Emphysema. Specimen of sectioned human lung tissue diseased with pulmonary emphysema. At left is the affected lung area (black) with severe lung damage at far left. Normal lung tissue is at right. The scale reference is in centimetres. Emphysema is a disease in which the tiny air sacs (alveoli), the sites of gas exchange, become enlarged & the walls separating them damaged. As here, the walls may collapse. As a result carbon dioxide builds up in the blood and oxygen uptake is restricted, leading to breathlessness, wheezing, bluish skin and a chronic cough. Emphysema is usually caused by smoking. The disease is incurable, & if extensive areas of lung are damaged, death usually results.