ANATOMICAL VARIATION IN DIAPHRAGM THICKNESS ASSESSED WITH ULTRASOUND IN HEALTHY VOLUNTEERS

of the diaphragm in the zone of apposition has become increasingly popular to eval-uate muscle thickness and thickening fraction. However, measurements in this anatomical location are frequently hindered by factors that constrain physical accessibility or that alter diaphragm position. Therefore, other ana-tomical positions at the chest wall for transducer placement are used, but the variability in diaphragm thickness across the dome has not been systematically studied. The aim of this study was to evaluate anatomical variation of diaphragm thickness in 46 healthy volunteers on three ventrodorsal lines and two craniocaudal positions on these three lines. The intraclass correlation coefficient (ICC) for diaphragm thickness in the craniocaudal direc-tion on the mid-axillary line was significantly higher than those on the posterior axillary and midclavicular lines, suggesting it had the lowest variability (ICCmidaxillary = .89, 95% confidence interval [CI]: 0.83 - 0.93, ICCposterior axillary = 0.74, 95% CI: 0.62?0.85, ICCmidclavicular = 0.62, 95% CI: 0.43 - 0.47,p < 0.05). Average diaphragm thick-ness was comparable on the posterior axillary and midaxillary lines and substantially larger on the midclavicular line (1.24 mm [1.06?1.47], 1.27 mm [1.10 - 1.42] and 2.32 [1.97 - 2.70], p < 0.01). We conclude that the normal diaphragm has a large variability in thickness, especially in the ventrodorsal direction. Variability in craniocau-dal position is the lowest at the midaxillary line, which therefore appears to be the preferred site for diaphragm thickness measurement. (E-mail: m.haaksma@amsterdamumc.nl) (C) 2022 The Author(s). Published by Elsevier Inc. on behalf of World Federation for Ultrasound in Medicine & Biology.