Despite being largely associated in former days with miners who inhaled coal dust from primitive pit conditions, nowadays many cases of emphysema would appear to be caused by cigarette smoking. Atmospheric pollution is sometimes still a predisposing factor and, in rare cases, emphysema is inherited, but in the main this painful and often fatal disease is attributed to inhaling tobacco smoke. However, many sufferers have never smoked and many heavy smokers do not develop emphysema. This may mean that there is another primary cause of the disease. Emphysema is a disease in which the alveoli (tiny air sacs) in the lungs become damaged. This, in turn, leads to shortness of breath and, in severe cases, to respiratory failure or heart failure. In order to understand the progress of the disease, it helps to know a little about the mechanics of breathing. Firstly, the role of the all-important alveoli: inhaled oxygen is passed into the bloodstream and carbon dioxide is removed from capillaries to be breathed out through the walls of the alveoli which line the lungs. Tobacco smoke and other pollutants provoke the alveoli to release chemicals that damage their walls. As the damage gets progressively worse, the oxygen and carbon dioxide exchange is impaired, making the lungs progressively less efficient. Eventually, the level of oxygen in the blood falls, with one of two effects. Either pulmonary hypertension develops, leading to cor pulmonale (enlargement and strain on the right-and side of the heart) and subsequently to oedema (accumulation of fluid in tissues), particularly in the lower legs; or patients compensate for the loss of oxygen by breathing faster. Unfortunately, however much a sufferer tries to compensate by breathing more rapidly, if the condition is left untreated and/or a patient continues to smoke, they will find it increasingly difficult to breathe. Emphysema is often accompanied by chronic bronchitis, which is also brought on by smoking and air pollutants.