A system of practical medicine. By American authors. Vol. 3

by Unknown

As an important preface to the subjects considered in this article we introduce an account of the vascular supply of the lungs.

Before entering into a statement of the distribution of the minute vessels to the lungs it is desirable, in view of the possible diseased connections between the larger bronchial and vascular trunks, to recall some points of the topographical anatomy of the latter. "The root of the left lung passes below the arch of the aorta and in front of the descending aorta. The bronchus, together with the bronchial arteries and veins, the lymphatics and lymphatic glands, is placed on a plane posterior to the great blood-vessels. The pulmonary artery lies more forward than the bronchus, and to a great extent conceals it, while the pulmonary veins are placed still farther in advance." The left bronchus "in passing obliquely beneath the arch of the aorta is depressed below the level of the pulmonary artery, which is the highest vessel."¹⁹ Practically, the chances of abnormal communications lie in the relations of the aorta, more especially the different parts of the arch, to the left bronchus and pulmonary artery, and to the trachea, of the innominate artery to the trachea, and of the glandular structures at the root of lung to the pulmonary artery.

¹⁹ Quain's Anatomy, vol. ii. pp. 897, 898.

The encroachment of aneurism of the subclavian artery on the lung, and consequent communication between it and the bronchus, is another form of accidental or extraneous hæmoptysis.

A recognized classification of the vascular systems of the lungs is into—1st, functional; 2d, nutritive. To the first belong the pulmonary arteries and veins, and to the second the bronchial arteries and veins. Both physiological and pathological experience justifies this division.

Notwithstanding the great attention and labor bestowed upon the circulation of the lungs, there are still unsettled some important points. We adopt from Küttner²⁰ some of the anatomical data applicable to our subject. The branches of the pulmonary artery follow uninterruptedly the bronchial ramifications. The mutual relations of the artery and bronchus are such that the larger vessel lying in any preparation of the lung directly next to the bronchus, and running in the same direction, can be pronounced to be a branch of the pulmonary artery. In the lungs of the embryo both lie in the same connective-tissue sheath that originates at the root of the lung, enters with them into the root of each lobule, and there spreads out. In the lobules both run not only closely alongside of each other; there appear also branches of the pulmonary artery on the bronchus itself, and press on to the mucosa of the same.

²⁰ "Beiträge zur Kentniss der Kreislaups-verhältnisse der Saugethierlunge," Virchow's Archiv, vol. lxxiii. p. 476, etc.

With the appearance of the terminal bronchiole this relation is changed. The bronchial artery, as such, ceases; the pulmonary artery—or rather its lateral branches—exclusively surround the alveolar diverticulæ on their external surfaces. At the point where the terminal bronchiole is developed into the infundibula the corresponding trunk of the pulmonary artery divides into a number of branches—"pinselförmig;" each infundibulum receives its stem, which spreads itself after the manner of a feather on its external surface. The terminal branches of the pulmonary artery cover the terminal alveoli. On every lung in which the infundibula and lobules are well distributed the terminal branches of the pulmonary artery extend beyond the borders of the infundibula and lobules into the interlobular and subpleural connective tissue, and here either lose themselves in a capillary distribution or extend to the periphery of an adjoining acinus, being lost in its capillaries.

One peculiarity of the pulmonary artery is that from a large trunk relatively fine lateral branches come. From a vessel of 0.136 mm. come branches of 0.033, 0.016, 0.011, 0.010 mm. The finest disappear immediately as vasa vasorum; the larger pass to the perivascular or peribronchial connective tissue and become capillary, or they appear on the surface of the immediately adjoining lobules and disappear in the capillary paths of the alveoli.

The terminal branches of one and the same principal artery behave differently according as they are distributed to the connective tissue or to the alveoli. In the first case they form wide meshes and narrow tubes, and are not different from the capillary terminations of the body in general. In the other case the meshes are narrow; the vessels in all of the pulmonary capillaries are wide. If these vessels are followed from their origin to their final termination, it will be seen that a considerable part of the pulmonary artery is spread in the interlobular connective tissue; that it is not exclusively a secretory vessel; that the capillary network of all the lobuli are in anastomotic connection.