Veno-Constriction of the Basilic Vein with Systemic Sympathetic Activation in Humans

Abstract

Cardiac function is determined to a large extent by central venous volume-dependent cardiac filling pressure. Controlling the distribution of blood volume between the central and peripheral veins is therefore a key component of cardiovascular function. Reduction in peripheral venous volume via the muscle pump or vasoconstriction-induced passive venous recoil is well documented. However, in humans little is known about sympathetic venoconstriction, especially in larger conduit veins that drain the leg or arm. PURPOSE: To determine whether systemic sympathetic nervous system activation (SNA) can induce veno-constriction in human limb conduit veins. METHODS: 10 Male subjects lay supine with arms extended at heart level. Heart rate (HR) and mean arterial blood pressure (MAP) were measured using electrocardiogram (ECG) and arterial tonometry. Echo ultrasound was used to continuously measure basilic vein diameter ∼10–15 cm above the left elbow. Venous pressure was kept constant at 40 mmHg via inflation of a pressure cuff placed proximal to the site if vessel imaging. There were four experimental interventions: Physical Stress Evoked SNA (PS; maintained, vigorous lower limb isometric contraction), Mental Stress Evoked SNA (MS; STROOP word color test) Emotional Stress Evoked SNA (ES; anger interview), and a control condition (C; counting forward by one). Venous diameter was measured over 4 repeats of 2 minute baseline, 2 minute intervention, 4 minute recovery periods. The order of interventions was counter balanced. RESULTS: All data are mean VSE. All three SNA interventions resulted in significant reductions in venous diameter (mm) (baseline vs. intervention): PS – 5.91 ± 0.15 vs. 4.66 ± 0.26, P<0.05; MS – 5.85 ± 0.15 vs. 4.88 ± 0.16, P<0.05; ES – 5.90 ± 0.10 vs. 4.66 ± 0.32, P<0.05. No change was observed in the control intervention C – 5.91 ± 0.11 vs. 5.80 ± 0.12, P=NS. All three SNA interventions evoked significant increases in MAP (mmHg) (baseline vs. intervention): PS – 80.72 ± 1.81 vs. 112.50 ± 1.84, P<0.05; MS- 82.52 ± 1.86 vs. 96.12 ± 3.37, P<0.05; ES – 81.00 ± 2.49 vs. 91.71 ± 5.19, P<0.05. No change was observed in the control intervention C – 80.19 ± 2.39 vs. 83.11 ±2.90, P<0.05). CONCLUSION: Activation of systemic sympathetic nervous activity resulting in the elevation of arterial blood pressure is accompanied by constriction of the basilic conduit vein in humans. This confirms sympathetic innervation of this vein in humans and the capacity for human conduit vein volume to be regulated via sympathetic activation. Supported by: Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, Ontario Innovation Trust