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

by Unknown

Passive congestion may be occasioned by a retardation of the blood-flow from the lungs; as, for example, by a hindrance to its onward passage through the left chambers of the heart in consequence of obstructive valvular disease, especially a great degree of mitral or aortic stenosis. So also mitral or aortic incompetency, by allowing the blood to be crowded backward in the pulmonary veins, may interfere with its passage through the lungs, and in this way set up passive hyperæmia.

By some writers mere weakness of the heart is spoken of as a cause of passive congestion of the lungs; but it can hardly be regarded as such apart from influences affecting the blood itself or the tonicity of the pulmonary vessels; for it is to be considered that while weakness of the left chambers of the heart might impede the onward course of the blood received from the lungs, yet at the same time the right chambers, if weakened in a corresponding degree, would send less blood into those organs, and then the conditions of passive hyperæmia would not exist. It is well known, moreover, that cardiac weakness coming on suddenly as in syncope, or gradually as in various asthenic diseases, may be present without the occurrence of any signs of pulmonary congestion. Yet it is not impossible that there may be a disturbance of the balance between the actions of the right and left sides of the heart, and that thus passive congestion of the lungs may result from a relatively greater weakness on the left than on the right side of the heart, so that the left auricle and the pulmonary veins may be obstructed, and backward pressure produced while the right ventricle is still sending blood into the lungs.

It is probable, however, that, in addition to the propulsive power exercised on the blood by the contraction of the heart, another agency affecting its passage through the lungs is the interchange of gases in respiration; and therefore any interference with the reception of oxygen and the elimination of carbonic dioxide may tend to retard the blood-flow, and thus favor stasis or passive congestion. In this way the inhalation of impure air, especially air containing an undue amount of carbonic dioxide, may occasion passive hyperæmia.

Pulmonary oedema is never a primary affection, but is always due to some preceding disease. In the first place, it may, as already stated, take its origin directly from congestion of the lungs, the walls of the obstructed vessels allowing the transudation of serum, which will collect in the air-cells and connective tissue and also in the mucous membrane of the terminal bronchi. In an early stage it may be present in the walls only of the alveoli without being effused into their cavities.

Another cause of pulmonary oedema is obstruction of the circulation of a part of a lung, such as may take place in pneumonia or miliary tuberculosis, the vessels of other parts becoming distended by backward pressure, so that the serum of the blood will exude into the air-cells or interstitial tissue. When this occurs in pneumonia it may be a most alarming and dangerous complication.

Still another and very frequent cause of pulmonary oedema is Bright's disease in its different forms, in which the oedema occurs as a part of the general dropsy incident to these affections. In acute congestive nephritis it may come on very rapidly, constituting acute pulmonary oedema. Hertz remarks that an acute oedema may take place in the course of an acute nephritis, as has been reported by Lebert, but that such an occurrence is not frequent.¹ The writer of this article has himself seen several cases of acute pulmonary oedema occurring as a part of the dropsy of scarlet fever.

¹ Ziemssen's Cyclop., v. p. 279.

More frequently it is met with in chronic albuminuria, and varies in amount from time to time, as dropsical effusions elsewhere do in this condition.

Attacks of asthmatic dyspnoea are not uncommon in the course of Bright's disease, especially in cases of chronic contracted kidney. They are described as uræmic asthma, and are referred by some writers to the action of the depraved blood on the centres of respiration. This explanation may be correct in some cases, but it seems likely that they are due in part to dropsical oedema of the bronchial mucous membrane, the connective tissue, or the air-cells. A weakened condition of the heart, such as is apt to occur in advanced periods of Bright's disease, has probably some share in determining the oedema.

In any case of oedema, according to its situation, whether it is in the connective tissue, the bronchial mucous membrane, or the air-cells, and according also to the amount in which it is effused, it will interfere more or less with breathing. If there be interstitial infiltration with swelling of the bronchial mucous membrane, lessening the calibre of the tubes, there may be merely some embarrassment of respiration; but if the effusion invade any considerable number of the air-cells, urgent dyspnoea will be produced. Oedema is generally most abundant at the lower part of the lungs, and is not uncommonly associated with pleural effusion, the two conditions being due to the same cause; and then the interference with respiration is greater and more perilous.