air in the pleural cavity. Any breach of the lung surface or chest wall allows air to enter the pleural cavity, causing the lung to collapse. The leak can occur without apparent cause, in otherwise healthy people (spontaneous pneumothorax), or result from injuries to the chest (traumatic pneumothorax). In tension pneumothorax a breach in the lung surface acts as a valve, admitting air into the pleural cavity when the patient breathes in but preventing its escape when he breathes out. This air must be let out by surgical incision.
A former treatment for pulmonary tuberculosis - artificial pneumothorax - was the deliberate injection of air into the pleural cavity to collapse the lung and allow the tuberculous areas to heal.