Effect of off-plane bifurcation angles of primary bronchi on expiratory flows in the human trachea

The human airway is exposed to the development of diverse flow patterns based on differences in its morphological/geometrical parameters across individuals. Although effects of the asymmetry between the right and left main bronchi on airway flows have been investigated in the past, there exists a paucity in terms of studies that focus on the role of stronger physiological asymmetric features, such as off-plane bifurcation angles of primary bronchi, in expiratory flows.

Computational fluid dynamic techniques have been used to demonstrate presence of Dean-type secondary flows and vortices in the bifurcation region. Formation of a distinctive pattern was observed corresponding to an increase in the off-plane branching angle. An experiment involving 3D printed airways and smoke was also performed to visualize flow patterns and verify simulation results.

Good agreement was observed between computational and experimental results. Furthermore, it was revealed that the predicted wall shear stress distribution demonstrated significant changes (with a maximum shear stress increase of 30.7%) compared to conventional airway models that adopt symmetric bifurcation angles. The overall flow demonstrated a swerving motion, which was characterized by tracking the vortex cores (maximum accumulated radial movement of 72.6°) when they ascended towards the trachea inlet in off-plane airway models.

It was confirmed that off-plane bifurcations in human trachea significantly alter the flow characteristics in expiratory flows. It is expected that the results of this study will provide useful information regarding increasingly advanced patient-specific treatments for respiratory diseases in the trachea.