Flow-Mediated Dilation of the Radial Artery Is Offset by Flow-Induced Reduction in Transmural Pressure

Flow-mediated dilation of the brachial or radial artery in response to transient hyperaemic flow, the most widely used test of endothelial function, is only manifest after flow decays back to baseline. We examined whether this dissociation of flow and diameter might be explained by a reduction in transmural pressure generated by high flow. Studies were performed in healthy subjects 20 to 55 years of age. Flow-mediated dilation was measured in the radial artery using a standard protocol and after flow interruption at peak hyperemia during brachial artery infusion of saline and the NO synthase inhibitor NG-monomethyl-L-arginine (8 mu mol/min). Flow interruption 20 seconds after cuff release (during high flow but no dilatation) produced an immediate increase in radial artery diameter of 5.36 +/- 2.12%, inhibited by NG-monomethyl-L-arginine to 1.09 +/- 0.67% (n=8; P