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The larynx is a cartilaginous box, triangular in cross-section, with the apex of the triangle directed anteriorly. It is readily felt in the neck and is a landmark for the operation of tracheotomy. We are concerned endoscopically with four of its cartilaginous structures: the epiglottis, the two arytenoid cartilages, and the cricoid cartilage. The epiglottis, the first landmark in direct laryngoscopy, is a leaf-like projection springing from the anterointernal surface of the larynx and having for its function the directing of the bolus of food into the pyriform sinuses. It does not close the larynx in the trap-door manner formerly taught; a fact easily demonstrated by the simple insertion of the direct laryngoscope and further demonstrated by the absence of dysphagia when the epiglottis is surgically removed, or is destroyed by ulceration. Closure of the larynx is accomplished by the approximation of the ventricular bands, arytenoids and aryepiglottic folds, the latter having a sphincter-like action, and by the raising and tilting of the larynx. The arytenoids form the upper posterior boundary of the larynx and our particular interest in them is directed toward their motility, for the rotation of the arytenoids at the cricoarytenoid articulations determines the movements of the cords and the production of voice. Approximation of the arytenoids is a part of the mechanism of closure of the larynx.

The cricoid cartilage was regarded by esophagoscopists as the chief obstruction encountered on the introduction of the esophagoscope. As shown by the author, it is the cricopharyngeal fold, and the inconceivably powerful pull of the cricopharyngeal muscle on the cricoid cartilage, that causes the difficulty. The cricoid is pulled so powerfully back against the cervical spine, that it is hard to believe that this muscles is inserted into the median raphe and not into the spine itself (Fig. 68).

The ventricular bands or false vocal cords vicariously phonate in the absence of the true cords, and assist in the protective function of the larynx. They form the floor of the ventricles of the larynx, which are recesses on either side, between the false and true cords, and contain numerous mucous glands the secretion from which lubricates the cords. The ventricles are not visible by mirror laryngoscopy, but are readily exposed in their depths by lifting the respective ventricular bands with the tip of the laryngoscope. The vocal cords, which appear white, flat, and ribbon-like in the mirror, when viewed directly assume a reddish color, and reveal their true shelf-like formation. In the subglottic area the tissues are vascular, and, in children especially, they are prone to swell when traumatized, a fact which should be always in mind to emphasize the importance of gentleness in bronchoscopy, and furthermore, the necessity of avoiding this region in tracheotomy because of the danger of producing chronic laryngeal stenosis by the reaction of these tissues to the presence of the tracheotomic cannula.

The trachea just below its entrance into the thorax deviates slightly to the right, to allow room for the aorta. At the level of the second costal cartilage, the third in children, it bifurcates into the right and left main bronchi. Posteriorly the bifurcation corresponds to about the fourth or fifth thoracic vertebra, the trachea being elastic, and displaced by various movements. The endoscopic appearance of the trachea is that of a tube flattened on its posterior wall. In two locations it normally often assumes a more or less oval outline; in the cervical region, due to pressure of the thyroid gland; and in the intrathoracic portion just above the bifurcation where it is crossed by the aorta. This latter flattening is rhythmically increased with each pulsation. Under pathological conditions, the tracheal outline may be variously altered, even to obliteration of the lumen. The mucosa of the trachea and bronchi is moist and glistening, whitish in circular ridges corresponding to the cartilaginous rings, and reddish in the intervening grooves.

The right bronchus is shorter, wider, and more nearly vertical than its fellow of the opposite side, and is practically the continuation of the trachea, while the left bronchus might be considered as a branch. The deviation of the right main bronchus is about 25 degrees, and its length unbranched in the adult is about 2.5 cm. The deviation of the left main bronchus is about 75 degrees and its adult length is about 5 cm. The right bronchus considered as a stem, may be said to give off three branches, the epiarterial, upper- or superior-lobe bronchus; the middle-lobe bronchus; and the continuation downward, called the lower- or inferior-lobe bronchus, which gives off dorsal, ventral and lateral branches. The left main bronchus gives off first the upper-or superior-lobe bronchus, the continuation being the lower-or inferior-lobe bronchus, consisting of a stem with dorsal, ventral and lateral branches.

[FIG. 44.—Tracheo-bronchial tree. LM, Left main bronchus; SL, superior lobe bronchus; ML, middle lobe bronchus; IL, inferior lobe bronchus.]

The septum between the right and left main bronchi, termed the carina, is situated to the left of the midtracheal line. It is recognized endoscopically as a short, shining ridge running sagitally, or, as the patient lies in the recumbent position, we speak of it as being vertical. On either side are seen the openings of the right and left main bronchi. In Fig. 44, it will be seen that the lower border of the carina is on a level with the upper portion of the orifice of the right superior-lobe bronchus; with the carina as a landmark and by displacing with the bronchoscope the lateral wall of the right main bronchus, a second, smaller, vertical spur appears, and a view of the orifice of the right upper-lobe bronchus is obtained, though a lumen image cannot be presented. On passing down the right stem bronchus (patient recumbent) a horizontal partition or spur is found with the lumen of the middle-lobe bronchus extending toward the ventral surface of the body. All below this opening of the right middle-lobe bronchus constitutes the lower-lobe bronchus and its branches.

[FIG. 45.—Bronchoscopic views. S; Superior lobe bronchus; SL, superior lobe bronchus; I, inferior lobe bronchus; M, middle lobe bronchus.]

[56] Coming back to the carina and passing down the left bronchus, the relatively great distance from the carina to the upper-lobe bronchus is noted. The spur dividing the orifices of the left upper- and lower-lobe bronchi is oblique in direction, and it is possible to see more of the lumen of the left upper-lobe bronchus than of its homologue on the right. Below this are seen the lower-lobe bronchus and its divisions (Fig. 45).

Dimensions of the Trachea and Bronchi.—It will be noted that the bronchi divide monopodially, not dichotomously. While the lumina of the individual bronchi diminish as the bronchi divide, the sum of the areas shows a progressive increase in total tubular area of cross-section. Thus, the sum of the areas of cross-section of the two main bronchi, right and left, is greater than the area of cross section of the trachea. This follows the well known dynamic law. The relative increase in surface as the tubes branch and diminish in size increases the friction of the passing air, so that an actual increase in area of cross section is necessary, to avoid increasing resistance to the passage of air.

The cadaveric dimensions of the tracheobronchial tree may be

epitomized approximately as follows:

Adult

Male Female Child Infant

Diameter trachea, 14 X 20 12 X 16 8 X 10 6 X 7

Length trachea, cm. 12.0 10.0 6.0 4.0

Length right bronchus 2.5 2.5 2.0 1.5

Length left bronchus 5.0 5.0 3.0 2.5

Length upper teeth to trachea 15.0 23.0 10.0 9.0

Length total to secondary bronchus 32.0 28.0 19.0 15.0

In considering the foregoing table it is to be remembered that in life muscle tonus varies the lumen and on the whole renders it smaller. In the selection of tubes it must be remembered that the full diameter of the trachea is not available on account of the glottic aperture which in the adult is a triangle measuring approximately 12 X 22 X 22 mm. and permitting the passage of a tube not over 10 mm. in diameter without risk of injury. Furthermore a tube which filled the trachea would be too large to enter either main bronchus.

The normal movements of the trachea and bronchi are respiratory, pulsatory, bechic, and deglutitory. The two former are rhythmic while the two latter are intermittently noted during bronchoscopy. It is readily observed that the bronchi elongate and expand during inspiration while during expiration they shorten and contract. The bronchoscopist must learn to work in spite of the fact that the bronchi dilate, contract, elongate, shorten, kink, and are dinged and pushed this way and that. It is this resiliency and movability that make bronchoscopy possible. The inspiratory enlargement of lumen opens up the forceps spaces, and the facile bronchoscopist avails himself of the opportunity to seize the foreign body.