Impaired flow-mediated vasodilation in type 2 diabetes: lack of relation to microvascular dysfunction.

A reduced availability of nitric oxide (NO) is an important feature of endothelial dysfunction occurring early in the course of type 2 diabetes. The measurement of flow-mediated dilation (FMD) of the brachial artery after forearm ischemia is supposed to be a non-invasive method to assess endothelial production and release of NO. The impairment of reactive hyperemia due to microvascular dysfunction in diabetes might cause an insufficient increase in shear stress stimulating the endothelial NO release, thus leading to an underestimation of FMD. Therefore, the aim of the present study was to investigate the relationship between microcirculatory disturbances and the impairment of FMD in type 2 diabetic patients. 63 type 2 diabetic patients and 44 non-diabetic control subjects were investigated. Capillary blood cell velocity (CBV) was assessed at the dorsal middle phalangeal area of the left ring finger. Lumen diameter of the brachial artery was measured by high-resolution ultrasound. Patients were investigated at rest and after 5-min suprasystolic arterial compression. Percentage change of CBV during reactive hyperemia (CBV%) and flow-mediated dilation (FMD%) of the brachial artery relative to the baseline measurement were calculated. CBV% (63.4+/-10.7% vs. 124.0+/-18.5%; p<0.01) and FMD% (3.8+/-0.8% vs. 6.9+/-0.9%; p<0.01) were reduced in the diabetic patients compared to their control subjects. FMD% was not related to CBV% (r=0.14; p=0.139). The lack of an association between the reduction of endothelium-dependent vasodilation of the brachial artery and the impairment of postocclusive microvascular hyperemia observed in the present study contradicts the assumption that a reduced FMD is only the consequence of an impaired reactive hyperemia due to microvascular dysfunction. It also lends support to the suggestion that endothelial dysfunction in conduit vessels and impaired cutaneous microvascular responses to reactive hyperemia might at least partly develop independently due to several differences in their pathogenesis.