In emphysema (from the Greek word for "inflation"), the walls of the alveoli (air sacs) in the lung are destroyed and lose elasticity (the ability to spring back to shape), hindering the outflow of air (from the sacs) when a person exhales. Emphysema frequently occurs together with chronic bronchitis, and together these two diseases are called chronic obstructive pulmonary disease (COPD).

Emphysema is characterized by loss of the normal elasticity of the lung that helps to hold airways open....