Coloured computed tomography (CT) scan of the chest of a 60 year old male patient with emphysema and a long-standing collapse (atelectasis, red) of part of the right lung (left). 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. Emphysema is caused by smoking and is incurable. Treatment is aimed at preventing further damage.