Impaired lung deformation during expiration in chronic obstructive pulmonary disease using four-dimensional...

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation and heterogeneous parenchymal destruction. Spirometry, the clinical standard, assesses global function but cannot evaluate regional lung mechanics. Four-dimensional dynamic-ventilation computer tomography (4D-CT)-based strain analysis can quantify local parenchymal deformation, yet its behavior across the full spectrum of COPD severity-particularly during the entire expiration phase in advanced disease-remains poorly characterized. This study aimed to quantitatively evaluate lung deformation patterns across COPD severities, and investigate the potential value in characterizing of strain-related parameters in cases of severe airflow limitation.

Sixty-one COPD patients who underwent spirometry and 4D-CT (three spatial dimensions plus time) were included in this study. Lung strain quantification utilized an adapted computational fluid dynamics (CFD) algorithm (MicroVec V3.6.2). Strain parameters derived from the expiration phase were adjusted for lung volume changes. Parameters from the whole expiration phase and the initial 2-s phase were compared among the Global Initiative for Chronic Obstructive Lung Disease (GOLD) I (mild), II (moderate), and III-IV (severe) airflow limitation groups using the Kruskal-Wallis nonparametric test. Correlations with the degree of airflow limitation were evaluated using Spearman analysis.

Strain parameters showed significant progressive declines with worsening GOLD stage (all P<0.05). Parameters from the whole expiration phase correlated more strongly with disease severity than those from the initial 2-s phase. Specifically, the maximum principal strain in the whole expiratory phase (P_Smax-all) exhibited the strongest inverse correlation with GOLD classification (ρ=-0.732, P<0.001), and its median value decreased over 70% in severe (GOLD III-IV) patients compared to the mild (GOLD I) group.

Decreased lung deformation during expiration was associated with loss of lung function. Strain-related parameters, especially those derived from the whole expiration phase, showed promising values in reflecting the severity of airflow limitation in patients with COPD.