Ciliary Streaming in the Lower Respiratory Tract

¹ From the Research Laboratory, St. Luke's Hospital, Duluth, Minnesota

Ciliary streaming in the bronchial tree follows a definite system. Flow begins at the level of the respiratory bronchioles in a very wide stream-bed (meters in total width). The stream-bed narrows rapidly until, when the trachea is reached, it is only some 50 mm in width. A continuously increasing volume of mucus, furnished by the glands throughout the bronchial tree, is added to the stream as it flows toward the larynx. With the stream-bed becoming progressively and sharply narrower, this means that the depth of the mucous blanket or the velocity of flow must increase greatly. En route from the periphery toward the larynx, many obstructions are encountered in the form of tributary bronchial openings. At such obstructions, the mucous blanket passes to the margin of the opening and then divides into two parts that flow in almost opposite directions around the bronchial openings. The direction of ciliary beat changes where bronchial openings are encountered. Sometimes retardation of flow or actual stasis occurs in the center of the lip where division takes place. This may take the form of a whirlpool. Where several bronchi join very close together, the ciliary stream-bed may be reduced to a few millimeters. Islands of cells devoid of cilia occur in the tracheobronchial tree.