Figure 1.

.Schematic of the RT. (A) The nasal and lower RT network (excluding pharynx and larynx) idealized as cylinders plus the alveolar space. (B) Cylindrical airways are multilayered: luminal airspace, mucus layer with variable thickness and advection velocity, uniform 7 μm, nonadvecting, periciliary liquid layer (PCL), and epithelial cells/tissue. (C) The cylindrical generations can be locally unfolded to a rectangular geometry, with x, y, and z coordinates as shown. Note that the ratio of mucus to PCL thickness shown is highly variable, so that (B) and (C) are loosely representative of generation 10 of the lower RT.