Impact of shear stimulus, risk factor burden and early atherosclerosis on the time-course of brachial artery flow-mediated vasodilation

OBJECTIVES: Our aim was to analyze flow-mediated dilation (FMD) time-course in response to forearm occlusion in the clinical setting. METHODS AND RESULTS: In 50 asymptomatic subjects, monitoring software measuring continuous beat-to-beat change in brachial artery diameter was used to determine FMD magnitude in percentage change in peak diameter from baseline (FMD-DeltaD), time to peak diameter after occlusion release (FMD-t(peak)), integrated FMD response calculated as area under dilation curve (FMD-AUC), maximum FMD rate calculated as maximal slope of dilation (FMD-MDR). FMD-DeltaD and FMD-MDR correlated positively with peak wall shear stress (P < 0.05, P < 0.01). FMD-MDR correlated negatively with age (P < 0.001), Framingham risk score (P < 0.01) and carotid intima-media thickness (P < 0.05), while FMD-DeltaD correlated negatively with Framingham risk score only (P < 0.01). After adjustment, all these correlations were independent of antihypertensive, lipid-lowering and antidiabetic therapies. All but that of FMD-MDR with intima-media thickness were also found in a subgroup of 29 untreated subjects and in a subgroup of 24 untreated and low-risk (FRS < 10%) subjects. FMD-t(peak) and FMD-AUC were not associated with shear stimulus, Framingham risk score, and intima-media thickness. CONCLUSION: The kinetics of dilation (maximum rate) seem more sensitive than their magnitude in assessing FMD performance and its determinants.