Entry of air in the pleural cavity is called pneumothorax. It may be spontaneous, result of penetrating or non-penetrating injuries.
Caused by blunt injury resulting in fractured ribs piercing the pleural membrane or by a sudden compression of the rib cage. Air enters the pleural space increasing intra pleural pressure which collapse the lung.
Result from the rupture of an emphysematous bleb on the lung surface or that may follow severe bouts of coughing in persons with pulmonary disease.
When air leak into the intra pleural space and it cannot escape during expiration. This can be a result-of closed pneumothorax and also of penetrating chest injury. The accumulated air buildup positive pressure in the chest cavity resulting in lung collapse on the affected side, mediastinal shift towards unaffected side and compression of mediastinal organs resulting in decreased cardiac output and decreased venous return,