Emphysema and chronic bronchitis are airflow-limited states contained within the disease state known as chronic obstructive pulmonary disease (COPD). Emphysema is pathologically defined as an abnormal permanent enlargement of air spaces distal to the terminal bronchioles, accompanied by the destruction of alveolar walls and without obvious fibrosis. Emphysema gradually damages the air sacs (alveoli) in lungs, causing progressively more short of breath. Smoking is the leading cause of emphysema. This syndrome leads to protease-antiprotease imbalance and unopposed action of neutrophil elastases.