Pneumothorax. Coloured chest X-ray showing the lung (orange and light blue, upper right to lower right) of a patient affected by pneumothorax. The lung at left is unaffected. Pneumothorax is a condition which arises when air (brown, centre right to lower right) is trapped between the lung and the chest wall. The lung has collapsed, which causes shortness of breath and pain on breathing. Pneumothorax can be treated by inserting a tube into the air-filled space and draining the air over a period of days. This allows the collapsed lung to re-inflate.