Modeling and Simulation of Lipid Monolayers as Surfactant in Lung Alveoli

The concave cellular surface inside lung alveoli is covered by a thin water film with surfactant on top, whose continued preservation is essential for the rapid oxygen and carbon dioxide exchange between air and lung tissue. Therefore, in order to guarantee film stability during the regular breathing cycle of inhalation (expansion of lung alveoli) and exhalation (their compression), the surfactant lipid-protein layer must possess strong adaptive properties. This becomes even more important in events of sudden expansion or compression of the lung, for example, while coughing. On one hand, the function of the surfactant layer is to strongly reduce surface tension for minimizing the work of breathing, which is achieved by forming highly ordered monolayers of amphiphilic lipid molecules. On the other hand, the layer has to be fluid enough to cover the expanding surface in a continuous and rapid fashion, which requires stochastic mobility of the lipid molecules.