A physical model for small airway closure is developed, based on the assumption that
closure occurs as a result of a surface tension-induced instability of the thin liquid film lining
the airways. To distinguish this mechanism from others involving airway compliance,
experiments were performed in rigid tubes, 1 mm in diameter, with length-to-diameter ratios
between one and ten. Oil was added to the film in small increments and photographed at
each stage. For total liquid volumes (V) less than some critical value (V c) surface tension …