Three-Dimensional Convective Alveolar Flow Induced by Rhythmic Breathing Motion of the Pulmonary Acinus

Abstract

Low Reynolds number flows (Re<1) in the human pulmonary acinus are often difficult to assess due to the submillimeter dimensions and accessibility of the region. In the present computational study, we simulated three-dimensional alveolar flows in an alveolated duct at each generation of the pulmonary acinar tree using recent morphometric data. Rhythmic lung expansion and contraction motion was modeled using moving wall boundary conditions to simulate realistic sedentary tidal breathing. The resulting alveolar flow patterns are largely time independent and governed by the ratio of the alveolar to ductal flow rates, Qa/Qd. This ratio depends uniquely on geometrical configuration such that alveolar flow patterns may be entirely determined by the location of the alveoli along the acinar tree. Although flows within alveoli travel very slowly relative to those in acinar ducts, 0.021%<or=Ua/Ud<or=9.1%, they may exhibit complex patterns linked to the three-dimensional nature of the flow and confirm findings from earlier three-dimensional simulations. Such patterns are largely determined by the interplay between recirculation in the cavity induced by ductal shear flow over the alveolar opening and radial flows induced by wall displacement. Furthermore, alveolar flow patterns under rhythmic wall motion contrast sharply with results obtained in a rigid alveolus, further confirming the importance of including inherent wall motion to understand realistic acinar flow phenomena. The present findings may give further insight into the role of convective alveolar flows in determining aerosol kinematics and deposition in the pulmonary acinus.

CFD investigation of respiratory flows in a space-filling pulmonary acinus model

“…3). Hence, alveolar flow patterns are determined by the interplay between shear flow over alveolar mouths, leading to recirculation, and radial streamlines induced by wall motion, as noted previously [6][7][8]15]. As one travels towards regions where the strength of the ductal flow decreases, recirculation regions disappear and fluid fills alveolar cavities in a radial fashion ( fig.…”

“…For this, we increased the density of volume elements by approximately 30% above the value that was eventually used (~540'000 elements). To achieve sufficiently accurate results such that changes in the resulting entrance flow Re were within <5% upon further time step refinement, a time step of ∆t=T/200 was eventually implemented [15]. Lagrangian trajectories of fluid (or massless) particles,…”

Investigation of the Effects of Emphysema and Influenza on Alveolar Sacs Closure through CFD Simulation

“…The continuity equation represents the conservation of mass, Equation (1), and the Navier-Stokes equations represent the conservation of momentum, Equation (2), that would be solved numerically on a moving grid using a commercial finite-volume based …”

“…They concluded that the ratio of duct volume to cavity volume would be an effective parameter of flow patterns in alveolar sacs. Sznitman et al [2] considered rhythmic breathing motion of the pulmonary acinus and simulated induced air flow through the model of the alveolated ducts at each generation of the pulmonary acinar tree. They demonstrated the importance of three dimensional (3D) simulations in investigating existing complex flow patterns in alveolar sacs.…”

High resolution tomographic imaging of the alveolar region of the mammalian lung

“…Several collaborators used the extracted datasets for simulating the airflow [143,144] and particle deposition [145] in the terminal airways.…”