From [Greek: hydôr], water, and [Greek: thôrax], the chest.
DEFINITION.—Dropsy of the chest. The accumulated fluid in the pleural cavity which resembles the serum of the blood is not the product of inflammation, but is caused by mechanical obstruction to the circulation or by blood-poisoning. Hydrothorax is never idiopathic, but invariably secondary, resulting from disease, not of the pleura, but of the circulatory system or of the blood itself.
HISTORY.—Before pathological anatomy had been accurately studied, effusions resulting from inflammatory processes in the pleura were confounded with simple hydrothorax, which is not a variety of pleurisy. Royer217 and Laennec218 divided hydrothorax into idiopathic and symptomatic; Darwell219 adopted in a great measure their views. They did not draw the distinction between the passive transudation of serum, constituting the condition known as hydrothorax, and exudations resulting from idiopathic pleurisy. Before physical modes of exploring the chest were used there was great uncertainty in the diagnosis of collections of fluid in the pleural cavity.
217 Dict. de Méd., 1832.
218 Dis. of Chest, Forbes's edition.
219 Cyc. Pract. Med.
ETIOLOGY.—Dropsical effusion in the thorax is produced by the same causes which give rise to collections of watery fluid in other serous cavities and in the connective tissue, constituting general anasarca. Primary among the causes is obstruction of the venous circulation in the walls of the chest or in the lungs. Mitral disease, especially insufficiency with dilatation, deranges the normal circulation in the lung and its serous coverings, producing hyperæmia, oedema of the lung, and finally serous effusions into the pleural sac. General dropsy results. According to Fernet,220 in dropsies resulting from mitral disease oedema of the lungs and hydrothorax always precede all other oedemas. Fraentzel,221 on the contrary, states that it does not occur until there is no longer any room for the transuded fluid in the deeper portions of the subcutaneous tissues. Other diseases of the heart produce hydrothorax. Whenever there is abnormally high venous pressure, which invariably follows dilatation of the right side after compensatory hypertrophy has reached its limit, and the heart literally yields to the backed current of blood, we must expect dropsical results. Intra-thoracic tumors, aneurisms, emphysema, and sclerosis of the lung cause hydrothorax by pressing upon the venous trunks and upon the thoracic duct without producing general dropsy. Chronic diseases, such as cancerous disease, chronic malaria, etc., produce great exhaustion and give rise to general hydræmia. Especially is this the case in chronic disease of the kidneys, such as the several varieties of nephritis and amyloid degeneration, where there has been a loss of albumen for a long time and the blood-serum has been rendered poorer in solid constituents. Hydrothorax is not a disease, but a symptom resulting from a variety of causes which produce physical exosmosis of the serum of the blood.
220 Nouveau Dict. Méd., vol. xxviii.
221 Ziemssen's Cyc., Amer. trans., vol. iv.
PATHOLOGICAL ANATOMY.—Hydrothorax being merely dropsy of the thoracic cavity, there is no lesion of the pleura. There is a collection varying from 100 grammes to many liters of fluid in the cavity. It differs from the effusion in subacute pleurisy in its small quantity of fibrin, in having far less of albuminoid material, and no white blood-corpuscles. The water collects almost always in both sides of the chest, more on the side on which the patient lies in bed. In the recumbent position the fluid gravitates posteriorly more than the effusions of pleurisy. In the upright position it will follow Ellis's curved line more regularly than in effusions resulting from pleurisy, for there are no adhesion-bands interfering with its doing so. The fluid is limpid, of a light-yellow or citron color. Its composition resembles that of the plasma of the blood, but it contains more water and less of the constituent elements. Alex. James222 found that the amount of mineral matter was the same in dropsical fluids in all parts of the body, and that the organic albuminoid substances were larger in quantity in the pleura than in any other cavity. The amount of organic substances varied directly in accordance to the degree of pressure on the different capillary vessels. The anatomical changes in the pleura and the subpleural connective tissue are similar to those found in other collections of dropsical fluid. They are swollen and thickened by maceration with water. They become opalescent and less firm of texture. The lungs retract as the fluid increases in quantity. As the filtrates collect in both pleural sacs, the lungs do not forcibly collapse. The patient would sink at once were this the case. The arch-tension of the diaphragm is but rarely overcome, and consequently we must not expect to find the liver and spleen pushed down, especially when there is fluid in the peritoneal cavity. The position of the heart, unless there is a marked difference in the collections of the two sides, is but little altered, the retractive force of both lungs being impaired.