Fig. 1. Right subclavian vein (sv), internal jugular vein (jv), and brachiocephalic vein (bc) projected onto a three-dimensional bone computed tomography image by tracing those veins from coronal multislice computed tomography. Overlap length (  shaded black ) of the clavicle and subclavian vein passing beneath the clavicle increases with lower shoulder position. In addition, lowering the shoulder produces caudal traction of the subclavian vein, increasing tension on the vessel walls so that the junction of the brachiocephalic and jugular veins is shifted to the right. Tension on the subclavian vein increases with downward position of the shoulder. (  A ) Elevated shoulder position; (  B ) neutral shoulder position; (  C ) lowered shoulder position. 1rb = first rib; cl = clavicle.