These names designate conditions in which the lung alveoli and finer bronchi contain no air, but are in a condition similar to that of the fœtal lung before inflation, the internal surfaces of the alveoli being applied to each other. It may be a survival of the foetal state, or it may be subsequently produced by the alveoli being, in some way, emptied of their air.

Atelectasis

In its strict sense this term is applied to an imperfect expansion of the lung at birth. It is frequently found in new-born children, being, indeed, a survival of the foetal state. The lungs have to a greater or less extent remained uninflated. The non-inflation may be due to some obstruction in the bronchi, by meconium or mucus, but in most cases it is merely due to the weakness of the inspiratory efforts. The new-born child usually cries lustily, and in the deep inspiratory gasps between the cries the lungs are fully inflated. But if the child be weak or has not cried freely, certain parts of the lungs are apt to remain devoid of air. The atelectasis of the new-born is most frequent in the lower lobe, and in the posterior parti of this lobe.

It may be only in small areas in the midst of the inflated lung tissue, or the greater part of a lobe, or the whole lobe may be affected. In any case the non-inflated part usually shows by its shape that it is the district supplied by one or more bronchi.

The atelectasis shows itself by the smaller volume of the part. If it is in the midst of inflated lung it is depressed below the surface. Like the foetal lung, it is redder than the normal, firmer to the touch, and non-crepitant when handled. It is important to distinguish this condition from condensation of the lung, for which it is liable to be mistaken. In both conditions the lung is devoid of air, but in the case of condensation it is so because the air spaces are filled up with solid material, usually inflammatory exudation.

There is no doubt that a lung which was partly atelectatic immediately after birth may subsequently become perfectly inflated. On the other hand, there is reason to believe that, if the atelectasis persist long, the lung becomes incapable of inflation. If the child survive, the applied walls of the lung alveoli adhere and an actual obliteration of the latter occurs. The part gradually atrophies, and it has been supposed that cicatrices sometimes seen in the adult lung and without any obvious cause may have this origin.

Bronchiectasis occurs in consequence of the atelectasis, the bronchi dilating to fill up the space left by the non-inflation, so that the bronchiectasis is complementary (see Fig. 354). In a case observed by the author, and referred to further on under Hypertrophy of the Lung, the greater part of one lung had failed to inflate, and the bronchial tubes were dilated into considerable sacs.

The question arises here whether, after inflation of the lung, portions or the whole may again collapse. We shall see immediately that collapse occurs in the adult, and there is no reason to suppose that it does not occur in the new-born infant. There are undoubted cases of children who have lived over twenty-four hours and have cried, in whose bodies the lungs have been found with only an island here and there of inflated lung.

Collapse Of The Lung Or Apneumatosis

This is an emptying of the lung of air at any time after its expansion. In some cases it is due to direct Compression of the lung the air is simply squeezed out of it. Usually this arises from the presence of fluid or air in the pleural cavity. In that case the air vesicles may be only partly emptied and may readily recover. But if the exudation is great and remains long, then the lung may be pressed upwards and backwards and come to form merely a red fleshy layer flattened against the chest wall. This condition is often called Camification, and in it the tissue appears darkly pigmented, the absence of blood and the packing together of the lung tissue exaggerating the existing carbonaceous pigmentation. The cause mentioned above is by far the most frequent in producing collapse by pressure, but there are others. Curvature of the spine sometimes causes such a narrowing of a part of the chest that the lung is squeezed or collapsed. Aneurysms or tumours may also compress the lung, but they more frequently cause collapse by obstructing the bronchi. Even distension of the abdomen, by pressing the diaphragm upwards and limiting the chest space, may cause a partial collapse. A great distension of the pericardium may have a similar effect.

A very important cause of collapse is Obstruction of bronchi. A limited collapse is exceedingly frequent in bronchitis, especially in children. The collapse very often appears in the form of small wedge-shaped depressions at the edges of the lungs, and may be almost concealed by neighbouring emphysematous lung. But sometimes, especially in children, the collapse may be much more extensive.

One mode in which this collapse occurs has been described by Gairdner. If a pellet of mucus obstructs a bronchus it may act to a certain extent like a ball valve; it is pushed out into the larger tube during expiration, and being drawn back against the bifurcation in inspiration stops the tube. In this way the escape of air during expiration is allowed, but the entrance of air during inspiration prevented. The respiratory movement will, thus act, to a certain extent, like an air pump, and the portion of lung tissue concerned will be gradually emptied of air.

Another way in which collapse probably occurs when a bronchus is obstructed has been demonstrated by Lichtheim. It is to be remembered that the lung tissue is elastic, and that left to themselves the alveoli collapse and their walls apply themselves together. If a bronchus be obstructed, and communication with the external air withdrawn, the elasticity of the lung tissue will cause pressure to be exercised on the air contained in the alveoli, and absorption of its gases will be thus promoted. It has been proved that such absorption actually occurs somewhat rapidly, first of the oxygen, then of the carbonic acid, the nitrogen being slowest of absorption. The lung of course collapses as the air is absorbed.

It has just been stated that collapse from bronchial obstruction is most common in the bronchitis of children, but it is necessary to observe that in children, in whom the form called capillary bronchitis is common, this disease is often accompanied by a condition which is apt to be mistaken for collapse, namely, lobular condensation. The inflammatory process in the bronchi readily passes in children to the lung alveoli, and the products fill these up, causing condensation of a portion of the tissue which has a wedge-shaped configuration similar to that of the collapsed portion. Of course, these two conditions may co-exist in the same lung, or we may even have a combination of them, the collapsed lung becoming the seat of inflammation, and so passing into the condition of condensation.

Literature

Heller, D. Arch. f. klin. Med., xxxvi.; Coats, Trans, of Clin. Soc. of Lond., 1884; Gairdner, On bronchitis, 1850; Ltchihkim, Arch. f. exper. Path., 1879.