Pulmonary fluid dynamics and aerosol drug delivery in the upper tracheobronchial airways under mechanical ventilation conditions

The effects of mechanical ventilation conditions on fluid flow and particle deposition were studied in a computer model of the human airways. The frequency with which aerosolized drugs are delivered to mechanically ventilated patients demonstrates the importance of understanding the effects that ventilation parameters have on particle deposition in the human airways. Past studies that modeled particle deposition in silico frequently used an idealized geometry with steady inlet conditions. With recent advancements in computational power and medical imaging capabilities, studies have begun to use more realistic geometries or unsteady inlet conditions that model normal breathing. This study focuses specifically on the effects of mechanical ventilation waveforms using a computer model of the airways from the endotracheal tube to generation 07, in the lungs of a patient undergoing mechanical ventilation treatment. Computational fluid dynamics (CFD), using the commercial software package ANSYS® CFX®, combined with realistic respiratory waveforms commonly used by commercial mechanical ventilators, large eddy simulation (LES) to model turbulence, and user defined particle force models were applied to solve for fluid flow and particle deposition parameters. The endotracheal tube (ETT) was found to be an important geometric feature, causing a fluid jet towards the right main bronchus, increased turbulence, and a recirculation zone in the right main bronchus. In addition to the enhanced deposition seen at the carinas of the airway bifurcations, enhanced deposition was also seen in the right main bronchus due to impaction and turbulent dispersion resulting from the fluid structures created by the ETT. The dependence of local particle deposition on respiratory waveforms implies that great care should be taken when selecting ventilation parameters --Abstract, page iii