Convective and Diffusive Flows in a Rhythmically expanding Alveolus

Abstract

The study of periodical flows in pulmonary acinus is of great importance for medical purposes. This paper numerically explores physics of periodical flows in a three-dimensional alveolus model with axial symmetry. Expansion and contraction of the alveolus are simulated by setting a conceptual permeable wall as the outer surface of the model and adjusting the boundary conditions in order to match continuity of the flow. For fast and normal breathing conditions, we locate the boundary between convective and diffusive flow regions at small time steps. At fast breathing the boundary of the convective region goes deeper inside the alveolus than at normal breathing, therefore reducing the resistance to aerosol and oxygen diffusion towards the alveolar surface. This issue is especially important for transport and deposition of viruses, bacteria, pollutants and aerosolized drugs deep in the alveolus.