Convective Gas Transport in the Acinus: Revisiting the Role of Effective Diffusivity

Abstract

In the pulmonary acinus, the relative importance of convection and diffusion for gas transport is often estimated using a form of the Peclet(Pe) number. This dimensionless ratio compares thebulk ductal flow velocity at an acinar generation with a diffusion velocity over a characteristic length scale. Here, we revisit the role of convection and diffusion for gas transport in the acinus using a semi-empirical analysis. We look at the significance of Taylor dispersion and consider the potential importance of oscillatory flow, under various breathing scenarios, for augmented transport in the pulmonary acinus. While some high frequency ventilation (HFV) maneuvers may lead to enhanced diffusivity, axial convection is generally not significant. The location of the diffusion front is found in more proximal generations of the acinus relative to estimates found with variations of the Pe number. These findings shed new light on the role of convection for acinar gas transport.