Pneumothorax
Air in the pleural space abolishes the negative pressure holding the lung expanded, so the lung recoils inwards, and a one-way leak raises that pressure until venous return fails.
Definition
Air in the pleural space causing partial or complete lung collapse. It is spontaneous, traumatic or iatrogenic. Spontaneous disease is primary when there is no suspected lung disease and secondary when underlying lung disease is established. It becomes a tension pneumothorax when trapped air raises pleural pressure enough to obstruct venous return.
First principles
Negative pleural pressure is the only thing keeping the lung expanded
The lung's elastic recoil pulls inwards while the chest wall springs outwards. The resulting negative pleural pressure holds the visceral and parietal surfaces together. A breach of the visceral pleura, the chest wall or a needle lets air in, abolishes the gradient, and the lung recoils.
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