emphysema

Healthy lungs hold millions of tiny grape-like air sacs that recoil like little balloons to push air out. In emphysema, the thin walls between these sacs break down, so clusters of small sacs merge into fewer, larger, floppy spaces. The lung loses its springiness, and air that came in easily now lingers, hard to exhale.

Pathologically, emphysema is permanent enlargement of the airspaces distal to the terminal bronchioles, with destruction of their walls and loss of elastic recoil and surface area for gas exchange. The lost recoil also means the small airways collapse during exhalation, trapping air. It is a major component of COPD and usually results from cigarette smoke, which tips the lung's protease–antiprotease balance toward tissue breakdown.

Because both the elastic 'pull' that keeps small airways open and the alveolar surface for oxygen transfer are reduced, people experience progressive breathlessness and a falling DLCO (gas-transfer measurement). The destruction is not reversible, but stopping smoking, inhalers, oxygen when needed, and rehabilitation can slow progression and improve function; in selected cases, lung volume reduction or transplantation is considered.