Observations of time-based measures of flow-mediated dilation of forearm conduit arteries: implications for the accurate assessment of endothelial function.

Endothelium-dependent flow-mediated dilation (FMD) is measured as the increase in diameter of a conduit artery in response to reactive hyperemia, assessed either at a fixed time point [usually 60-s post-cuff deflation (FMD60)] or as the maximal dilation during a 5-min continuous, ECG-gated, measurement (FMDmax-cont). Preliminary evidence suggests that the time between reactive hyperemia and peak dilation (time to FMDmax) may provide an additional index of endothelial health. We measured FMDmax-cont, FMD60, and time to FMDmax in 30 young healthy volunteers, 22 healthy middle-aged adults, 16 smokers, 23 patients with hypertension, 40 patients with coronary artery disease, and 22 patients with heart failure. As previously reported, FMDmax-cont was similar in healthy cohorts and was significantly blunted in smokers and all patient groups, whereas FMD60 was significantly blunted only in heart failure patients. There was a wide within-group variability between measures of time to FMDmax with no significant diff...