Chronic obstructive pulmonary disease (COPD) is defined as progressive, chronic airflow obstruction due to chronic bronchitis, emphysema, or both. The majority of patients have components of both, although one of these entities will frequently dominate the clinical picture.
Emphysema�airspace enlargement distal to the terminal bronchioles due to destruction of alveolar septa.
Chronic bronchitis�chronic airway inflammation and bronchospasm. Clinically defined as productive cough lasting for at least 3 mo over 2 consecutive years.
Although COPD is irreversible, patients with acute exacerbations do have reversible bronchospastic and inflammatory components.