What is chronic obstructive pulmonary disease (COPD)? Chronic obstructive pulmonary disease (COPD) is a preventable and treatable disease characterized by airflow limitation that is not fully reversible, progresses, and is associated with an abnormal inflammatory response of the lungs to harmful gases or harmful particles such as cigarette smoke. COPD primarily involves the lungs, but can also cause systemic (or extrapulmonary) adverse effects. Pulmonary function tests are important in determining airflow limitation. After inhalation of bronchodilators, a first second exertional expiratory volume (FEV1)/exertional spirometry (FVC) <70% indicates the presence of airflow limitation and is not fully reversible. COPD is closely associated with chronic bronchitis and emphysema. COPD is diagnosed in patients with chronic bronchitis and emphysema when airflow limitation is present on pulmonary function tests and is not completely reversible. The pathogenesis of COPD is not fully understood, and it is generally accepted that COPD is characterized by chronic inflammation of the airways, lung parenchyma, and pulmonary vasculature. Inhalation of harmful particles or gases can cause inflammation in the lungs, and smoking can induce inflammation and directly damage the lungs.