On the mechanism of mucosal folding in normal and asthmatic airways

TLDR

Airway walls are markedly thickened in asthma and COPD, and smooth‑muscle contraction induces mucosal buckling that forms folds penetrating the lumen, potentially affecting luminal obstruction. The study aims to identify the factors that determine mucosal folding patterns and how changes in layer thickness or stiffness alter these patterns. A finite‑element two‑layer composite airway model was used to analyze how variations in layer thickness and stiffness influence mucosal folding. The analysis shows that the thickness of the thin inner layer is the most critical factor, with its thickening—mirroring subepithelial collagen deposition in asthma—producing high shear stress near the epithelium that may cause sloughing and steep pressure gradients that could shift fluid between wall compartments or the lumen.

Abstract

Previous studies have demonstrated that the airway wall in asthma and chronic obstructive pulmonary disease is markedly thickened. It has also been observed that when the smooth muscle constricts the mucosa buckles, forming folds that penetrate into the airway lumen. This folding pattern may influence the amount of luminal obstruction associated with 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 result of changes in the thickness or stiffness of the different layers that comprise the airway wall. Results demonstrate that the most critical physical characteristic is the thickness of the thin inner layer of the model. Thickening of this inner layer likely is represented by the enhanced subepithelial collagen deposition seen in asthma. Other findings show a high shear stress at or near the epithelial layer, which may explain the pronounced epithelial sloughing that occurs in asthma, and steep gradients in pressure that could cause significant shifts of liquid between wall compartments or between the wall and luminal or vascular spaces.