ABSTRACT
Chronic obstructive pulmonary disease (COPD) is defined as a progressive respiratory disease characterized by airflow limitation that is not fully reversible (1,2). This definition includes several distinct pathophysiologic conditions including chronic bronchitis and emphysema. Chronic bronchitis is defined clinically by the presence of a daily, productive cough for more than three months with a duration of more than two successive years; emphysema is pathologically defined by an enlargement of air spaces (3,4); abnormalities of small airways are frequently seen (5,6). Importantly, most patients have features of all three of these pathologic conditions (4).
