In cold weather environments, blood flow to the extremities is significantly reduced, which severely impairs hand function and induces thermal discomfort. Prolonged or repeated cold exposure elicits an adaptive habituation response that is characterized by blunted skin vasoconstriction and thus may be an effective strategy to improve peripheral perfusion, reduce thermal discomfort, and maintain hand function during cold weather military operations. Since mission conditions often involve low ambient temperatures, countermeasures that reduce cold-induced decrements in hand function and thermal comfort are important to enhance Warfighter readiness in cold weather battlefield environments. The goals of this study are to 1) evaluate the effectiveness of cold habituation in improving skin blood flow, hand function, and thermal comfort during cold exposure and 2) identify the mechanisms that contribute to improvements in skin blood flow following habituation.
Participants (n=15, 18-39 yrs) will complete a preliminary cold air exposure (baseline testing) followed by 8 days of repeated cold air exposures with minimal clothing. The cold exposures will be 2 hours in duration and will be conducted in 8°C (46°F) conditions. Before and after the repeated cold exposures, participants will undergo hand function tests, assessments of thermal comfort, and skin blood flow testing.
Study Type
INTERVENTIONAL
Allocation
NA
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
16
8 consecutive days of exposure to 8°C air for 120 minutes each day
U.S. Army Research Institute of Environmental Medicine
Natick, Massachusetts, United States
Skin blood flow
Skin blood flow will be measured using non-invasive laser-Doppler flowmetry probes before and during cold exposure. Output (red blood cell flux) will be divided by mean arterial blood pressure to give an index of cutaneous vascular conductance \[CVC, flux/mmHg\].
Time frame: 8 days
Skin temperature
Skin temperatures \[in °C\] at up to 10 sites on the body will be measured using skin thermistors before and during cold exposure. Hand and foot skin temperatures will also be measured with a thermography imaging camera.
Time frame: 8 days
Manual dexterity - Pegboard
Pegboard scores will be obtained before and during cold exposure. Scores are the number of pegs placed into the boards.
Time frame: 3 days
Manual dexterity - Minnesota Rate of Manipulation
Minnesota Rate of Manipulation dexterity scores will be obtained before and during cold exposure. Scores are the time \[in seconds\] required to move small blocks various distances.
Time frame: 3 days
Hand and finger strength
Pinch and hand strength \[in kg\] will be measured using a pinch meter and grip strength device (dynamometer). Participants will complete three pinch strength tests and one grip strength test before and during cold exposure.
Time frame: 3 days
Cold perception
Ratings of thermal comfort, thermal sensation, and pain perception \[in arbitrary units\] will be assessed using visual analogue scales before and during cold exposure.
Time frame: 5 days
Metabolic heat production
Oxygen consumption and carbon dioxide production \[ml/kg/min\] will be measured using computerized indirect calorimetry before and during cold exposure. Oxygen consumption and carbon dioxide production will be combined to report metabolic heat production in Watts per meter squared.
Time frame: 5 days
Body core temperature
Body core temperature \[in °C\] will be measured using a telemetry pill self-inserted as a suppository during cold exposure.
Time frame: 5 days
Blood pressure
Brachial artery blood pressure \[in mmHg\] will be measured using an automated blood pressure cuff before and during cold exposure.
Time frame: 12 days
Plasma norepinephrine
Circulating concentrations of norepinephrine \[in pg/ml\] will be assessed in blood collected via venipuncture before and after cold exposure.
Time frame: 3 days
Heart rate
Heart rate \[in beats per min\] will be measured using an automated cuff before and during cold exposure.
Time frame: 12 days
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