Document RprYgLJqK63kQ8ObkNBxyRQx8

FILE NAME Kent KNT DATE 1956 DOC KNT148 DOCUMENT DESCRIPTION Book Excerpt - Occupational Diseases Asbestosis - Preventive Medicine and Public Health TREVENT MEDIUINT AND Oo PUBLIC HEALTH 07 07 ( Dos 07 ar i KENNETH F. MAXCY M.D. DR P.H. Professor Emeritus of Epidemiology The Johns Hopkins University School of Hygiene and Public Health With 27 contributing authors EIGHTH EDITION APPLETON NEW YORK INC 1956 1050 OCCUPATIONAL DISEASES dust occurs Laboratory experiments on animals carried out in the author's laboratory have shown that exposure of rats to high concentrations of silica dust does not lower their resistance to pneumococci Type I injected intrabronchially In fact under some conditions the rats were more resistant to the lobar pneumonia following prolonged exposure to silica dust The relation of silicosis to bronchopneumonia is not clear TREATMENT and Prevention There is no known treatment for silicosis which will reduce the fibrosis although relief of symptoms to some degree may be obtained in some cases Because aluminum dust produces a coating on silica particles the inhalation of aluminum dust has been tried as a therapeutic measure The Council on Industrial Health and the Council on Pharmacy and Chemistry of the American Medical Association summarized the available data in 1949. Their con- clusions were as follows Studies on the therapy of silicosis thus far have been inadequately controlled The majority of subjects have reported subjective improvement apparently of psychic origin No convincing evidence of objective improvement either of pulmonary function or by roentgen ray has been forthcoming Certain cases have shown eventual progression by roentgen ray subsequent to aluminum therapy under present conditions of dosage Brown and Van Winkle 1949. Prevention is the only positive means of attack on silicosis With modern engineering technics there is no reason why silica exposures cannot be reduced to safe concentrations and silicosis completely eliminated in the course of a few years Until that time comes all persons working in such atmospheres should be examined clinically and radiologically at frequent intervals by a competent physician Those with silicosis should be protected from further exposure to silica dust Persons with tuberculous lesions should not be employed where silica exposures exist Measures for the prevention of exposure to dusts and fumes including silica dust are discussed under prevention of occupational diseases due to chemical substances on pages 1086 to 1091 ASBESTOSIS Asbestosis is a pneumoconiosis due to the inhalation of asbestos dust Nature of Asbestos Asbestos is a general term which is applied to minerals of fibrous form These minerals are silicates of varying composition which fall into two distinct groups serpentine and amphibole Chrysotile a hydrous magnesium silicate of the serpentine type is by far the most common type of asbestos The amphibole group includes various silicates of iron calcium magnesium and in some cases sodium examples are crocidolite and tremolite Asbestos fibers are usually from 20 to 500 microns in length and from 0.5 to 50 microns in diameter The fibers of crocidolite are much stiffer and straighter than those of chrysotile Reaction of Tissues to Asbestos Pulmonary fibrosis results in man and in some animals from the inhalation of chrysotile the serpentine type of asbestos This fibrosis differs from that which occurs in silicosis being a fine interstitial diffuse fibrosis around the terminal bronchioles rather than nodulation It is believed that fibers up to 200 microns in length can penetrate the respiratory tract if the maximum diameter does not exceed 5 microns Fibers which are inhaled accu- mulate in the lumen of the respiratory bronchioles and later in the alveolar ducts but do not seem to penetrate to the alveoli It is ge long fibers lung tissue of the fibe the fact th other tissu they do no particle siz bronchioles Fibrosis oc fibers Con longed exp Clinica comitant p dyspnea w of weight a involvemen tion of exp Diagno the clinical bestosis b fibers whit tured to gi including a ated with t Althou there is no increases sa associated Great Brit asbestos in There i dust is the Incider environme posure Th The incide More than in asbestos the maxim vary with t Sidero " siderosis mentation ever roent shadows si THE DUSTS 1051 flexibility It is generally believed that the fibrosis is due to the mechanical irritation of the long fibers between 20 and 50 microns in length Presumably the motion of the lung tissue in breathing combined with the filamented structure and the of the fibers are responsible for this irritating effect This theory is supported by the fact that asbestos fibers unlike silica dust are inactive when in contact with other tissues such as the liver where there is no mobility and by the fact that they do not cause pulmonary fibrosis if the fibers are short or are ground to small particle size The stiff straight fibers of crocidolite do not stay in the walls of the a bronchioles but pass on into the alveoli and do not appear to cause fibrosis Fibrosis occurs only where there is mechanical rubbing of the tissue against the fibers Commercial talc or its component materials such as tremolite after pro- longed exposure appears to cause fibrosis resembling asbestosis Clinical Aspects The clinical symptoms are due to the fibrosis and the con- comitant pathological changes chiefly emphysema and bronchiectasis dyspnea which can lead to disablement is the chief Progressive of weight also occur Death is due symptom Cough and loss to secondary respiratory infection or to cardiac involvement It is generally believed that the fibrosis will not progress after cessa- tion of exposure 4 Diagnosis of asbestosis must rest on a history of exposure to asbestos dust on st : the clinical symptoms and on the radiological examination The presence of as- bestosis bodies in the sputum is not of any diagnostic value Asbestosis bodies fibers which are surrounded by an containing coating and which have are frac- tured to give peculiar structures They may be formed from any fibrous material including asbestos but are neither indicative of the degree of exposure nor associ- ated with the fibrosis Although some cases of tuberculosis have been reported in asbestos there is no workers convincing evidence either clinical or experimental that asbestosis increases susceptibility to tuberculous infection associated with asbestosis have been found in A number of cases of lung cancer Great Britain various autopsy studies especially in Authorities differ in their opinion regarding the possible role of asbestos in the etiology of lung cancer There is no known treatment for asbestosis prevention of dust is the only effective exposure to asbestos weapon against this condition Incidence of Asbestosis The incidence of asbestosis in persons working in environments containing asbestos dust varies with the extent and duration of ex- posure The disease does not usually appear until after 5 to 10 of The incidence of asbestosis increases years exposure More than half of the progressively with the duration of exposure workers with 20 years of exposure have the disease Studies tihne amsbaexsitomsumindsuasfteries indicated that 5,000,000 particles per cubic foot of air is concentration but recent work suggests that the standards vary with the percentage of long particles in the dust may , OTHER HARD ROCK AND MINERAL DUSTS Siderosis Exposure to iron oxide produces a benign pneumoconiosis called siderosis By itself this mineral provokes no significant fibrosis but mentation which has no influence merely pig- on pulmonary function Gardner 1940 How- ever roentgenograms of workers exposed to the iron oxide dust show shadows simulating those of silicosis Clinical studies of nodular these workers autopsy