Final answer:
A pneumothorax occurs when air enters the pleural space through a breach in the chest wall or lung surface, leading to lung collapse. It is treated by applying suction to restore negative pressure and expand the lungs.
Step-by-step explanation:
A pneumothorax results when an injury allows air to enter through a hole in the chest wall or the surface of the lung as the patient attempts to breathe, causing the lung on that side to collapse. This condition can be associated with a spontaneous pneumothorax, connected to subtle abnormalities in connective tissue, or caused by more direct punctures to the lung area. The gauge pressure in the liquid attaching the lungs to the inside of the chest wall is typically negative, and when air enters the chest cavity, it disrupts this balance, leading to the collapse of the lung(s). Suction is often applied in medical settings to reestablish negative pressure and re-inflate the lungs.