Assess the effect of skin rewarming during lower body negative pressure upon arterial blood pressure and tolerance to simulated blood loss after exercise in the cold.
Individuals who have experienced a hemorrhagic insult are often wrapped in a warm blanket. In individuals who have exercise in a cold environment, it is unknown how this skin warming influence tolerance to simulated blood loss and whether there is an optimal temperature to warm the skin up to in order to lower blood pressure (permissive hypotension). After an initial study visit to examine exercise capacity (Visit 1), participants will complete four trials (Visits 2 through 5) After exercise in a cold environment, participants will have cold skin temperatures (\~82°F; Visit 2). Researchers will examine how increasing skin temperature to normal (\~90°F; Visit 3), warm (93°F; Visit 4) and hot (95°F; Visit 5) influences arterial blood pressure and tolerance to simulated blood loss compared to when the skin remains cold. This project will test the hypothesis that skin rewarming to \~95°F lowers arterial blood pressure without impairing tolerance to simulated blood loss (lower body negative pressure; LBNP) relative to when the skin is kept cold (82°F). Primary data include core and skin temperatures, arterial blood pressure and LBNP tolerance time. Secondary variables include skin blood flow and heart rate. After completing visit 1 first, all participants will complete visits 2 through 5 in a randomized order and participants are blinded. The order will be counterbalanced between participants.
Study Type
INTERVENTIONAL
Allocation
NA
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
10
Sixty seconds after the onset of lower body negative pressure (LBNP) skin temperature will be increased to \~90°F and held here for the duration of the LBNP test.
Sixty seconds after the onset of lower body negative pressure (LBNP) skin temperature will be increased to \~93°F and held here for the duration of the LBNP test.
Sixty seconds after the onset of lower body negative pressure (LBNP) skin temperature will be increased to \~95°F and held here for the duration of the LBNP test.
University of Colorado Colorado Springs
Colorado Springs, Colorado, United States
Arterial blood pressure
During simulated blood loss is the reduction in arterial blood pressure greater with progressive skin heating
Time frame: Before and during lower body negative pressure (LBNP) procedure
Tolerance to simulated blood loss
Tolerance to LBNP will be quantified using the cumulative stress index (CSI) calculated by summing the time at each level of LBNP multiplied by that level (i.e., 20 mmHg \* 3 min + 30 mmHg \* 3 min + 40 mmHg \* 3 min, etc.) until test termination.
Time frame: Lower body negative pressure test duration in all trials.
Core temperature
Measured using rectal probe or intestinal pill and indicative of change in internal body temperature.
Time frame: Throughout exercise cold exposure and continuously during LBNP
Cutaneous Vascular Conductance
Skin blood flow measured using laser Doppler flowmetry (AU) will be referenced relative to arterial blood pressure (mmHg) and expressed as cutaneous vascular conductance (CVC; AU/mmHg)
Time frame: Before and during lower body negative pressure (LBNP) procedure
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Sixty seconds after the onset of lower body negative pressure (LBNP) skin temperature will remain lowered to \~82°F for the duration of the LBNP test.