Quantitative analyzes of the variability in airways via four-dimensional dynamic ventilation CT in patients with chronic obstructive pulmonary disease: correlation with spirometry data and severity of airflow limitation

Background: In chronic obstructive pulmonary disease (COPD) patients, the diagnosis and assessment of disease severity are mainly based on spirometry, which may lead to misjudgments due to poor patient compliance. Thoracic four-dimensional dynamic ventilation CT (4D-CT) provides more airway data approximating true physiological function than conventional CT. We aimed to determine dynamic changes in airways to elucidate the pathological mechanism underlying COPD and predict the severity of airflow limitation in patients.Methods: Forty-two COPD patients underwent 4D-CT and spirometry. The minimum lumen diameter changed with the breathing cycle in 4th-generation airways and was continuously measured in the apical (RB1), lateral (RB4) and posterior basal segments (RB10) of the right lung. The minimum lumen diameter in the peak inspiration and peak expiration as well as the peak expiratory/peak inspiratory ratio (E/I ratio), and dynamic coefficient of variance (CV) were calculated.Results: Correlations of FEV1% with the CV of minimum lumen diameter in RB1 (?=-0.473, P=0.002) and in RB10 (?=-0.480, P=0.005) were observed, suggesting that the dynamic variability in 4th-generation airways was associated with airflow limitation in COPD patients. The CV of the minimum lumen diameter in RB1 significantly differed between the GOLD I+II and GOLD III+IV groups [8.59 (IQR, 6.63-14.86) vs. 14.64 (10.65-25.88), respectively; P=0.016], suggesting that the dynamic CV in RB1 increased significantly in the GOLD III+IV group, which had worse pulmonary ventilation function. Based on the ROC curve analysis, CV-RB1 predicted FEV1%<50% with an optimal cut-off of 9.43% (sensitivity 85.7%, specificity 57.1%, AUC 0.717).Conclusions: 4D-CT might be an available method to help diagnose and evaluate the severity of COPD.