**2. Historical background**

COPD and its various subsets have been known in human history since pre-industrialisation era. (Snider, 1992 as cited in Shapiro SD,2010). Badham is known to have first used of the term "chronic bronchitis" in 1808(Badham,1808 as cited in Shapiro SD,2010 ). Fletcher and Laennec have presented early reviews and studies in 18th and 19th century (Fletcher et al.,1976;Laennec,1835 as cited in Shapiro SD,2010). Reid demonstrated increased mucus gland size in his pathologic studies and led to the development of the "Reid Index" and highlighted the anatomic basis for chronic bronchitis(Reid,1960).

Ruysch described enlarged respiratory air spaces on the surface of human lungs in 1691(Ruysch,1691 as cited in Shapiro SD,2010). Over the next centuries, work of Matthew Baillie, Laennec and Gough helped in describing the pathologic enlargement of airspaces and classified it between centriacinar emphysema and panacinar emphysema(Baillie,1799,1808,Gough,1952;Laennec,1835 as cited in Shapiro SD,2010). Various "hypothesis" were proposed over the years to describe the disease pathogenesis:


COPD has been described and subclassified on various clinical, etiopathogenetic and pathological basis. Chronic bronchitis has been associated with a "blue bloater" clinical phenotype on basis of the concept that altered airway anatomy would lead to heterogeneity of airflow distribution within the lung, resulting in ventilation-perfusion imbalance, hypoxemia, and right heart failure. On the other hand, emphysema has been described with the "pink puffer" phenotype based on the concept that it primarily causes decreased airflow from the obstruction and less prominent hypoxia.

Pathologic studies delineate inflammation of airway structures (bronchitis) from destruction of the alveolar wall (emphysema). Emphysema has been described as centriacinar, panacinar and paraseptal based on the location of emphysematous airspaces in an acinus. Centriacinar variety is common in cigarette smokers and panacinar emphysema is predominant in proteinase inhibitor deficiency.
