Fig. 2.

Airway segments and acini labeled according to gas transport mechanisms. A: decision trees used for labeling airway segments according to the dominant gas transport mechanism contributing to the overall rate of gas transport within each individual airway. Acini are labeled if fresh gas is advected via bulk flow directly into the acinar space. B: airways and acini colored according to gas transport mechanisms during eucapnic ventilation at various frequencies using the tidal volumes indicated in milliliters. Acini that do not receive fresh gas ventilation are not shown. Gravitational direction (g) is indicated for a supine orientation.