From the clinical perspective, COPD is a chronic
process of progressive airflow limitation associated with
symptoms such as cough, sputum production, and dyspnea.
Recently, the Global Initiative for Chronic Obstructive
Lung Disease defined COPD as “a disease state characterized
by airflow limitation that is not fully
reversible,” which is “progressive and associated with an
abnormal inflammatory response of the lungs to noxious
particles and gases.