Pathophysiological mechanisms of COPD

Chronic obstructive pulmonary disease (COPD) is not so much a single entity as a collection of conditions which share the feature of chronic obstruction of expiratory flow. Since COPD is a collection of conditions, a variety of pathophysiological mechanisms can contribute to varying degrees to obstruction in different patients. For example, while contraction of airways smooth muscle is generally regarded as an important mechanism underlying airflow obstruction in asthma, it can also play a role in some patients with COPD. This mechanistic overlap between asthma and COPD has led to some confusion in the clinical classification of patients. Airflow obstruction in COPD can result from mechanisms independent of smooth muscle contraction. Loss of lung elastic recoil appears to play a particularly important role in patients with pulmonary emphysema, whilst fibrosis and alteration in small airway structure appears to play an important role in patients with obstructive bronchitis. Patients with clinically significant COPD can have altered production and clearance of secretions, as well as variable degrees of airway inflammation. Finally, COPD can have variable systemic effects.