LAUSR

This study aims to introduce a 1-D computational fluid dynamics (CFD) model for airway resistance and lung compliance to examine the relationship between airway resistance, pressure, and regional flow distribution. We employed five healthy and five asthmatic subjects who have dynamic CT scans (4-D CT) along with two static scans at total lung capacity and functional residual capacity. Fractional air-volume change (ΔVairf) from 4-D CT was used for a validation of the 1-D CFD model. We extracted diameter ratio from existing datasets of 61 healthy subjects for computing mean and standard deviation (SD) of airway constriction/dilation in CT-resolved airways. The lobar mean (SD) of airway constriction/dilation was used to determine diameters of CT unresolved airways. An 1-D isothermal energy balance equation was solved, and pressure boundary conditions were imposed at the acinar region (Model A) or at the pleural region (Model B). A static compliance model was only applied for Model B to link acinar and pleural regions. The values of 1-D CFD-derived ΔVairf for Model B demonstrated better correlation with 4-D CT-derived ΔVairf than Model A. In both inspiration and expiration, asthmatics with airway constriction show much greater pressure drop than healthy subjects without airway constriction. This increased transpulmonary pressures in the asthmatics, leading to an increased work-load (hysteresis). The 1-D CFD model was found to be useful in investigating flow-structure, lung hysteresis, and pressure distribution for healthy and asthmatic subjects. The derived flow distribution could be used for imposing boundary condition of 3-D CFD.