3D-measurement of tracheobronchial angles on inspiratory and expiratory chest CT in COPD: respiratory changes and correlation with airflow limitation

Purpose: To assess tracheobronchial angles and their changes on combined inspiratory and expiratory thoracic computed tomography (CT) scans and to determine correlations between tracheobronchial angles and several indices of chronic obstructive pulmonary disease (COPD). Materials and methods: A total of 80 smokers underwent combined inspiratory and expiratory CT scans. Of these, 65 subjects also performed spirometry and 55 patients were diagnosed with COPD. On CT scans, 3-dimensinal tracheobronchial angles (trachea right main bronchus [RMB], trachea deli main bronchus [LMB], and RMB-LMB) were automatically measured by software. Lung volumes at inspiration and expiration were also automatically calculated. Changes in tracheobronchial angles between inspiration and expiration were assessed by the Mann Whitney test. Correlations of the angles with lung volume, airflow limitation, and CT-based emphysema index were evaluated by Spearman rank correlation. Results: The trachea-LMB angle was significantly smaller and the RMB-LMB angle was significantly larger at expiration than inspiration (P<0.0001). The trachea-LMB and RMB- LMB angles were significantly correlated with lung volume, particularly at expiration. The RMB-LMB angle was significantly correlated with airflow limitation and CT emphysema index (P<0.001-0.05) at inspiration and expiration, suggesting that narrowed RMB-LMB angle indicates more severe airflow limitation and larger extent of emphysema. Conclusion: Tracheobronchial angles change during respiration and are correlated with severity of COPD and emphysema.