Assessment of the reproducibility of the indirect ultrasound method of measuring diaphragm mobility.

The aim of this study was to assess the reproducibility of the ultrasound (US) measurement of craniocaudal displacement of the left branch of the portal vein as an indirect method of measuring right hemidiaphragm mobility in healthy young adults. Forty-one healthy participants were selected, ranging from 20 to 30 years of age. The US tests were conducted and interpreted by two observers (A and B) on two separate occasions (Test 1 and Test 2). Intra-observer and interobserver reproducibility and repeatability of US measurements were determined by the intraclass correlation coefficient (ICC[2,1] ) using a 95% confidence interval (CI). Interobserver reproducibility assessment showed 'high correlation' for Test 1 and Test 2 (ICC[2,1]  = 0·83, 95% CI = 0·70-0·91, and ICC[2,1]  = 0·79, 95% CI = 0·61-0·89, respectively). Intra-observer reproducibility assessment showed 'moderate correlation' for observer A (ICC[2,1]  = 0·69, 95% CI = 0·45-0·84) and for observer B (ICC[2,1]  = 0·65, 95% CI = 0·39-0·81). Repeatability assessment showed 'high correlation' for all tests performed (ICC[2,1]  = 0·86, 0·80, 0·74, 0·79, P<0·001). In conclusion, US measurement of craniocaudal displacement of the left branch of the portal vein is a reproducible method of measuring right hemidiaphragm mobility in healthy young adults.