Chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis and emphysema, affects more than 16 million Americans, is the fourth leading cause of death in the USA, and costs the nation billions in direct and indirect health care costs. Though only about two million of the 16 million people with COPD have emphysema, emphysema is more disabling, accounting for approximately half of the 114 million days of restricted activity and half of the 53 million days of disability attributed to COPD per year. Emphysema is characterized by destruction of the air space walls, leading anatomically to abnormal, persistent enlargement of the airspaces distal to the terminal bronchioles, and without obvious fibrosis. The clinical result is continuous dyspnea due to hyperinflation of the lung, over distention of the chest wall, disadvantaged respiratory muscles, and hypoxia, even at rest.