Surface forces in respiratory bronchioles during a first breath-model experiment and some theoretical considerations

In a physical sense the terminal bronchioles are capillaries, and the air-liquid interface descending through them during the first breath will therefore have a spherical curvature with a radius identical to that of the airway. Air will reach the alveolus if the liquid-coated bronchiolar wall proximal to the air-liquid interface can withstand the pressure gradient required to push the interface towards the periphery. Otherwise, there is a risk that the bronchioles become overexpanded while the alveoli remain non-aerated.