Asthma is traditionally viewed as a disease in which airway reactivity and resistance are increased. However, the elastic component of breathing pressure increases almost as much as the resistive component. Contemporary models of the constricted lung attribute the increase in dynamic lung elastance to heterogeneous airway constriction. Measurements of gas mixing, alveolar capsule data, and direct visualization of the airways all confirm non-uniform airway resistance.; Bronchoconstriction primarily affects the peripheral lung, and the aim of this thesis is to explain the heterogeneous properties of the constricted lung by modeling the mechanics of a constricted terminal airway. During breathing, airways are periodically stretched through their connection with the surrounding parenchyma. The airway model includes both the constitutive properties of periodically stretched smooth muscle, and the feedback between airway resistance and parenchymal tethering. The model airway is shown to be bi-stable, and heterogeneous constriction is thus an inherent consequence of airway mechanics.; Lung impedance and gas mixing change systematically with both imposed tidal volume and the degree of smooth muscle activation. The model is used to predict these changes and model predictions are compared to both new and previously published experimental data. Finally, an empirical mathematical model for the dynamic behavior of airway smooth muscle is presented.
展开▼
