Diaphragm dome height on chest radiography as a predictor of dynamic lung hyperinflation in COPD

Background and objective Dynamic lung hyperinflation (DLH) can play a central role in exertional dyspnoea in patients with COPD. Chest radiography is the basic tool for assessing static lung hyperinflation in COPD. However, the predictive capacity of DLH using chest radiography remains unknown. This study was conducted to determine whether DLH can be predicted by measuring the height of the right diaphragm (dome height) on chest radiography. Methods This single-centre, retrospective cohort study included patients with stable COPD with pulmonary function test, cardiopulmonary exercise test, constant load test and pulmonary images. They were divided into two groups according to the median of changes of inspiratory capacity (Delta IC=IC lowest - IC at rest). The right diaphragm dome height and lung height were measured on plain chest radiography. Results Of the 48 patients included, 24 were classified as having higher DLH (Delta IC <=-0.59 L from rest; -0.59 L, median of all) and 24 as having lower DLH. Dome height correlated with Delta IC (r=0.66, p<0.001). Multivariate analysis revealed that dome height was associated with higher DLH independent of % low attenuation area on chest computed tomography and forced expiratory volume in 1 s (FEV1) % predicted. Furthermore, the area under the receiver operating characteristic curve of dome height to predict higher DLH was 0.86, with sensitivity and specificity of 83% and 75%, respectively, at a cut-off of 20.5 mm. Lung height was unrelated to Delta IC. Conclusion Diaphragm dome height on chest radiography may adequately predict higher DLH in patients with COPD.