Figure 1.

(A) Schematic representation of the fundamental forces—gravity, drag, and diffusion—which determine particle motion and capture in this model. (B) A general schematic for the flow division at bifurcations. The $p_{e,0}$ and $p_{e,1}$ are the escape probabilities from the 0th and 1st airway segments, which depend explicitly on the instantaneous flow through those segments as given by Eq. 7.