High Quality Content by WIKIPEDIA articles! A tension pneumothorax is a life-threatening condition that results from a progressive deterioration and worsening of a simple pneumothorax, associated with the formation of a one-way valve at the point of a rupture in the lung. Air becomes trapped in the pleural cavity between the chest wall and the lung, and builds up, putting pressure on the lung and keeping it from inflating fully. Upon inspiration, when the pressure inside the chest and pleural cavity falls as a result of the respiratory muscles increasing chest dimensions, air is sucked in through the one way valve, into the pleural space.