**1. Introduction**

46 Chronic Obstructive Pulmonary Disease – Current Concepts and Practice

[78] Reilly J, Washko G, Pinto-Plata V, et al. Biological lung volume reduction: a new

COPD remains a major public health problem. It is the fourth leading cause of chronic morbidity and mortality in the United States, and is projected to rank fifth in 2020 in burden of disease caused worldwide, according to a study published by the World Bank/World Health Organization. COPD is a preventable and treatable disease, with some significant extra-pulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterized by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and associated with an abnormal inflammatory response of the lung to noxious particles or gases. Smoking remains the major risk factor for this disease, but inhalation of other pollutants and genetic factors also play a role.

Inhalation of cigarette smoke and other pollutants leads to a chronic inflammatory process in the small airways and the lung parenchyma, which includes an influx of macrophages, polymorphonuclear neutrophils (PMN), T lymphocytes (with CD8+ T cells exceeding the numbers of CD4+ T cells), and B lymphocytes (1-4). This inflammatory process over a prolonged period, leads to destruction of the alveolar walls leading to airspace enlargement, loss of lung elasticity, closure of small airways, and irreversible airflow obstruction. Pathological changes also include mucous metaplasia and mucus hyper-secretion. The small airways narrow due to the combined effect of mucus plugging, inflammation in the airways walls and lumen, and subepithelial fibrosis and can become obstructed (1). COPD is a complex disorder with many processes at play but there is strong evidence that proteinases make critical contributions to all the pathologic processes detected in the lungs of COPD patients.
