Influence of vessel size, age and body mass index on the flow-mediated dilatation (FMD%) of the brachial artery

Background: The non-invasive determination of the endothelial dysfunction (ED) of the brachial artery is a widely used method in clinical research. It remained, however, unclear, whether the test-results are influenced by the anatomical vessel size, the patients age, body mass index (BMI) or gender. Methods: The flow-mediated vasodilatation (FMD%) of the brachial artery was determined in 122 consecutive (88 male, 34 female) patients. FMD% was measured using high resolution ultrasound (13 Mhz) at rest, during reactive hyperaemia and after the sublingual administration of glycerolnitrate (GTN%). Results: Lumen diameters at rest varied from 2.48 mm to 6.33 mm (4.46±0.74 mm). The extent of FMD% as well as of GTN% showed an inverse correlation to the resting lumen diameters (r=−0.33, P<0.001/r=−0.51, P<0.001). This correlation was even more distinct in females (females: FMD% r=−0.54, P<0.001; GTN% r=−0.64, P<0.001 vs. males: FMD% −0.23, P<0.001; GTN% −0.59, P<0.001). No significant influence of age (61±9 years, FMD%: r=−0.04, P=0.68, GTN%: r=−0.18, P=0.05) and BMI (27.03±3.43 kg/m2, FMD%: r=0.16, P=0.08, GTN%: r=0.09, P=0.3) on the test results were found. Conclusions: FMD% was found to be rather independent of age or BMI. The anatomical vessel size had an influence on the test results, which was more obvious in female patients. Our data indicate the necessity of further methodological studies, in larger, community-based populations. In particular, it needs to be clarified, whether vessel size or even gender-specific correction factors are required when using this technique in routine clinical practice.