Tension Pneumothorax

This illustration shows a tension pneumothorax, which develops when a lung injury (shown in the illustration as a small dark area on the left lung) or chest wall injury acts as a one-way valve mechanism that allows air into the space between the chest wall and lung (pleural space) but not out of it. (Small black arrows indicate air leaking out of the lung; large black arrows indicate pressure from air in the pleural space.) As a result, air accumulates and compresses the lung, eventually shifting the structures in the middle of the chest to the other side, including the heart and trachea; compressing the other lung; and decreasing the flow of blood returning from the body to the heart through the veins. This can cause shock, a life-threatening condition.