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To the Editor.—Dr Plotnick and colleagues¹ describe the use of duplex ultrasonography to determine changes in the brachial artery diameter associated with a high-fat meal. The authors claimed a significant alteration in arterial diameter, but although the differences may be statistically significant, they should not be construed as clinically significant. Based on the physics of ultrasound probes, the measurements reported by Plotnick et al are within 0.3 mm at best, presuming their machine is properly calibrated by the manufacturer. Their ultrasound machine will give caliper-derived data to within 0.1 mm. The authors report tabular data taken to the nearest 0.01 mm, based on a sample size of 20. The supposedly significant results they report are based on vasoreactivity measurements on the order of 0.2 mm. Can one really believe these data when the measured effect is less than the hidden "noise" of the machine?

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