Airway stability and heterogeneity in the constricted lung

The effect of bronchoconstriction on airway resistance is known to be spati ally heterogeneous and dependent on tidal volume. We present a model of a s ingle terminal airway that explains these features. The model describes a f eedback between flow and airway resistance mediated by parenchymal interdep endence and the mechanics of activated smooth muscle. The pressure-tidal vo lume relationship for a constricted terminal airway is computed and shown t o be sigmoidal. Constricted terminal airways are predicted to have two stab le states: one effectively open and one nearly closed. We argue that the he terogeneity of whole lung constriction is a consequence of this behavior. A irways are partitioned between the two states to accommodate total flow, an d changes in tidal volume and end-expiratory pressure affect the number of airways in each state. Quantitative predictions for whole lung resistance a nd elastance agree with data from previously published studies on lung impe dance.