Changes in airway lumen during the respiratory cycle in tracheobronchomalacia and hyperdynamic airway collapse

The normal airway lumen during inspiration is shown with the anterior cartilaginous rings in gray and the posterior membranous tracheal wall in pale pink (A). During expiration there is inward bulging of the posterior membrane. This process is physiological and is called dynamic airway collapse (DAC) (B). The pathologic exaggeration of this process results in a reduction in cross sectional area of 70% or more and is called excessive dynamic airway collapse (EDAC) (C). In tracheobronchomalacia (TBM), a pathological collapse of the cartilaginous rings occurs. The crescent type TBM results in excessive narrowing of the sagittal (anterior-posterior) airway diameter (D). When TBM is combined with EDAC, the trachea is further flattened during expiration (E).