Validity and reliability of assessing diaphragmatic mobility by area on X-rays of healthy subjects

OBJECTIVE: To investigate the concurrent validity, as well as the intra- and inter-rater reliability, of assessing diaphragmatic mobility by area (DM(area)) on chest X-rays of healthy adults. METHODS: We evaluated anthropometric parameters, pulmonary function, and diaphragmatic mobility in 43 participants. Two observers (rater A and rater B) determined diaphragmatic mobility at two time points. We used Pearson’s correlation coefficient to evaluate the correlation between DM(area) and the assessment of diaphragmatic mobility by distance (DM(dist)). To evaluate intra- and inter-rater reliability, we used the intraclass correlation coefficient (ICC [2,1]), 95% CI, and Bland-Altman analysis. RESULTS: A significant correlation was found between the DM(area) and DM(dist) methods (r = 0.743; p < 0.0001). For DM(area), the intra-rater reliability was found to be quite high for the right hemidiaphragm (RHD)-ICC (2,1) = 0.92 (95% CI: 0.86-0.95) for rater A and ICC (2,1) = 0.90 (95% CI: 0.84-0.94) for rater B-and the left hemidiaphragm (LHD)-ICC (2,1) = 0.96 (95% CI: 0.93-0.97) for rater A and ICC (2,1) = 0.91 (95% CI: 0.81-0.95) for rater B-(p < 0.0001 for all). Also for DM(area), the inter-rater reliability was found to be quite high for the first and second evaluations of the RHD-ICC (2,1) = 0.99 (95% CI: 0.98-0.99) and ICC (2,1) = 0.95 (95% CI: 0.86-0.97), respectively-and the LHD-ICC (2,1) = 0.99 (95% CI: 0.98-0.99) and ICC (2,1) = 0.94 (95% CI: 0.87-0.97)-(p < 0.0001 for both). The Bland-Altman analysis showed good agreement between the mobility of the RHD and that of the LHD. CONCLUSIONS: The DM(area) method proved to be a valid, reliable measure of diaphragmatic mobility.