Liquid plug formation in an airway closure model

Human lung airways are lined with a liquid made out of mucus and serous layers. In small airways, the surface tension between this liquid layer and the air can induce a Plateau-Rayleigh instability. In order to study this, we model the airway as a rigid pipe coated internally with a Newtonian liquid. Our numerical simulations are based on the VOF method, employed to simulate the interfacial instability from initiation to coalescence and plug formation. This event closes the airway. Our parametric study considers relevant conditions for healthy or pathological situations. It demonstrates that the plug formation induces a high level of stress and stress gradients on the pipe walls, where epithelial cells cover the airways. We find that post-coalescence wall stresses can be 300% to 600% greater than pre-coalescence values. Hence, airway closure qualifies as a cause of sub-lethal or lethal damage to the epithelial cells, which provokes biological response.