Fig. 2From: Expiratory central airway collapse in stable COPD and during exacerbationsPercentage tracheal collapse in acute exacerbations of COPD and at convalescence. In the subset of patients who returned for repeat CT scans at convalescence (n = 17), tracheal collapse is similar between acute exacerbations and convalescence. Tracheal collapse was measured as the ratio of expiratory/inspiratory airway area and expressed as a percentage (%)Back to article page