Chronic obstructive pulmonary disease (COPD) is an umbrella term for a group of respiratory tract diseases that are characterized by airflow obstruction or limitation. The most common cause is tobacco smoking, but COPD can also be caused by exposure to other airway irritants like coal dust or solvents. In some cases there are no known causes (idiopathic COPD) or the disease may arise due to congenital defects. COPD is a progressive disease. Obstructive changes in spirometry and decreases in diffusion capacity are typically seen before symptoms occur. Early signs and symptoms are shortness of breath on exertion, recurrent respiratory infections or a morning cough.