Anafi and Wilson [34,35] consider primarily the relationship between pressure and flow due to airway constriction at maximal ASM activation in a single, terminal airway. Importantly the model includes a positive feedback loop between flow and resistance, by way of parenchymal interdependence. This is the salient feature of this model; that a terminal airway is surrounded by the paren- chyma it serves. This can be seen by examining the model equa- tions. Airway entrance pressure (Paw) and pressure in the acinus (PA) are related by