[Chronic obstructive pulmonary disease: definition and classification of severity].

Chronic obstructive pulmonary disease is characterized by airflow limitation that is not fully reversible and is usually both progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases, particularly tobacco smoke. Diagnosis of chronic obstructive pulmonary disease is primarily based on a reduction of forced expiratory volume in one second/forced vital capacity ratio < 70% post-bronchodilators. The characteristic symptoms of chronic obstructive pulmonary disease are cough, sputum, and dyspnea upon exertion. Based on airflow limitation as measured by spirometry, chronic obstructive pulmonary disease can be classified as mild, moderate, severe and very severe. Chronic obstructive pulmonary disease can coexist with asthma, although the inflammation characteristic of chronic obstructive pulmonary disease is distinct from that of asthma.