PNEUMONOKONIOSIS.
BY EDWARD T. BRUEN, M.D.
DEFINITION.—A generic term applied to pulmonary diseases due to the inhalation of particles of irritating dust.
SYNONYMS AND CLASSIFICATION.—The synonyms and classification of pneumonokoniosis have been based upon the character of the dust inhaled, using such terms as anthracosis ([Greek: anthrax], coal), disease due to coal-dust; siderosis ([Greek: sidêros], iron), due to metallic dust; chalicosis ([Greek: chalix], gravel or pebbles), due to mineral dust; tabacosis, due to tobacco-dust; and byssinosis ([Greek: byssos], cotton), due to cotton fibre and dust. A more imperfect classification has been derived from the avocations of the sufferers; for example, miners' phthisis, Sheffield grinders' rot, potters' consumption and asthma, freestone-hewers', masons', or millers' lung.
HISTORY.—From the early experiments of Cruveilhier, who injected mercury into the system and subsequently noted the pulmonary changes, down to the experiments of the present day, evidence has accumulated to show that inorganic irritant materials are capable of exciting inflammatory new formation in the lungs. The difference between the changes produced in the lungs by experimental processes and those occurring after the inhalation by artisans of inorganic materials consists in degree rather than in essential character. In pneumonokoniosis the pulmonary processes are gradually developed, and consequently the ensuing changes in the tissues represent those usually associated with the more chronic forms of pulmonary lesions, and may not only occasion phthisis, but during years of life may cripple the sufferer by engendering chronic catarrhal processes in the mucous membranes, complicated by emphysema or asthma.
ETIOLOGY.—Predisposing Influences.—Atmospheric dust is composed of organic and inorganic matter, and both have been demonstrated by many admirable experiments to be very widely diffused in the air we breathe. In most instances the injurious action of inorganic dust is augmented by the conditions of imperfect ventilation under which it is inhaled, because the amount of dust deposited in the lungs is thereby increased. Illustrations of this fact can be found in various avocations, particularly among miners. The injurious action of dust inhaled when there is imperfect ventilation is increased in proportion as there is deprivation of sunlight, both conditions tending to lower the vitality of the artisan. Again, the rigor of confinement of parents engenders a sickly or scrofulous constitution which is transmitted to their offspring, causing great mortality among the children of artisans, especially where they, in turn, are subjected to unfavorable environment.
When work is performed in constrained or stooping positions, or when proper inflation of the chest is not secured, the liability to pulmonary disease is increased.
The foregoing conditions having been considered, the injurious action of dust upon the lungs is in proportion to the quantity deposited in them. The entrance of dust is, however, physiologically opposed by the action of the pulmonary cilia, although the resistance is frequently ineffectual. This inefficiency may be owing to the quantity of dust inspired or to deficient tissue-integrity in general upon which the ciliary action depends in inverse ratio.
Exciting Causes.—These vary materially in different avocations. The most injurious industries are those in which the various forms of grindstones are used, or those trades which necessitate labor in an atmosphere loaded with particles of steel, iron, or flint. In London, where millstones are made from French burr, a peculiarly hard flint quarried on the Marne to the east of Paris, and more liable to chip from its hardness and dryness than flint quarried in other places, the mortality among the artisans is said to be very much increased. Peacock, who has investigated this subject, asserts that in certain manufactories of this class the average age of those engaged is very low: of 23 apprentices the average age was twenty-four, and the longest period during which the occupation could be followed was thirteen years. The same author has also demonstrated the presence of silicious particles in the lung-tissues. In the pottery districts of England the death-rate from pulmonary diseases is greater among those who work at that avocation than among the other inhabitants.
The study of the effect upon the lungs of the inhalation of coal-dust is very important. In the coal-mining region of Cornwall the deaths from chest diseases among miners is double that of males in the community at large; the mortality of those working in lead-mines is also very great.
The black spit of pitmen, examined under the microscope, is seen to consist of mucus enclosing finely-divided particles of coal, frequently presenting the special bands of the particular coal in which the subject of the disease may have worked. The fact that coal-dust may enter the lungs in the act of breathing is corroborated by Rindfleisch, who, reporting for Traube a post-mortem made in 1860, found in the fluid expressed from the parenchyma of the lung "one of the dotted cells of coniferous wood entirely carbonized, in which he was able to count seven pores close together. This particle of charcoal-dust equalled half the diameter of an alveolus." Inhaled particles of dust first penetrate the bronchial tubes and infundibula, and, entering the alveolar parenchyma, mix with the general current of extravascular fluid, together with which they ultimately tend to reach the lymphatic vessels. On their way they must occasionally meet with corpuscular elements which have the power of permanently adopting small solid particles into their protoplasm: foremost among such elements are the stellate corpuscles of the connective tissue, next the migratory amoeboid cells, which are found in the connective tissue of the lungs as well as elsewhere, and which carry the black pigment with them wherever they go. The residual portion which escapes, being arrested by cells on its way through the lymphatic system, is carried to the root of the lung and enters the lymphatic glands of the mediastinum; here the granules meet an obstacle to their further progress, for the countless lymph-corpuscles with which the glands are stored are ready to take up as many of the charcoal particles as can by any possibility be accommodated in their protoplasm. We may conclude that the influence of inhalations of coal-dust varies in different cases, but may be considered as prominent among the exciting causes of pneumonokoniosis.
The charcoal-grinders and carriers, chimney-sweeps, moulders, iron and glass polishers, and the workers in mother-of-pearl, all suffer more or less from destruction of lung-function. Deposits of oxide of iron have been found in the lungs of operators who have for years used this substance as a polishing pigment. Merkel reports the case of a man who was employed to clean the surface of oxidized iron by scrubbing it with sand: his expectoration was grayish-black, and was found to contain small grains of magnetic oxide of iron; the lungs were found to be indurated with cavities at the apices.
Many other instances of dusty avocations may be mentioned as exciting causes. The polishing of brass is sometimes effected by rollers made of canton flannel which revolve with great velocity, filling the air with fibres of cotton which are capable of acting as mechanical irritants.
In the sizing process in some cotton manufactories the material is often adulterated with clays or some sort of salt to lessen the glutinous qualities of the flour or tallow, and although the process is carried on in damp rooms to lessen the brittleness of the size, dust prevails, causing irritation of the nose, eyes, and throat. Some interesting observations have been made on this subject by James Y. Simpson, who has especially investigated the hygiene of woollen manufactories. He suggests that these artisans are comparatively healthy because of the oil absorbed while running the machines. In the manufacture of cotton it has been found that in mills where cotton containing dust and dirt is used, as the East India varieties employed in England during the American War, the respiration was affected, and the expectoration of numbers of operatives contained slaty-colored matters, found, on microscopic examination, to contain cotton fibres.
Bakers who have to deal with highly-dried biscuit flour suffer more than those using ordinary brands of flour. But when all has been said, when we consider how many persons live permanently in an atmosphere specially surcharged with dust without showing a symptom of a morbid state of the respiratory organs, and since the epithelial cells of the lungs can contain particles of coal, it demonstrates that foreign bodies may penetrate the lungs without always inducing serious changes. Mineral matter has been found by Riegel in the form of silica in the lungs of a boy aged four, constituting 2 per cent. of the ash left after incineration. In those of a day-laborer aged forty-seven it amounted to 13 per cent., and in those of a woman cook sixty-nine years old it reached 16 per cent. Accepting these figures as accurate, they show a progressive accumulation in proportion to age among individuals breathing dusty atmosphere. Traube thinks that the changes in the lungs of coal-miners may not be produced by the accumulated particles of coal, but by the chemicals contained in coal, and not found in charcoal. In a discussion of this question in London in 1869, Wilson Fox thought it remarkable that in proportion to the number of persons exposed to the inhalation of irritating substances the cases of phthisis were comparatively few, and suggested that a diathetic condition might underlie the entire pathology.
In summing up the evidence bearing on the predisposing and exciting causes of pneumonokoniosis we cannot overlook the recent discoveries of Koch and his collaborators, but may conclude that although there is increasing evidence tending to show that the bacillus tuberculosis is always present in tuberculous pulmonary processes, yet its exact etiological relation cannot be considered as established. We may still hold that when large amounts of inorganic materials are taken into the lungs, particularly if the ventilation or hygienic conditions under which the dust is inhaled are imperfect, certain diverse pulmonary processes are apt to ensue. That phthisis can be thus produced is undoubted, but the nature of the irritant has less to do with the type of the resulting disease than has an inferior or scrofulous constitution, inherited or acquired, or the indulgence in habits directly damaging to the health; since an unvarying specific cause would be more destructive than has been proven, large numbers of individuals escaping any serious effects when equally exposed.
PATHOLOGY AND MORBID ANATOMY.—Whatever be the dust inhaled, the pathological processes set up by it partake of the same essential character, though differing in intensity and in the division of pulmonary tissue principally involved, while the combined inhalation of organic particles may essentially modify the results produced. Examination of the lungs has revealed deposits of various inorganic materials which have been inhaled, such as oxide of iron, indigo, snuff, silica, coal, carbon, etc. A black discoloration of the pulmonary tissue, with or without induration, enlargement, and blackening of the bronchial glands, may, however, have its origin in morbid changes independent of inhaled matter, such as defective elimination of carbon and carbonic acid, with a sort of precipitation of carbon within the tissues.
The black coloration of the lungs, especially in miners, is also partly due to the deposition of a true hæmatoidin pigment in granular form, caused by the irritating particles inhaled setting up changes in the bronchial or pulmonary tissues, resulting in the escape of the coloring matter of the blood either by rupture of capillaries or from transudation of serum. Similar discoloration is often found in cases of chronic bronchial processes independent of a dusty etiology. The most penetrating form of dust is the silicious, on account of its hard, vitreous character. German authors comment on the difference in the power of penetration of mineral coal-dust as compared with charcoal-dust, because the spiculæ of the former are elongated, sharpened splinters. The coloration of the lung from clay-dust does not diffuse itself so readily as coal-dust, yet it possesses more irritating properties and creates more damage.
The morbid anatomy of pneumonokoniosis includes nearly all the pathological processes incident to the pulmonary tissues. The bronchial lesions are those of chronic bronchitis, with thickening of the bronchial mucous membrane, associated with possible ulceration and bronchial dilatations, forming bronchiectasic cavities. These cavities are caused by combined softening of the bronchial tissues with traction from without by the newly-formed fibrous tissue. The bronchial glands may be enlarged to the size of walnuts, and are often perfectly black and gritty on section. These enlarged glands may occasion, through pressure, many changes in the pulmonary tissues. The effect of this pressure is especially manifest in the lymphatic system. The lymph-circulation is further crippled by the accumulation in the lymph-channels of the inhaled inorganic materials. These interferences with the lymph-circulation may be followed by exudation or lobular and interlobular formation of tissue; secondary to these changes the pressure upon the vesicles may cause local congestions, exudations, and even hæmoptysis. By one or all of these processes the expansile power and elasticity of the lung are slowly depreciated, emphysema develops, intertwined with the lesions of acute, subacute, or chronic bronchitis, fibroid phthisis, and atrophic emphysema. Nodules of cretaceous matter can be recognized through the lungs, which are black in anthracosis or gray in silicosis. These nodules occur from the size of a pin's head to that of a pea, and are especially found in the lungs of glass-cutters, sandstone-workers, and grinders. In these cases they consist in part of iron and in part of stone. In sandstone-workers they are composed of silica; the organ feels nodulated, very fibrous, and in some cases actually gritty. The predominant form of pulmonary change is fibroid; hardened districts of advanced cirrhosis occur measuring two inches and upward in length and width, and in depth and thickness nearly as much. These may be rounded, but are not separable from the adjacent structures, the condensation of the tissues lessening without a defining line. On section they appear tough and leathery, most pronounced along the anterior edges of the lungs, and are apt to be covered in by thickened pleura. If the nodules previously alluded to are encysted, fibrous prolongations extend from these cysts into the substance of the lung, the thickening of the lung being greatest in the septa, on the pleural surfaces, and along the course of the bronchial tubes. Sometimes subacute or chronic pleural processes coexist. The caseous masses found in tubercular fibroid phthisis are infrequent in pneumonokoniosis, but in the latter process the pathological changes may be identical with the ordinary forms of phthisis, especially in those individuals who are predisposed to pulmonary affections and those in whom the pathological processes are rapid.
In anthracosis the lung is large and increased in weight; the surface of the pleura has a bluish-black color, contrasting with the coal-black color of the lungs, which are universally pigmented and contain nodules of pigment. When only small quantities of pigment are present, it presents the appearance of dark lines running between the lobules; on section these are very hard and distinct, being about the size of a millet-seed. They are universally distributed throughout the lung, and in some places appear like small masses of charcoal. Upon squeezing the organ a blackish fluid exudes which stains the hands, but the discharge which is found lying in the bronchial tubes is often yellow and muco-purulent, although the sputa during life is more or less discolored. When the distribution of the discoloration of anthracosis is investigated, it is found to closely correspond with the lymphatic distribution of the lung, and the conclusion is probably well founded that all other irritating particles pursue the same course through the pulmonary tissues. When particles of coal or pigment enter the bronchi with the air, they cannot pass through its mucous membrane, because the basement membrane and fibrous coat underlying it present an obstacle to their lodgment, whilst the cilia of the epithelium tend to prevent their retention in the bronchi; they therefore enter the vesicles, and may be found sticking to the walls. In this way the exemption of the bronchi from pigmentation, even down to the smallest ramifications, can be explained. The interlobular septa ate also the seat of great pigmentation. The germinating epithelium elevates the cells slightly above the surface, and in the interspaces between them the pigment insinuates itself, and thus enters the underlying plasmatic or lymphatic spaces; or the pigment may be incorporated into the epithelial cells, which transfer it to the underlying lymph-space. Once the pigment has found entrance to these lymphatic channels, it is carried by them through the lymphatic vessels in the sheath surrounding the bronchial tubes and the small branches of the pulmonary artery, and in the interlobular septa to the bronchial glands. In this manner the special distribution of the coloring matter in these situations is explained. The special deposit around the small branches of the pulmonary artery is owing to the double set of lymphatics, the peribronchial and the perivascular, which form an anastomosis. The perivascular set is the larger; consequently the pigment passes into them more readily, forming the nodules. Pigment is also found in small quantities around the bronchi, which can be accounted for by the anastomosis of the lymphatics. The bluish-black appearance of the pleura and the distribution of the pigment only in the deeper layers of the visceral pleura are susceptible of a similar explanation, because the deeper layers of the pleura contain lymphatic vessels which are directly continuous by means of the lobular septa with the large perivascular branches of the lymphatic system.
The consequences of the obstruction to the lymphatic and pulmonary-artery circulation may be very serious. In grave cases the lung breaks down, forming a gangrenous-like cavity, which differs from an ordinary cavity in not being rounded; it is more like a gangrene or slough. In a few cases the pathological appearances indicate phthisis, chiefly interstitial, with formation of cavities; sometimes traces of cavities are found which have cicatrized. More commonly oedema is developed in the lung and the bronchial passages. As a consequence of combined bronchial irritation from continuous inhalation of inorganic particles, and the consequent oedema, a continuous germination and shedding of the bronchial epithelium—a chronic bronchitis—associated with emphysema, is maintained. The mechanical cause of this bronchitis—more or less impediment to the vascular and lymphatic circulations by the pigment deposit—is capable of explaining the persistence of various forms of bronchial processes in anthracosis and in other forms of pneumonokoniosis after the patient has ceased working in a dusty atmosphere.
SYMPTOMATOLOGY.—Pneumonokoniosis does not present a special symptomatology. The course of the various morbid processes is insidious and slowly progressive: the development of any of the forms of pulmonary disease depends largely upon the degree of exposure to the exciting causes, or the inherited tendencies, or the susceptibility to influences liable to diminish general vitality or affect the personal hygiene.
The earliest objective symptom of pulmonary lesion is cough, especially recurrent in winter, accompanied by expectoration, which is whitish, frothy, or stringy in character. Gradually the physical signs, taken together with the symptoms, indicate the various forms of bronchitis, acute, subacute, or chronic, sometimes associated with emphysema, bronchorrhoea, or bronchial dilatation. In other cases the symptomatology is that of asthma, either purely spasmodic or secondary to emphysema or cardiac degeneration. In true anthracosis dyspnoea is a marked symptom, and perhaps the accumulation of pigment may interfere with the oxygenation of the blood, or dyspnoea may be due only to an emphysematous pulmonary tissue. The sputa will be black so long as the subject is working in an atmosphere loaded with pigment.
Fibroid phthisis is frequently associated with atrophic emphysema, and the clinical history corresponds with that which is commonly observed in these diseases. Hæmoptysis is rare, but if it occurs it suggests the addition of some tubercular element; a purulent nummular sputa is a suspicious sign of similar import. The symptoms and physical signs of dry pleurisy are to be expected whenever any form of the phthisical process supervenes. The cavities in the lungs are usually bronchiectasic, unless tubercular phthisis occurs as a complication, and the physical signs need no comment. Subacute and chronic laryngitis with ulceration complicate certain cases, particularly those which have inherited or acquired a tubercular tendency.
DIAGNOSIS.—The diagnosis involves a comparative examination of the etiology and the physical signs.
PROGNOSIS.—The prognosis depends very largely upon the withdrawal of the sufferer from an unhealthy environment. In each single case the inherited tendencies, the personal constitution and habits, must be the basis for an opinion upon the gravity of the pulmonary processes and the possibilities of restoration to health. The progress of the disease may be materially retarded or arrested by withdrawal from the occupation involving the inspiration of dust, and restoration to comparative health after years of invalidism is possible for these victims of dusty avocations, even after serious damage has taken place in the lung, if suitable hygienic conditions can be obtained.
TREATMENT.—The treatment of pneumonokoniosis divides itself into the prophylactive and the curative. In works devoted to the hygiene of occupation careful directions are given in reference to methods designed to prevent the dust from entering the respiratory passages. This is partly accomplished by the use of masks or respirators, which possess the obvious disadvantages of clumsiness and interference with respiration. Various devices may be employed in different avocations to prevent the generation of dust, but the most practical plans consist in thoroughly ventilating the atmosphere, and thus preventing the dust from reaching the artisan. Aside from these, the management of the various pathological conditions must be based upon the general principles which govern the treatment of pulmonary processes.