Click here if you prefer to see an interactive presentation of particle deposition. Downloading may take a while (85 kB).
Look at the deposition pattern of inhaled particles.
Particles of 1 µm diameter have very little mass, and hence these small particles can easily follow a turbulent flow pattern without impacting on the airway wall. However, in small airways and alveoli the linear speed approaches zero and the small distances towards the lining wall favour deposition due to sedimentation (gravitational forces) and diffusion. The proportion of 1 µm particles settling in the airway is small, and the greatest proportion is exhaled. Particles whose diameter is > 5 µm deposit preferentially in large airways as they are heavy and impact on the mucosa during directional changes in airflow. A small portion of particles > 5 µm diameter pass into the large central airways, but impact upon the mucosa of the airway wall at bifurcations of large intrathoracic airways due to their high speeds. Distal from generation 4, the total cross-sectional area of intrathoracic airways increases rapidly, the particle velocity rapidly decreases, and impaction becomes not very important for particle deposition. Now sedimentation due to gravitational forces, as well as the progressively smaller distances to the airway mucosa (diffusion) contribute increasingly towards particle clearance from inhaled and exhaled gas.