Methodological Approaches to Optimize Reproducibility and Power in Clinical Studies of Flow-Mediated Dilation
Ann E. Donald, AVS*,*,
Julian P. Halcox, MD, MA, FRCP*,
Marietta Charakida, MD, PhD*,
Clare Storry, BSc, AVS*,
Sharon M.L. Wallace, BA, DipHE, RN*,
Tim J. Cole, ScD ,
Peter Friberg, MD, PhD* and
John E. Deanfield, BA, BChir, MB, FRCP*
* Vascular Physiology Unit, UCL Institute of Child Health, London, United Kingdom
Centre for Pediatric Epidemiology and Biostatistics, UCL Institute of Child Health, London, United Kingdom.
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Figure 1 Image Acquisition and Readout for FMD Using B-ED and A-WT
(A) B-mode ultrasound image of the brachial artery, with region-of-interest box for edge detection diameter measurement. (B) Flow-mediated dilation (FMD) using B-mode edge detection (B-ED). (C) B-mode image with perpendicular M-line for A-mode wall tracking (A-WT). (D) A-mode wall tracking output. (Upper trace) A-mode radio-frequency signal. (Middle trace) Anterior and posterior wall motion. (Lower trace) Distension waveform generating end-diastolic diameter. AUC = area under the curve.
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Figure 2 Number of Subjects Required in Crossover and Parallel Designs for Given FMD Effect
Relation between effect on maximum percent change in flow-mediated dilation (FMD) (%) and number of subjects required in crossover and parallel study designs at 80% power and 5% significance, 4 to 6 h and 3 months apart with 3 monitoring strategies: 1, 2, or 4 measures pre- and post-treatment.
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Figure 3 Bland Altman Plots for FMD60s in Study 3 Over 1 Month Showing B-ED and A-WT
The dotted lines represent the 95% confidence intervals. The x-axis shows the average flow-mediated dilation (FMD) and the y-axis the difference between pairs. A-WT = A-mode wall tracking; B-ED = B-mode edge detection; FMD60s = change in flow-mediated dilation at 60 s after cuff deflation.
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