REPRODUCIBILITY OF BRACHIAL ULTRASONOGRAPHY AND FLOW-MEDIATED DILATATION (FMD) FOR ASSESSING ENDOTHELIAL FUNCTION

Background: High-resolution brachial artery ultrasonography is used to study vasodilator response induced by physiologic reactive hyperaemia . We examined the reproducibility of measuring flow-mediated dilatatio n (FMD) on two occasions. Aims: To determine the degree of variability of this technique in our vascular laboratory for the design of clinic al research studies. Methods: Nineteen subjects were studied on two se parate occasions using an Acuson 128 ultrasound device and a 7.0 MHz l inear array transducer. Reactive hyperaemia was induced in the brachia l artery by inflation and release of a blood pressure cuff. Nitrate-in duced dilatation was assessed in 11 of the 19 subjects. Measurements w ere made by two observers blinded to subject details. Results: The 11 subjects given sublingual GTN during the first ultrasound study had a mean nitrate-induced dilatation of 20.7% (sd 9.6). The mean vessel dia meter of 3.78 mm (sd 0.7) at rest and 3.89 mm (sd 0.7) during reactive hyperaemia yielded a mean FMD of only 3.0% (sd 2.7). The mean differe nce in FMD within-observers was 0.13% (sd 2.07), between-observers 0.0 6% (sd 2.17) and between-studies was 0.57% (sd 6.83). Conclusions: The reproducibility of FMD measured by brachial artery ultrasound was poo r and likely to render the measurements inaccurate for clinical resear ch in our hands. Between-study variation contributed the largest propo rtion of total study variability. We suggest that investigators using this technique conduct their own careful reproducibility studies in or der to avoid the misinterpretation of 'negative' studies.