Rachel E. Szeghy, Nina L. Stute, Stephen M. Ratchford, Abigail S.L. Stickford. Appalachian State University, Boone, NC.

Introduction: The cold pressor test (CPT) augments sympathetic outflow, causing systemic vasoconstriction. While CPT-stimulated sympathetic activity is known to impair brachial artery reactive hyperemia, less is known about its impact during passive limb movement (PLM). PLM is a lower limb microvascular function assessment often associated with local, nitric oxide (NO)-mediated vasodilation. Purpose/Methods: This study sought to measure hemodynamic responses to PLM, as assessed by Doppler ultrasound, in the seated upright position under a controlled, non-water, condition (CON) versus CPT (hand in ice water) conditions. Young healthy adults (3M/6F; 21±2yrs; 24.51±3.08kg/m2) participated in this study. The order of CON and CPT conditions was randomly assigned. In each condition, femoral artery blood velocities and diameters were continuously measured during the 60 seconds of passive leg movement (1 Hz). Total, anterograde and retrograde blood flow (BF), mean arterial pressure (MAP), and vascular conductance (VC) were calculated offline. Student’s t-tests were performed to analyze differences between conditions. Data are reported as mean ± standard deviation. Results: The total BF response to PLM, calculated as the 60 second area under the curve, was significantly reduced during CPT (171±207ml/min) compared with CON (237±193ml/min) (p=0.04). Anterograde BF during PLM tended to be lower during CPT compared with CON (CON: 293±206ml/min; CPT: 193±186ml/min; p=0.06), while retrograde BF (CON: -20±46ml/min; CPT: -22±52ml/min) during PLM was not different between conditions (p=0.93). MAP during PLM was significantly elevated during CPT compared with CON (CON: 76.73±10.86mmHg; CPT: 93.19±8.68mmHg; p=0.0001). There was a significant reduction in VC during PLM in the CPT condition compared with CON (CON: 3.14±2.26 m/min/mmHg; CPT: 1.87±2.52 m/min/mmHg; p=0.004). Conclusion: Initial results suggest a sympathoexcitatory stimulus (CPT) impairs the hyperemic response to PLM. The microvascular assessment of lower limb, NO-mediated vasodilation may be influenced by varying levels of sympathetic tone and should be considered when measuring lower limb vascular function in a variety of diseased populations.

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