The lung loses its elasticity and therefore these areas of the lungs become enlarged. The loss of elasticity limits airflow out of the lung. An estimated 2 million Americans have emphysema. Although the causes of COPD are not fully understood, it is generally agreed that the most important cause is cigarette smoking. Causes such as air pollution and occupational exposures may play a role especially when combined with cigarette smoking.
Heredity plays a role in some patient's emphysema.
It is well known that cancer and COPD are closely related. It has now been shown that patients with airflow obstruction have a higher incidence of cancer of the lung than those without obstruction. COPD is the fourth leading cause of death in the United States. The most common symptoms of chronic bronchitis include cough and sputum. After many years, the patient develops shortness of breath.