Curvature-driven transport of thin Bingham fluid layers in airway bifurcations

We uncover and study a physical process that is hidden in the healthy lung. This process can be triggered by the thickening of the thin layer of mucus lining the bronchi walls. At the air-mucus interface, surface tension and curvature can combine to oppose the physiological motion of mucus induced by cilia, causing mucus to stall or, even, move in reverse. Representing mucus as a Bingham fluid, we characterize analytically the fluid dynamics in the thin layer using dimensionless quantities and employ numerical simulations to compute the layer velocity field in airways bifurcations. This work sheds new light on the intricate workings of the respiratory system.