When the lungs' airways are regularly assaulted by a troublesome irritant over a long time, as in cigarette smoking, they eventually respond in two ways. They become permanently inflamed, with fluid swelling the tissue that lines the airways. Since this narrows the airways, airflow resistance increases. The lungs also radically increase mucus production in a powerhouse attempt to clean out this irritant. In a two-pronged effort, the mucus glands grow several times their normal size and the goblet cells both become far more numerous and spread out to populate even the smallest airways.

In this early stage of chronic bronchitis, the excessive sputum does not yet block the patient's airways because the cough is still strong enough to move a great deal of it out of the lungs. Because this mucus is not permitted to stagnate in the airways, it has not yet become a hospitable site for bacterial growth. The impressive sputum reservoir that the lungs produce is still nonpurulent, a medical term meaning "without bacterial content." The airways are still sterile.

But gradual paralysis of the ciliathe tiny hair-like structures responsible for moving mucus up and out of the airwayspermits mucus to accumulate in smaller airways. Then air can no