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

by Unknown

ETIOLOGY.—As catarrhal pneumonia is so closely associated with bronchitis, and so commonly preceded by it, it may be premised that all the causes of bronchial catarrh must be considered as liable to induce this form of pulmonary inflammation, whether they do so by exciting bronchitis, which subsequently extends to the alveoli, or whether, as more rarely happens, they affect simultaneously the lining membrane of the bronchi and of the lobules.

There are, however, several influences which must here be carefully considered, since they have a special tendency to determine the production of the more grave form of disease.

The effect of age in predisposing to catarrhal pneumonia is undoubtedly great, and yet it seems to have been often over-estimated, since by many this has been regarded almost as a disease peculiar to childhood. The great frequency with which young children were formerly held to be affected by this form of pneumonia has, however, been found to be due in part to the fact that many cases of pulmonary collapse were included with it; while, on the other hand, there is strong reason to believe that the frequency with which adults are attacked has been greatly under-estimated in consequence of the failure on the part of the profession at large to clearly recognize this affection. It seems in the highest degree important that more correct views on this subject should be generally received. While it is probable that the more severe and widely-disseminated pneumonias of catarrhal type are commonly recognized now-a-days, it appears undoubted that in very many instances of apparently mild sickness, of acute or subacute character, which are regarded as simple febrile colds or as the result of malaria, the true condition is one of circumscribed catarrhal pneumonia, which, while threatening no immediate danger to life, may if neglected leave lesions of grave significance. Still, it is undoubted that it is during the early years of childhood, and particularly the first five years, that catarrhal pneumonia, and more especially its grave and fatal form, is of frequent occurrence; while the period of next greatest liability is at the other extreme of life, among aged and debilitated subjects.

Under the head of Pathology we shall have occasion to dwell on the relations between defective respiratory power, pulmonary collapse, and catarrhal pneumonia; and it is evident that this connection helps to explain the relative frequency of the latter in early childhood, when conditions of debility are so common, and when rickets not rarely is superadded as an important factor. Another potent cause of the liability of young children to catarrhal pneumonia is the prevalence at that period of life of the infectious diseases, which are apt to be complicated with bronchitis, and which then present a combination of conditions favoring its development. This is especially true of measles, of whooping cough, and of diphtheria, while influenza, which is also frequently complicated with this form of pneumonia, is operative at all ages. Among predisposing causes which operate chiefly at a later period of life must be mentioned organic diseases of the heart and vesicular emphysema. The latter especially has shown itself important in our experience, both as predisposing to the occurrence of catarrhal pneumonia and as adding to the gravity of the attack.

Unquestionably, all states of bad nutrition and depressed vitality render the system much more liable to attacks of catarrhal pneumonia. The bad air of crowded houses or of ill-ventilated public institutions, especially if conjoined with the effect of improper food and of other defects of hygiene, plays an important part in inducing the fatal forms of this disease which are common among children exposed to such conditions. It is equally evident that among adults the effect of overwork, with insufficient sleep and outdoor exercise, is to develop a peculiar sensitiveness and weakness of system which make the ordinary causes of bronchitis capable of exciting a deeper and more serious catarrh. Finally, there are many individuals who possess a catarrhal diathesis—that is, in whom the epithelial layers are especially vulnerable, and when attacked are especially prone to take on cellular proliferation of a deep-seated and obstinate character. Such constitutions, which are frequently found in the subjects of phthisical heredity, furnish a ready soil for the development of catarrhal pneumonia.

Nor must the practical lesson be here overlooked that when acute or subacute bronchitis exists, an additional motive for prompt and thorough treatment is to be found in the fact that undue fatigue or exposure may be followed by an extension of the inflammation and by the onset of catarrhal pneumonia.

PATHOLOGY AND MORBID ANATOMY.—Allusion has already been made to the relation existing between catarrhal pneumonia and collapse of the lung; and the present seems to be the proper place to speak more fully of it, since in order to appreciate the lesions in any case it is necessary to distinguish between those which are the result of the inflammatory process and those which can be explained by simple collapse of the lung-tissue. It is indeed true that in some cases the development of catarrhal pneumonia takes place in areas already the seat of collapse. This is only what would naturally be expected. For the production of both conditions the existence of preceding bronchial catarrh is, if not necessary, at least highly favorable. The folds of the swollen mucous membrane of the smaller tubes come into contact with each other, or else the diminished lumen of the tubes is occluded by the viscid mucus formed as the result of the catarrh. The normal activity and rhythm of respiration is disturbed by the fever and the lowered innervation. During expiration more and more of the air escapes from the alveoli of the affected area through these partly-obstructed tubes, while during inspiration, owing to the less force of that part of the respiratory act and to the shape of the bronchial tree, air cannot enter to replace it. Thus, or by the action of a plug of mucus in a conical bronchial tube, serving as a ball-valve, a condition of airlessness or of collapse is induced in a more or less extensive area. It is not, indeed, to be supposed that the mere occurrence of such collapse serves in any way to excite inflammation of the alveoli. But at the same time it is evident that there will be a strong likelihood that the catarrh which has advanced so deeply into the finer tubes will extend in some spots to the alveoli, and consequently that in a collapsed area of some extent there will be one or more foci of pneumonia developed. Moreover, it must be remembered that the collapsed lung-tissue becomes more or less hyperæmic and disposed to take on inflammatory action, and that the irritating bronchial secretions, the suction of which into the alveoli plays an important part in these affections, would necessarily be less apt to be dislodged by cough and expectoration from areas which had become collapsed. On the other hand, it is evident that when areas of catarrhal pneumonia have occurred directly from extension or establishment of catarrh in air-containing alveoli, the conditions will exist which favor the development of collapse in the surrounding zones of lung-tissue. Thus it happens that while the lesions either of collapse or of catarrhal pneumonia are found separately, it is common to find more or less evidences of alveolar inflammation in connection with collapse, especially if it has lasted any length of time; and still more common to find a considerable proportion of collapse coexisting with catarrhal pneumonia.

A simple practical rule must therefore be here insisted upon: that in all post-mortem examinations of the lungs in cases of catarrhal pneumonia, after careful study of the external appearances, a moderate inflation by means of a blowpipe must be practised, and the effects of this upon the consolidated areas be carefully studied before the lung be incised, in order that any element of collapse may be recognized and eliminated.

The external appearance of the lungs usually presents evident lesions. There are patches or layers of soft lymph on the pleura over the affected areas, and when the former are removed the serous membrane is found roughened, congested, and ecchymosed. On the other hand, while the pleura over a collapsed patch usually presents small ecchymoses, there is rarely any evidence of inflammation. More or less evident signs of vesicular emphysema are also usually present, bearing some proportion to the extent of the pulmonary collapse. When the areas affected are small and scattered, the emphysema is limited to their neighborhood; but when, for instance, both lower lobes are extremely involved, the upper lobes may present a high degree of emphysematous distension. In rare instances subpleural emphysema, from separation of the membrane over a pneumonic focus, may be observed; and even, as in a case published by me some years ago,¹ perforation of the separated pleura may occur, leading to pneumothorax.

¹ Philada. Med. Times, Aug. 15, 1872, p. 425.