Overview of chronic obstructive pulmonary disease (COPD)

COPD is a respiratory disorder characterized by chronic airflow obstruction which encompasses both emphysema and chronic bronchitis, which share similar etiologic factors and often occur together.

COPD is currently the sixth leading cause of death worldwide, and the fourth leading cause of death in the United States, where it affects over 16 million people. The most significant environmental risk factor for the development of COPD is cigarette smoking.

Chronic exposure to cigarette smoke is thought to trigger an inflammatory response within the airways recruiting immune cells to the alveoli. Immune cells release proteases which damage the elastic components of the lung’s extracellular matrix (ECM) causing cell death, sagging, and expansion of individual alveoli into the larger contiguous air spaces. Loss of alveolar surface area reduces alveolar gas exchange, while loss of elasticity reduces the elastic recoil that assists expiration, both factors contributing to the sensations of breathlessness, typical of this condition.

Smoking has also been linked to an increase in the size and number of mucus-secreting goblet cells in the large and small airways, as well as the disruption of mucociliary clearance. These cellular changes lead to excessive mucus production, which narrows the airways and must be cleared by cough, fulfilling the clinical definition of chronic bronchitis. The initial manifestations of COPD are cough, sputum production, and shortness of breath during exercise, especially when involving the arms.