The stabilizing influence of parenchymal tethering on airway reopening

To elucidate the influence of parenchymal tethering, a series of reopening experiments was performed on freshly excised canine lobes in a vacuum chamber. In each experiment, a triple-lumen catheter was inserted into a non-cartilaginous airway (2-3 mm diameter) and alveolar capsules were placed on the lung surface to provide atmospheric pressure to the alveoli and measure alveolar pressure (P_alveoli). Lung volumes were set by fixing the vacuum pressure (P_vacuum), hence establishing the transpulmonary pressure (P_L=P_alveoli-P_vacuum). The airway was then collapsed by suction through one of the catheter´s three lumens. During subsequent constant-flow air delivery through the second lumen, the third lumen measured the pressure needed to reopen the collapsed airway. The authors noticed two types of distinct reopening behavior: (1) an unstable low-frequency fluttering phenomenon characteristic of small P_L in which the airway tends to recollapse after being reopened and (2) stable reopening phenomena at large P_L in which parenchymal tethering kept the airway patent after the airway pressure either forced the airway walls apart or ruptured the lining fluid meniscus.