Bronchial Dynamism

THE BRONCHI ARE not simply “air passages” or air conduits. They possess anatomic and physiologic characteristics destined to fulfill a much more important function than that of mere air-distributing channels. But these vital characteristics must not be sought in the bronchial cast, for not even traces of them are to be found in the cadaver, and many of them are not even detected by direct bronchoscopic examination. They are probably best demonstrated by roentgenography after the introduction of a contrast medium, but a single picture taken after the opacification of the bronchial tree is not sufficient to afford a definite knowledge of its functional mechanism. It is necessary to introduce the opaque medium under fluoroscopic guidance, to instruct the patient as to inspiration, expiration, and coughing, and to obtain multiple views—serial and spot films—during the various respiratory processes. It is only thus that the complicated dynamic functions fulfilled by the bronchi may be learned; and upon this physiopathologic basis we may build up a theory of the pathogenesis of the respiratory syndromes.

This method of radiologic investigation allows us to determine the anatomicophysiological characteristics of the normal bronchus. These characteristics are indicated chiefly by: (1) the rhythm and manner of filling; (2) the variations of caliber and static and dynamic sphincteric alterations; (3) the results of pharmacodynamic tests.

Rhythm and Manner of Filling: Fluoroscopically, one observes, while injecting iodized oil into the air tubes, that without question the opaque medium flows into the trachea and into the major bronchi (right and left stem) by the action of gravity. Recumbency has a decisive effect on the route followed by the oil in these major tubes, whereas the influence of the respiratory movements is nil. These facts hold true so long as the quantity of opaque medium is not sufficient to obstruct the tracheobronchial space, for in the latter event the flow is influenced also by the thrust of the column of air that seeks to force its way into or out of the lung.

When the opaque medium reaches the first subdivisions of the main bronchi, that is, the secondary or lobar bronchi, it is noticed that the flow is not progressively continuous as when under the influence of a constant force of invariable magnitude, but that it is pulsating and rhythmic with the respiration. Fluoroscopically this difference between the progressive, continuous flow in the large bronchus and the progressive rhythmical flow in the lobar branches is clearly manifest.

When the opaque medium reaches the branches of still smaller caliber—the bronchioles— its progress is slow and is limited to the inspiratory phase. The flow now shows a forward and backward movement, the oil advancing during inspiration and partially receding during expiration.