Emphysema is a disease of the lungs characterized by destruction of small air sacs (alveoli), where the exchange of oxygen into and carbon dioxide out of the bloodstream occurs. As the walls of the alveoli break down, enlarged airspaces known as bullae are formed within the lung. In addition, the alveolar walls no longer act to hold the small airways (bronchial tubes) open. This leads to obstruction of airflow from the lungs as the patient exhales, resulting in shortness of breath and exercise intolerance in patients. Bulla formation and obstruction to airflow result in overinflation of the lungs until the patient's chest takes on a barrel-shaped appearance. Because bronchitis (inflammation of the airways) often coexists with emphysema, obstruction to airflow may be further compounded by a swelling of the membrane lining the airways.
Destruction of the alveoli also results in a reduction of the surface area available for gas exchange. If emphysema is severe enough, elevated carbon dioxide and reduced oxygen levels in the bloodstream are noted.
Shortness of breath is the outstanding symptom reported by individuals suffering from this disorder, and the disease often progresses until the patient is incapable of the slightest exertion. Death may eventually result from accompanying infections, respiratory failure, or cardiac complications due to low oxygen levels.
The exact cause of emphysema remains unknown. Cigarette smoking is closely associated with disease accounting for most cases. Industrial pollution may play a role. In a small number of cases a genetic link is suspected. These individuals with emphysema lack a gene that controls the liver production of a protein called alpha-1-antitrypsin (AAT). AAT normally blocks the function of a molecule called neutrophil elastase, a degrading enzyme, produced by white blood cells. In individuals who lack the AAT blocking protein, neutrophil elastase goes unchecked and eats away at alveolar tissue. Replacement AAT is often given to these individuals via injection, although the success of this treatment remains to be proved.
Progression of emphysema can be retarded by abstinence from smoking, and symptomatic relief can in some cases be provided by drugs that dilate the airways. In later stages the patient requires oxygen at all times. Prompt treatment of infections is vital. Certain types of emphysema may be localized to portions of one or both lungs and can be treated by surgical removal.