ON THE MECHANISM OF MUCOSAL FOLDING IN NORMAL AND ASTHMATIC AIRWAYS

Previous studies have demonstrated that the airway wall in asthma and chronic obstructive pulmonary disease is markedly thickened. It has al so been observed that when the smooth muscle constricts the mucosa buc kles, forming folds that penetrate into the airway lumen. This folding pattern may influence the amount of luminal obstruction associated wi th smooth muscle activation. A finite-element analysis of a two-layer composite model for an airway is used to investigate the factors that determine the mucosal folding pattern and how it is altered as a resul t of changes in the thickness or stiffness of the different layers tha t comprise the airway wall. Results demonstrate that the most critical physical characteristic is the thickness of the thin inner layer of t he model. Thickening of this inner layer likely is represented by the enhanced subepithelial collagen deposition seen in asthma. Other findi ngs show a high shear stress at or near the epithelial layer, which ma y explain the pronounced epithelial sloughing that occurs in asthma, a nd steep gradients in pressure that could cause significant shifts of liquid between wall compartments or between the wall and luminal or va scular spaces.