European Respiratory Society Monograph, Vol. 59. 2013
COPD is a common and progressive chronic inflammatory condition that is responsible for a large amount of morbidity and mortality globally, and affects millions of people worldwide. It is now recognised that COPD is a heterogeneous disease and that the severity of the airflow obstruction, as determined by the forced expiratory volume in 1 second (FEV1), is not the best determinant of the severity of COPD and its impacts. Thus, severity of this disease is now determined by the combination of symptoms, future risk that is mainly related to exacerbation frequency, and FEV1 stage.