Emphysema. X-ray of the chest of a patient with bullous emphysema. There are large areas of trapped air (black) in the top of the right lung (left) and the top and middle right of the left lung (right). Emphysema causes the tiny air sacs of the lungs to become damaged, leading to the walls between them breaking down. This causes large areas of trapped air and leads to a smaller surface area for gaseous exchange, restricting oxygen uptake by the blood. Enlarged air spaces bigger than 1 centimetre in diameter are known as bullae. Lung tissue in bullae may be completely destroyed. The main cause of emphysema is cigarette smoking. Symptoms include a cough and shortness of breath. Bullae may be surgically removed although there is no cure for emphysema.