The effect of lobar collapse on the distribution of free intrapleural air.

In patients with pneumothorax, the normal lung tends to maintain its original shape because its retractility is more or less uniform. Lobar collapse leads to a localized increase in the force of retraction and a greater tendency of air to collect in the overlying pleural space, sometimes leading to an unusual distribution of pleural air. Four cases of pneumothorax in supine patients with lobar collapse are presented. Knowledge of the factors governing the distribution of free pleural air is of value in the early detection of pneumothorax. In the presence of lobar collapse, and probably any degree of atelectasis secondary to airway obstruction, an unusual distribution of air should be expected.