Cigarette Smoke and the Physiologic Drainage of the Bronchial Tree

¹ The Research Laboratory, St. Luke's Hospital, Duluth 11, Minnesota.

1. Inhaled cigarette smoke by-passes the natural cleansing mechanism of the nose, to which most air pollutants are subjected. The tar droplets from the smoke are diffusely deposited in the mucous blanket throughout the tracheobronchial tree as the inspired air flows down. These deposits are somewhat heavier just under the vocal cords and in the root of the lungs than elsewhere. The greatest total quantity is deposited in the small bronchioles and alveoli.

2. The physiologic drainage of the bronchial tree is accomplished by the mucous blanket, which, motivated by the underlying cilia, constitutes the diary stream. From respiratory bronchioles to esophagus, the streambed narrows markedly and probably the velocity of flow of mucus increases as the stream-bed narrows. In its ever-narrowing course from respiratory bronchioles to esophagus, the ciliary stream encounters a number of naturally-occurring obstructions in the form of squamous islands, bronchial openings, and the squamous epithelium of the vocal cords. Retardation of the ciliary stream may occur at these areas and may be further enhanced in the presence of cigarette smoke, which slows or temporarily stops ciliary action. Thus, prolonged action of any carcinogen contained in the ciliary stream could occur at these spots.

3. The distribution of squamous-cell carcinoma in the respiratory tract suggests a relation to the ciliary streaming.