Computational Analysis of Unsteady Airway Flow Physics During Airway Pressure Release Ventilation

Airway pressure release ventilation (APRV) using the time-controlled adaptive ventilation (TCAV) method is seen to enhance proximal mucus movement relative to conventional volume-controlled ventilation (VCV), yet the airway-scale flow physics responsible for this behavior remain poorly understood. This study uses unsteady Reynolds-averaged Navier-Stokes simulations to examine how ventilator waveform timing and endotracheal tube (ETT) cuff geometry modify flow structures in an intubated tracheobronchial airway. Simulations were conducted in an idealized, asymmetric, three-dimensional Weibel airway model using three ventilation modes: assisted VCV, TCAV, and a modified high-duty-cycle VCV waveform designed to reproduce observed expiratory-biased flow conditions. Two ETT cuff geometries, representing MicrocuffTM and TaperGuardTM styles, were analyzed under identical ventilator settings to isolate cuff-induced effects. Results show that assisted VCV generates a persistent high-momentum core and large-scale recirculatory structures, producing heterogeneous shear and strong jet-wall interactions. In contrast, TCAV suppresses large-scale recirculation and promotes more organized, wall-bounded shear layers, which is associated with reduced inspiratory shear exposure and more coherent expiratory flow structures. Cuff geometry strongly modulates these dynamics: the MicrocuffTM sustains greater vortical persistence within the bronchi, whereas the TaperGuardTM produces a more ordered but less dynamically mixed flow field. Together, these results indicate that ventilator timing and cuff geometry govern airway flow organization, shear distribution, and unsteady transport characteristics. These airflow features are consistent with conditions that may be associated with secretion mobilization, although secretion transport is not directly resolved in the present simulations.