Endothelial dysfunction or dysfunctions? Identification of three different FMD responses in males with type 2 diabetes

Endothelial function is widely evaluated by vasodilatation of the brachial artery induced by ischemia (flow-mediated vasodilatation, FMD). The function of the endothelium, in this setting, is to sense wall shear stress (WSS) increase and to release vasodilators. Following current guidelines FMD is measured 50-60s after ischemia. It is not known whether this lapse of time is sufficient to observe maximal vasodilatation, especially in diseased subjects. Sixty-six subjects with type 2 diabetes and 30 controls underwent FMD-test. Brachial artery WSS was measured at rest and during the first 15s after ischemia as index of peripheral resistances vessels reactivity, and FMD at 50, 120, 180, and 300s after ischemia as index of conduit vessel function. All controls exhibited increased WSS and peak FMD at 50s. Among subjects with diabetes three groups were identified based on the time at which peak FMD occurred. Twenty subjects with diabetes exhibited peak at 50s (Early FMD), 28 at 2 min (Late FMD), and 18 showed no FMD (Absent FMD). Peak FMD in Late FMD subgroup was comparable to peak in control subjects and significantly higher than peak in other subjects with diabetes. The "Absent FMD" group showed also impaired WSS. The present findings demonstrate that brachial artery response to ischemia is heterogeneous in type 2 diabetes, suggesting different mechanisms responsible for FMD alteration in this condition