Three-dimensional geometric morphometric analysis of diaphragmatic dome motion in COPD patients

Diaphragmatic dysfunction is a hallmark of chronic obstructive pulmonary disease (COPD), especially in emphysema, where hyperinflation alters diaphragm geometry and impairs inspiratory mechanics. However, quantitative three-dimensional (3D) assessments of diaphragmatic dome shape and motion across COPD phenotypes are limited. This study applied 3D geometric morphometrics (3DGM) to characterize diaphragmatic kinematics and curvature in COPD patients compared to controls. We prospectively enrolled 126 adults: 40 COPD patients (17 bronchitis-predominant, 23 emphysema-predominant) and 86 asymptomatic controls. All underwent high-resolution computed tomography (CT) at functional residual capacity (FRC) and total lung capacity (TLC). Diaphragmatic form was quantified using landmark and semilandmark configurations. Curvature was estimated by fitting circular arcs to the domes. Statistical comparisons included Procrustes MANOVA, principal component analysis (PCA), and non-parametric tests. Centroid size (CS) was significantly larger in COPD, reflecting dome flattening at both lung volumes. Inspiratory size increment (ΔCS) was reduced in emphysema, particularly in females. PCA showed diminished shape change between FRC and TLC in COPD, with overlapping configurations, in contrast to distinct phases in controls. PC2 highlighted flatter domes in COPD. Curvature analysis revealed significantly larger radii in COPD, especially at TLC. In COPD, the right dome was flatter than the left, whereas controls showed the opposite. The right dome retained greater curvature change, especially in emphysema. COPD patients, particularly those with emphysema and females, exhibit diaphragmatic flattening and reduced inspiratory deformation. Asymmetrical dome behavior, with preserved right dome mobility, may reflect compensatory adaptation. 3DGM offers a valuable tool for respiratory phenotyping in COPD.