Emphysema is a form of chronic obstructive pulmonary disease, or COPD, which occurs when there is damage to the alveoili air sacs in the lungs, MedlinePlus says. The air sacs are usually deformed and do not inflate like those in healthy lungs.

Emphysema is part of the process of deteriorating chronic obstructive pulmonary disease, report doctors at the Mayo Clinic. When the air sacs at the end of the bronchioles, or air passages, become damaged, emphysema occurs.