Resting microvascular resistance and conduit artery tone: relevance to endothelium-dependent flow-mediated dilation

BACKGROUND: Conduit arteries respond to increases in flow by dilating, which is mediated by endothelium-derived nitric oxide. The significance of the interaction between microcirculation and macrocirculation in the flow-mediated dilation (FMD) is poorly understood. HYPOTHESIS: We hypothesize that baseline conduit artery vasomotor tone (CAVT) and resting microvascular resistance (MVR) predict FMD. METHODS: We investigated resting diameter and FMD of the brachial artery using high-resolution ultrasound and forearm blood flow with plethysmography in 60 healthy individuals. CAVT was calculated as change of the arterial diameter from baseline to maximal dilation expressed as percentage of the maximum dilation. Resting MVR was determined as quotient of mean arterial blood pressure and forearm blood flow. RESULTS: Mean FMD was 10.7+/-2.0%, indicating normal endothelial function. The extent of brachial artery FMD was not only related to baseline CAVT (r=0.70, P<0.01), but inversely to resting MVR (r=-0.69, P<0.01). Moreover, in a simple regression analysis, baseline CAVT was inversely related to resting MVR (r=-0.82, P<0.01). In a multivariate linear regression analysis, baseline CAVT and MVR were identified as independent predictors of brachial artery FMD. CONCLUSION: Our data imply a close interaction of resting microvascular resistance and baseline CAVT modulating flow-mediated conduit artery dilation.