[Characteristics of pathophysiology in COPD].

Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation caused by emphysema and/or airway narrowing. The major site of airflow limitation in COPD is thought to be small airways (inner diameters<2 mm). In patients with COPD, FEV1 (%predicted) is highly correlated with airway luminal area and also with wall thickening and the correlation coefficients improve as airway size decreases. In patient with COPD, maximal flow(V max) at lower lung volumes is remarkably lowered. As the disease progresses, air trapping occurs even during resting ventilation, thus causing increased functional residual capacity (FRC). Reduced inspiratory capacity as a result of increased FRC is believed to be highly correlated with breathlessness in COPD.