Association of Diaphragmatic Crus Thickness Assessed by Computed Tomography with Diaphragmatic Excursion and Exercise Capacity in Patients with Chronic Obstructive Pulmonary Disease

Purpose Diaphragmatic dysfunction contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). Although diaphragmatic excursion during deep breathing (DE max ) is associated with exercise capacity, the relationship between computed tomography (CT)-derived diaphragm morphology and diaphragmatic function remains unclear. We investigated the association of CT-derived diaphragmatic crus thickness with diaphragmatic excursion and exercise capacity in COPD. Methods This retrospective single-centre study included 100 patients with stable COPD who underwent chest CT, spirometry, ultrasonographic assessment of DE max , and 6-minute walk distance (6MWD) testing. Diaphragmatic crus thickness was measured on axial CT images, and the diaphragmatic thickness index (DTI) was calculated after adjustment for body mass index. Multivariable linear regression analyses were performed to identify factors independently associated with DE max and 6MWD. Patients were stratified according to DTI and DE max to evaluate combined structural and functional diaphragm phenotypes. Results In multivariable analyses, DTI was independently associated with DE max (β = 0.57, p < 0.001) and 6MWD (β = 0.25, p < 0.01) after adjustment for age, pulmonary function, and skeletal muscle indices. The combined low-DTI/low- DE max phenotype was independently associated with reduced exercise capacity (6MWD < 350 m; odds ratio 14.89, 95% confidence interval 3.51–87.89, p < 0.001). Conclusion CT-derived diaphragmatic thickness was independently associated with diaphragmatic excursion and exercise capacity in COPD. Combined structural and functional diaphragm assessment identified patients with markedly reduced exercise capacity, suggesting a role for integrated diaphragm evaluation in functional risk stratification.