To date, widespread agreement on the precise definition of COPD is lacking. The American Thoracic Society (ATS) defines COPD as a disease process involving progressive chronic airflow obstruction because of chronic bronchitis, emphysema, or both.[SIZE=-1]5[/SIZE] Chronic bronchitis is defined clinically as excessive cough and sputum production on most days for at least three months during at least two consecutive years.[SIZE=-1]6[/SIZE] Emphysema is characterized by chronic dyspnea resulting from the destruction of lung tissue and the enlargement of air spaces. Asthma, which also features airflow obstruction, airway inflammation and increased airway responsiveness to various stimuli, may be distinguished from COPD by reversibility of pulmonary function deficits.[SIZE=-1]5[/SIZE]
