Emphysema is a common type of COPD or Chronic Obstructive Pulmonary Disease. In the lungs of a patient with emphysema, the tiny air sacs (alveoli) are damaged. Like old balloons, they get overstretched and over time become unable to express all of the air back out. This causes air to get trapped in the air sacs which causes irreversible damage. The most common cause of emphysema is cigarette smoking.

Emphysema is a long-term, progressive disease of the lung that primarily causes shortness of breath. In people with emphysema, the lung tissues necessary to support the physical shape and function of the lung are destroyed. It is included in a group of diseases called chronic obstructive pulmonary disease or COPD (pulmonary refers to the lungs). Emphysema is called an obstructive lung disease because the destruction of lung tissue around smaller airways, called alveoli, makes these airways unable to hold their functional shape upon exhalation. 

The primary cause of emphysema is cigarette smoking. In some cases, it may be due to alpha 1-antitrypsin deficiency. Severe cases of A1AD may also develop cirrhosis of the liver, where the accumulated A1AT leads to a fibrotic reaction.