Limitations of non-invasive endothelial function assessment by brachial artery flow-mediated dilatation

A non-invasive technique using high-frequency ultrasound brachial artery imaging to assess endothelium-dependent flow-mediated vasodilatation is a widely used test, but interpretation of results is not consistent. This study was designed to assess the method of non-invasive endothelial function determination of a brachial artery. Endothelial function was assessed by two physicians in 18 young, healthy volunteers. Each volunteer was examined by both physicians on the same day using an identical protocol; a second assessment was carried out at an interval of 6-7 days. When comparing arterial dilatation at first and second measurements by one physician, there were no statistically significant differences (first physician: 5.95 +/- 2.93% versus 7.63 +/- 4.3%; P = 0.21; second physician: 4.23 +/- 1.6% versus 4.94 +/- 2.69%; P = 0.22). Further, we found statistically significant differences in artery dilatation when comparing measurements made separately by both physicians on the same day (5.95 +/- 2.93% versus 4.23 +/- 1.6%; P = 0.03, and 7.63 +/- 4.3% versus 4.94 +/- 2.69%; P = 0.003). Our results suggest a large inter-individual variability of measurements within the whole group, if made on the same day and at the same time by two physicians. On the contrary, no significant differences were noted when comparing measurements of the whole group by the one physician at an interval of 1 week. It can be concluded that the degree of brachial artery flow-mediated dilatation is difficult to evaluate on the basis of a predefined cut-off point as a single-measurement screening test.