it remains unclear 1) if reductions in local heat loss responses would compromise whole-body heat loss (evaporative + dry heat exchange) and 2) if differences exist, are they dependent on the heat load generated by exercise (increases in metabolic rate augments the rate that heat must be dissipated by the body). Further, much of the understanding of the effects of sleep deprivation on thermoregulation has been limited to assessments in young adults. Studies show that aging is associated with reduction in cutaneous vasodilation and sweating that compromise whole-body heat loss exacerbating body heat storage during moderate- and especially more vigorous-intensity exercise in the heat. However, it remains unclear if sleep deprivation may worsen this response in older adults. The purpose of this study is therefore to evaluate the effects of sleep-deprivation on whole-body total heat loss during light, moderate, and vigorous exercise-heat stress and to assess if aging may mediate this response. To achieve this objective, direct calorimetry will be employed to measure whole-body total heat loss in young (18-30 years) and older (50-65 years) men during exercise at increasing, fixed rates of metabolic heat production of 150 (light), 200 (moderate), and 250 W/m2 (vigorous) in dry heat (40°C, \~15% relative humidity) with and without 24 hours of sleep deprivation.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
21
Participants will undertake a period of 24 hours of total sleep deprivation prior to completing exercise
Participants will undertake \~8 hours of normal sleep prior to completing exercise
University of Ottawa
Ottawa, Ontario, Canada
Evaporative heat loss
Evaporative heat loss as assessed using a direct air calorimeter
Time frame: End of each exercise bout (average of last 5 minutes)
Whole-body heat loss
Net heat loss (dry plus/minus evaporative heat exchange) as assessed using a direct air calorimeter
Time frame: End of each exercise bout (average of last 5 minutes)
Dry heat loss
Total dry heat loss as assessed using a direct air calorimeter
Time frame: End of each exercise bout (average of last 5 minutes)
Body heat storage
Change in body heat storage (i.e., amount of heat stored in the body) calculated as the temporal summation of metabolic heat production and net heat loss
Time frame: Each 30 minute exercise bout and sum of all three exercise bouts
Core temperature
Rectal temperature measured as an index of core temperature
Time frame: End of each exercise bout (average of last 5 minutes)
Change in core temperature
Change in rectal temperature from baseline resting
Time frame: End of each exercise bout (average of last 5 minutes)
Heart rate
Measured continuously using a heart rate monitor
Time frame: End of each exercise bout (average of last 5 minutes)
Heart rate reserve
Percentage of the difference between the peak heart rate
Time frame: End of each exercise bout (average of last 5 minutes)
Local sweat rate (forearm, scapula)
Sweat production assessed using ventilated capsule technique
Time frame: End of each exercise bout (average of last 5 minutes)
Skin temperature
Skin temperature measured continuously at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - bicep, 30%; chest, 30%; thigh, 20%; and calf, 20%.
Time frame: End of each exercise bout (average of last 5 minutes)
Skin temperature (change)
Change in skin temperature from baseline resting as assessed at 4-sites (chest, upper arm, thigh, calf) with mean value calculated as weighted value of 4 sites - bicep, 30%; chest, 30%; thigh, 20%; and calf, 20%.
Time frame: End of each exercise bout (average of last 5 minutes)
Thermal comfort scale
Thermal comfort assessed via a self-report questionnaire upon verbal prompting (4-point scale; 1: comfortable to 4: very uncomfortable)
Time frame: End of the 30 minute resting baseline period, end of each 30 minute exercise bout, end of each 15 minute rest period, and 1 hour after final exercise period.
Thermal sensation
Thermal sensation assessed via a self-report questionnaire upon verbal prompting (7-point scale; 0: neutral to 7: extremely hot)
Time frame: End of the 30 minute resting baseline period, end of each 30 minute exercise bout, end of each 15 minute rest period, and 1 hour after final exercise period.
Thirst sensation
Thirst sensation assessed via a self-report questionnaire upon verbal prompting (9-point scale; 1: not thirsty at all to 9: very, very thirsty)
Time frame: End of the 30 minute resting baseline period, end of each 30 minute exercise bout, end of each 15 minute rest period, and 1 hour after final exercise period.
Rating of perceived exertion
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion)
Time frame: End of the 30 minute resting baseline period, end of each 30 minute exercise bout, end of each 15 minute rest period, and 1 hour after final exercise period.
Stanford sleep scale
Symptoms of tiredness assess via a self-report questionnaire upon verbal prompting (How sleepy are you?) ranging from "feeling active, vital, alert, or wide awake" to "no longer fighting sleep, sleep onset soon, having dream-like thoughts"
Time frame: End of the 30 minute resting baseline period, end of each 30 minute exercise bout, end of each 15 minute rest period, and 1 hour after final exercise period.
Variables of heart rate variability
Measures of variability computed from the time, frequency, time-frequency, scale-invariant, entropy, and other nonlinear domains (R-R interval data extracted from the electrocardiogram)
Time frame: End of each exercise (average of last 5 minutes)
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