Chronic obstructive pulmonary disease (COPD) is a chronic progressive disorder of the lungs with high global morbidity and mortality [1]. The burden and prevalence of COPD are increasing likely due to a combination of factors including increased life expectancy, population growth and ageing, and behavioral and environmental factors (e.g., smoking and air pollution), [1]. COPD is a heterogeneous disease characterized by a persistent airflow obstruction which is usually gradual and irreversible [2].
