(A) This graphic is a representation of dynamic computed tomography of the airway which is taken at the end of forced expiration. It shows a bowing of the posterior tracheal wall, a small anteroposterior airway diameter, and an increase in lung attenuation. All of these features are consistent with tracheomalacia. (B) To calculate the collapsibility index (CI), the dynamic expiratory area (DEA; C) is subtracted from the area at end inspiration (AEI; B) and this number is then divided by the AEI and multiplied by 100. CI = (AEI-DEA/AEI) × 100, which in this case is 53.4%.
