Chronic Obstructive Pulmonary Disease (COPD) is a common clinical problem. It is also known by various other names, such as Chronic Obstructive Lung Disease (COLD), Chronic Obstructive Airway Disease (COAD), Chronic Airflow Obstruction (CAO), Chronic Airway (or Airflow) Limitation (CAL), or simply as Chronic Bronchitis and Emphysema.

COPD, which includes chronic bronchitis and emphysema, is a progressive disease characterized by airflow limitation/obstruction that is either not reversible at all or only partially reversible. It is generally difficult to separate out the two conditions (chronic bronchitis and emphysema), hence these are grouped together as COPD^1-4.COPD does not include asthma in which the airflow obstruction is largely reversible. The airflow obstruction in COPD is associated with abnormal inflammatory response of the lungs to chronic inhalational exposure from smokes, dusts and other air pollutants.

COPD manifests as chronic cough with or without sputum production. To define COPD, the presence of these symptoms for more than three months of a year for at least two consecutive years is considered essential. It may or may not be accompanied with progressive breathlessness. The disease progresses with time ultimately leading to respiratory disability and death.

Acute exacerbations of COPD occur whenever there is an episode of infection or some other complication. There is worsening of symptoms, deterioration of clinical condition and impairment of lung function during the period of exacerbation.