“…Transport phenomena relevant to the thin liquid lining layer covering the luminal surface of the acinar airways are discussed elsewhere, − with extensive details on its composition and characteristics. , We recall that under normal physiological conditions, the thickness of the surfactant-rich alveolar liquid lining layer is a mere 0.1–0.2 μm and is thereby over 3 orders of magnitude smaller than the typical acinar airway dimensions. Hence, dynamic interactions that may arise between the air and liquid phase (i.e., as a resultant of boundary conditions at the fluid–fluid interface) are acknowledged to become most significant with the formation of liquid plugs ,, that fill the entire luminal space under diseased conditions (e.g., chronic obstructive pulmonary disease, cystic fibrosis, Acute Respiratory Distress Syndrome) or alternatively during surfactant replacement therapy , (SRT) and related liquid-based ventilation maneuvers. While beyond the scope of the present review, we simply comment that the past decade has witnessed important microfluidic-based efforts to investigate the propagation dynamics and rupture of liquid plugs , (including mucus plugs) in models of both single airways and bifurcating trees, ,− including the role of elevated wall shear stresses (WSS) toward epithelial cell wounding and damage. ,, …”