Document km9gYQVL3r6MMmjMazjzNXmpB

206 MARGARET R. BF.CKLAKE always call attention to tlte possible association with asbestos exposure. A systematic classification of the radiologic changes associated with asbestos exposure em bodying most of the features described, together with the pleural changes, was developed for epi demiologic purposes, first as the UlCC/Cincinnati classification (167), later adopted as the 1LO U/C classification (168). Its features in clude a reading sheet, an extended 12-point scale to grade parenchymal changes, and stan dard films to assist in the evaluation of pleural and parenchymal changes (obtainable from the International Labour Office, Occupational Safe ty and. Health Branch, CH 1211 Geneva 22, Switzerland. Price: Sw Francs 250.-) The use of this classification, by improving precision and probably also comparability between studies, has enhanced the value of the X-ray as an epi demiologic tool (169). Thus, it enables a better placement of the film in the multidimensional "continuum which extends from complete `nor mality' at one end to the most severe degree of abnormality at the higher" (Bohlig 7, p. 25). In particular, it has permitted the exploration of the exposure-dose relationships (using the chest radiograph to measure response) in working populations. In addition, this classification has been adopted by compensation boards in several countries to improve consistency in the reading of the chest radiograph and should be used whenever the evaluation of a person's films must be considered relative to those of others. It must be emphasized, however, that this classifi cation is descriptive and not diagnostic; further more, although radiologic changes so described relate reasonably well to lung function changes in population studies (87, 95), their relation ship to disability, which is likely to vary con siderably from subject to subject, has not been widely studied. Lung Function Lung function tests have been applied to the study of asbestosis since their general introduc tion to clinical medicine in the 1940s. In gen eral, there are 4 clinical areas of application (10): first, for diagnosis and assessment of dis ability; second, for following the evolution of disease with time; third, for the surveillance of healthy workers, with a view to detecting early changes; and fourth, for preemployment exam ination to screen the "susceptible" person. In addition, information gained from epidemi ologic studies using pulmonary function test ing to determine exposure-response relation ships has permitted inferences trj be drawn about early effects ol asbestos on the lung, in formation lh.it ntav ultimately have considerable practical value in terms of the worker's health. Uingnoiis. Interstitial fibrosis associated with exposure to asbestos is generally believed to be associated with the restrictive and "alveolar capillary" block patterns of pulmonary func tion, similar to that seen with the interstitial fibrosis from other causes (Becklake, 7, p. 3). Characteristic features of the established case (with clinical and/or radiographic evidence of disease) are: general restriction of lung vol umes, particularly vital capacity (VC), with less effect on residual volume; decrease in flows, such as 1-sec forced expiratory volume (FEVj), in proportion to the decrease in VC, so that the ratio of FEV, to forced vital capacity (FVC) is relatively well preserved; decrease in diffusing capacity, attributable in part to the decreased lung volume (170), although decreased mem brane transfer and inhomogeneity of regional ventilation-perfusion relationships within the lung undoubtedly contribute to the impaired gas transfer (43, p. 379). Impairment of gas exchange capability, reflected by arterial desatura tion, increased alveolar-arterial Pot gradient, and hyperventilation, may at first be evident only under the stress of exercise, but later occurs at rest. The CO;, exchange is not usually affected, and arterial C02 retention is not usually a fea ture of the established case. Although there is no evidence to suggest that asbestosis due to chrvsotile is any different from that due to other fibers, one epidemiologic study suggests that there may be greater decrease in function for equivalent estimated exposure to crocidolite compared to chrysotile (94), a dif ference that could be explained by greater re tention of crocidolite compared to chrysotile for equivalent estimated exposure; however, in the light of the potential and, indeed, inevitable inaccuracies that beset all efforts to evaluate remote past dust exposure, in amount and/or nature of the fiber, this interesting observation requires further confirmation before it is assumed that different fibers have different fibrogenic potential in man. It is usually claimed that airway obstruction is not a feature of asbestosis (10, 170-172); however, a review of 375 published cases (173), most with unequivocal parenchymal radiologic changes, indicated that a considerable number of patients had airway obstruction (11 per cent '. f F j ' ( y .-. com terr, pait tion epic (>--. tlisa Jogi. ber tion no i obst com and post tion The doei tion T of h date tion by t In c logit tribi er's crea: forn out relu tos dbebestimp, nurr is ' this A beta may lunj mea ties) prei imp tion him eral nor. preblot Likbre;