Pathophysiology

Any communication between pleural cavity and atmosphere or alveoli causes movement of air into pleural space until when there is no pressure difference between them. This process creates a  one-way valve allowing air inflow into the pleural space, and prohibiting air outflow.

As a result, pressure rises within the affected hemithorax (one half of the thorax) causing ipsilateral lung collapse and hence hypoxia. Further pressure causes the mediastinum shift toward the contralateral side compressing both, the contralateral lung and the vasculature entering the right atrium of the heart (Superior and inferior vena cava). This leads to worsening hypoxia and compromised venous return