COPD (chronic obstructive pulmonary disease) refers to a group of diseases, primarily bronchitis and emphysema. Bronchitis is a chronic inflammation of the bronchi caused by irritants such as cigarette smoke, air pollution, or infections. The inflammation results in swelling of the mucous membrane lining the bronchi, increased mucus production, and decreased movement of mucus by cilia. Emphysema usually follows bronchitis and involves the destruction of the alveolar walls. Ultimately, the lungs lose their elasticity and become less efficient.