Aerosol transport in a breathing alveolus

Abstract

The present study aims to develop a fundamental understanding of the complex nature of fluid flow and particle transport dynamics in the alveolar region of the lungs. The acinus has a fine-scaled structure which allows for gas exchange in the blood. We model the transport characteristics of a single alveolar duct, which represents a single unit of the fine-scale acinar structure. A straight duct, with an expanding/contracting hemispherical bulb at one end, is used as a simplified approximation of a breathing alveolus. The diffusion of respiratory gases is considered across the boundary of the hemispherical bulb in order to account for the gas exchange. The transport equations are solved numerically using an Eulerian-Eulerian approach. The transport of aerosol particles could be demarcated into transient and time-periodic regimes, each with significantly different characteristics. While diffusion is observed to be the main cause of particle transport in the transient regime, the periodic nature of advective particle motion dominates in the time-periodic regime. Surprisingly, particle transport toward the acinus is observed even in a time-periodic breathing flow due to the nonlinear advective acceleration. A reduction in the particle size is observed to substantially aid the transport of aerosols. While gas exchange and increase in breathing frequency aid aerosol transport, the increase in the rate of aerosol transfer is observed to merely lower the aerosol concentration within the duct.