Intrathoracic Tracheal Volume and Collapsibility on Inspiratory and End-expiratory CT Scans: Correlations with Lung Volume and Pulmonary Function in 85 Smokers

Rationale and Objectives: To evaluate the correlations of tracheal volume and collapsibility on inspiratory and end-expiratory computed tomography (CT) with lung volume and with lung function in smokers. Materials and Methods: The institutional review board approved this study at each institution. 85 smokers (mean age 68, range 45-87 years; 40 females and 45 males) underwent pulmonary function tests and chest CT at full inspiration and end-expiration. On both scans, intrathoracic tracheal volume and lung volume were measured. Collapsibility of the trachea and the lung was expressed as expiratory/inspiratory (E/I) ratios of these volumes. Correlations of the tracheal measurements with the lung measurements and with lung function were evaluated by the linear regression analysis. Results: Tracheal volume showed moderate or strong, positive correlations with lung volume on both inspiratory (r = 0.661, P < .0001) and end-expiratory (r = 0.749, P < .0001) scans. The E/I ratio of tracheal volume showed a strong, positive correlation with the El ratio of lung volume (r = 0.711, P < .0001). A weak, negative correlation was found between the E/I ratio of tracheal volume and the ratio of forced expiratory volume in the first second to forced vital capacity (r = -0.436, P < .0001). Also, a weak, positive correlation was observed between the Ell ratio of tracheal volume and the ratio of residual volume to total lung capacity (r = 0.253, P = .02). Conclusions: Tracheal volume and collapsibility, measured by inspiratory and end-expiratory CT scans, is related to lung volume and collapsibility. The highly collapsed trachea on end-expiratory CT does not indicate more severe airflow limitation or air-trapping in smokers.