Fig. 2

Difference of airway lumen area between supine and upright CT in patients with COPD. For the trachea to the 3rd-generation bronchi, the inspiratory airway lumen area was significantly larger in the standing position than in the supine position. Further, the expiratory airway lumen area was significantly larger in the standing position than in the supine position for all bronchi. Inspiratory airway lumen areas reflect airway obstruction and expiratory airway lumen areas reflect lung hyperinflation. Correlation coefficients among the airway lumen areas and lung function abnormalities were higher in the standing position compared to those in the supine position. CT, computed tomography; COPD, chronic obstructive pulmonary disease