Flow-mediated and reflex changes in large peripheral artery tone in humans.

Studies of peripheral blood vessels in humans have focused primarily on regulation of blood flow and vascular resistance, which are thought to reflect small vessel caliber. Recent studies in animals have identified flow-mediated and neurogenic changes in large artery diameter. This study tested for flow-mediated dilatation and reflex constriction of the brachial artery in humans. A dual-crystal pulsed Doppler system was used to measure brachial artery diameter and blood flow proximal to the antecubital fossa. To test for flow-mediated dilatation, flow through the brachial artery was altered by an occluding cuff placed on the forearm distal to the site of brachial artery flow and diameter measurement. Control blood flow was 123 +/- 20 ml/min, and brachial artery diameter was 4.74 +/- 0.17 mm (mean +/- SEM). By inflating the distal occluding cuff (distal circulatory arrest), flow was reduced through the brachial artery to 21 +/- 5 ml/min (p less than 0.005), and brachial artery diameter was reduced to 4.35 +/- 0.20 mm (p less than 0.001). By deflating the distal occluding cuff after 10 minutes (reactive hyperemia), brachial artery flow was increased to 358 +/- 55 ml/min (p less than 0.001), and diameter was increased to 5.6 +/- 0.19 mm (p less than 0.001). These interventions did not change systemic arterial pressure and, as measured in three subjects, caused only small changes in local brachial artery distending pressure. Thus, both increased and decreased brachial artery blood flow produced significant changes in brachial artery diameter without altering arterial distending pressure. These data provide evidence for flow-mediated dilatation in humans.(ABSTRACT TRUNCATED AT 250 WORDS)