Figure 2. Comparison of expiratory flow fields among the four models of A (Normal), B (carina tumor), C (bronchial tumor), and D (asthma).

The presence of an airway obstruction disturbs the exhaled airflow field which will further distort the trajectories of entrained particles and gives rise to different exhaled aerosol profiles. The characteristics of flow distortions depend on the location and size of the airway obstructions.