Why does a pneumothorax cause a lung to collapse?
A collapsed lung (pneumothorax) is a buildup of air in the space between the lung and the chest wall (pleural space). As the amount of air in this space increases, the pressure against the lung causes the lung to collapse. This prevents your lung from expanding properly when you try to breathe in, causing shortness of breath and chest pain. A pneumothorax may become life-threatening if the pressure in your chest prevents the lungs from getting enough oxygen into the blood.
