Chronic obstructive pulmonary disease (COPD) is currently the fourth cause of mortality in the world and it is predicted to rank third in the year 2020. The prevalence of COPD varies in different regions of the world, but it affects at least 10% of the adult population.According to the latest update of the global strategy for the diagnosis, management and prevention of COPD (The Global Initiative for Chronic Obstructive Lung Disease [GOLD]), it is defined as a "preventable and treatable disease with some significant extra-pulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterized by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases." This definition has several aspects that deserve specific comment.
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