Measurement of Flow-Mediated Vasodilation of the Brachial Artery : A Comparison of Measurements in the Seated and Supine Positions

Background Measurement of flow-mediated vasodilation (FMD) is used to assess endothelial function in humans and according to the guidelines, subjects must remain supine during the study. However, measurement of FMD while seated would be more comfortable and convenient for patients, so the purpose of this study was to determine the effect of the patient's position on FMD results. Methods and Results High-resolution ultrasonography, a linear array transducer (13 MHz) and an arm-holding device were used to measure arterial diameter in response to reactive hyperemia (FMD, cuff inflated to 50mmHg above systolic blood pressure for 5min) and in response to sublingual nitroglycerine (NTG, 75μg) in 31 subjects, which included those with cardiovascular diseases. There was no significant difference between basal or peak hyperemic blood flow in the seated or supine position. Basal brachial artery diameter, FMD and vascular response to NTG were similar in both positions (basal diameter: 3.8±0.4 vs 3.9±0.4mm, FMD: 7.3±4.3% vs 7.2±4.5%, NTG: 13.1±5.1% vs 12.8±5.6%). Conclusions The findings suggest that measurement of FMD in the seated position is as useful as measuring it in the supine position for assessing endothelial function. This flexibility of position is better for patients and physicians, and should lead to more widespread measurement of FMD.