Document RaMZ7ZX4g0rNdLmJKLxayxzyX

Thorax. 1983. 35, 644-652 Epidemiological study of respiratory disease in workers exposed to polyvinylchloride dust C A SOUTAR, L H COPLAND. P E THORNLEY. J F HURLEY, J OTTERY. W C. F ADAMS, AND B BENNETT From the Institute of Occupational Medicine, Edinburgh, and Imperial Chemical Industries Limited abstract The respiratory health of workers exposed to polyvinylchloride (PVC) dust has been investigated in 818 men sampled from the work force of a factory manufacturing PVC. In a crosssectional survey, the lung function and prevalences of respiratory symptoms and chest radiographic abnormalities were compared with estimates of individual PVC dust exposures based on detailed occupational histories and current measurements of respirable PVC dust. Complaints of slight exertional dyspnoea were associated with PVC dust exposure, though age and smoking effects were much stronger. Theiforced expired volume in one second (FEV,) and forced vital capacity VC) were inversely related to dust exposure alter age. Jieieht. and smoKintreffiects had been taken mto account. This effect was seen principally in cigarette smokers, and there was suggestive evidence that PVCdusTt exposur-e-and-cigaretie smoking interacted in the reduction of FEV, and FVC. Gas transfer factor was not related to dust exposure. The chest radiographs were read according to the ILO U C classification by three experienced readers. One reader recorded a low prevalence of small rounded opacities, and these were not related to age or dust exposure. Another reader recorded a higher prevalence of small rounded opacities category Oil or more, and these were related to age but not to dust exposure. The third reader recorded the highest prevalence of small rounded opacities (though none greater than category 1.1), and these were independently related both to age and to PVC dust exposure, indicating an effeqt_of PVC dust on the appearances of the chest radiograph. These appearances were so slight that only the higher sensitivity of this leader in the interpretation of profusion of small rounded opacities on the ILO U,C scale enabled detection of this effect of PVC dust. In conclusion, exposure to PVC dust is associated with some deterioration of lung function, slight abnormalities of the chest radiograph, and complaints of slight dyspnoea. The mean decline in l-EV, associated with the average dust exposure experienced in the study was small, though some of the men with higher dust exposures may have suffered clinically important lass of lung function as a result of their occupation. The dust produced during the the manufacture of polyvinylchloride (PVC) includes a large pro portion by number of small particles of respirable size 1 2 Administration of PVC dust to animals has been reported to cause inflammatory changes of the bronchioles and alveoli, including a proli feration of histiocytes and granulomatous lesions.' ' and PVC formulations have been found to have cytotoxic effects in vitro 11 ' These effects were caused in part b> the plasticisers, stabilisers, and other additives in the PVC. and there is some evidence lhal the in vitro toxicity of PVC A J fur repr.nr rcM.ieMv f)r C'A Souur, Itumuic W < k .i rut tonal Mdi'i.tne. Rn*huri:n Pl..c, 1 vlmburyh ! HR vsl. dust is related to the presence of surfactant in the formulation.* Cast reports10 n have described pathological changes in the lungs of workers exposed to PVC dust. In several surveys of PVC workers increase of respiratory symptoms, abnormalities of lung function and of the chest radiograph have been described, although these findings have been dif ficult to evaluate, principally because of lack of satisfactory control groups, failure to take udeiiuate account of the effects of age. cigarette smoking, or general atmospheric pollution, and lack of clarity in descriptions uf radiographic readings - I: Epidemiological sm Methods yn/or popvlatioThe sampff m*ie 1979 from 1501 pensioners (men manufacturer, m. of age) who had i 468 men leaving I Men were selccategories of cui from factory ret of dustiness base, measurements o dusts. The sam; all men with he proportions of t! hundred and fifu dust exposures were replaced h\ exposed groups Finally 818 m currently empl< men who had It menf ( leavers' carbon monoxi sampled propur exposure categ< EVVIRCNMEV I si Current person dust were mea^ in which PVC Preliminary est subjective obse on particle sizt sion and emu: sampling effort ently more d packing, and i One hundr. samples of refrom men in 4 penods on Su filters (type ! 8-0 pm, msc cyclone.Ih fraction of air Johannesburg all particles meter of I uc, greater thar MEOICAL M kv A full occur Medical Res piratory S-' I r t Lpidemiotogi. ol Study of respiratory disease in workers exposed to polyvinylchloride dust 645 Methods trained clerk. J STUDY POPULATION The sample to he studied was selected in January 1979 from 15d 1 currently employed men, 339 pensioners (men who received a. pension from the manufacturer, most of whom were over 60 years of age) who had retired since 1 January 1967, and 468 men leaving for other reasons since that date. Men were selected for study according to broad categories of cumulative dust exposure derived from factory records and preliminary estimates of dustiness based on inspection of the plant and measurements of size ranges of typical PVC dusts. The sampling scheme aimed to include all men with heavier dust exposures, and lesser proportions of those with lighter exposures. One hundred and fifty-six men with high or moderate dust exposures did not attend for survey, and were replaced by reserves drawn from moderately exposed groups. Finally 818 men were studied, comprising 663 currently employed men, 98 pensioners, and 57 f men who had left for reasons other than retire- (ment ("leavers"). Single breath gas transfer for carbon monoxide was measured in 332 men * sampled proportionally but randomly from each exposure category. 4 i ENVIRONMENTAL SURVEY Current personal exposures to respirable PVC dust were measured by occupation in each plant Forced expiratory volume in one second (FEVj) and forced vital capacity (FVC) were measured using a modified Gaensler spirometer." The best of three measurements was used for the analysis. Single breath transfer factor for carbon mon oxide (Tlco) was measured by the breathhold ing method2" based on the modified Krogh technique (Transfer test B. PK Morgan Ltd., Chatham, Kent). Effective alveolar volume (Va) was measured by helium dilution in the same single breath, and used in the calculation of Tlco and Kco. The means of two observations were used in the analysis of these measurements. A full-size postcro-anterior chest radiograph was taken by a standard technique (95--120 kV). The chest radiographs were read independently using the ILO U/C International Classification of Radiographs of Pneumoconioses21 by three readers highly experienced in this work. The readers had all been shown previously to pro duce readings that correlated with measurements of dust exposure in coalminers and to be highly consistent in their readings when presented with the same films on separate occasions. They did, however, represent a range of interpretation of profusion of small opacities recorded using the IL.O U/C scale, and were known to differ con sistently from each other in the prevalences of small rounded opacities they recorded. in which PVC was manufactured or processed. f Preliminary estimates of dustiness were based on- pvt DUST INDEX subjective observation by the sampling team anif" Every occupation within the population under I on particle size measurements of typical suspen study was allotted a PVC dust concentration on sion and emulsion PVC dusts, and the major the basis of the measured current dust levels. sampling effort was directed towards the appar Sixty-six such job/dust categories were derived ently more dusty occupations in the drying, from the measurements made and from knowl packing, and mixing areas. edge of the factory conditions. One hundred and thirty reliable personal A "dust index" was derived from the current samples of respirable PVC dust were obtained dust measurements and the occupational history from men in 44 different occupations for full shift such that the current dust levels in each of a periods on Sartorius cellulose ester membrane man's occupations in the plastics factory was filters (type 11301). diameter 37 mm, pore size i 80 pm. inserted into a Casella Simpeds 70 i cyclone.1" This device samples a "respirable" multiplied by the years he had spent in that occupation, and this figure added to the figures derived from his other occupations in the factory. i fraction of airborne dust in accordance with the Johannesburg Convention.17 including 103^ of STATISTICAL METHODS ! all particles with an equivalent aerodynamic dia meter of I Mm. 50".. of those of 5 Mm. and none greater than 7 Mm. The data were studied initially by cross-tabula tions, graphical methods, and summary descrip tive statistics. Multiple linear regression analyses < * of the lung function results were carried out. medical survey with subsequent examination of residuals. The A full occupational history was recorded, and the radiographic and respiratory symptoms results I Medical Research Council Questionnaire of Res were studied b> maximum likelihood logistic piratory Symptoms" was administered In a .tnalvsis 22 646 C A Soutar etd\ Efidrmiologit Results ENVIRONMENTAL SURVEY Respirable dust levels were highest in the older plants and those making polymer by the emulsion method. The highest mean average respirable dust exposure for any occupation over a shift was 2-88 mg/m3 (SD+1-84). The distribution of calculated dust indices (years X mg/m3) for the 818 men studied in the medical survey is shown in fig 1. MEDICAL SURVEY Features of the population of 818 men are set out in tables I and 2. It was noted in preliminary analysis that the number of years worked at the PVC works or work in an outside industry in which noxious materials were used were of trivial importance in explaining the prevalence of symptoms, lung function and radiographic abnormality, after index of dust exposure, age. and smoking habit had been taken into account. Respiratory symptoms Analysis of respiratory symptoms was based cn the answers to the questionnaire. Two hundred and fifteen men (26%) admitted to dyspnoea on exertion grade. 1 ("shortness of breath when hurrying on level ground or walking up a slight hill"). Prevalence was approximately three times higher in the smoking groups (32% in cigarette smokers) than in the non-smokers Table 1 Features of 818 men studied, according la .4 currently employed, pensioner, or other leaver statm. * Dust index is expressed in years x mg/ms, but does not represent actual dust exposure, since only currem, dust levels are known ,> Table 2 Nw Vmts^JjlW Current workers Pensioners Number 663 Mean age l>rs> 44 2 (SD) (10 8) Mean height (cm) 173 0 (SD) (6 3) Mean weight (Kg) 77 7 (SD) (10 3 Mean dust index 13 39 (SD) (12 84) Years at the plant 14 34 (SD) (8 48) Mein FEV, (I) 3 54 (SD) (0 83) Mean FVC (1) 4.62 (SD) (0 88) Mean FEV,/FVC 0 76 (SD) (0 08) 98 63 4 (7 1) 170 2 (5 4) 75 6 (10 8) 14 23 (II 86) 16 63 (8 06) 2 43 (0 73) 3 41 (0 78) 0 70 (Oil) Leavers 57 43 2 (10 2) 171 2 (6 2) 77-4 (13 3) 4 86 (6 69) 5 46 (5 48) 3 53 (0 72) 4 54 (0 80) 0 78 (0 06) 1 *' .| 1 " (10%). A strong age effect was also apparent, prevalence approximately doubling for every 13, years of age in this population. A dust effect was indicated (p = 0054) after adjustment for age:' and smoking, and-this effect was clear in current' cigarette smokers (p<0-02, 10 dust index units increased the estimated prevalence by a factor of about 20%) after allowing for age and life* time cigarette consumption. The dust effect was not demonstrated in the other smoking cate gories. though these differences between smoking categories could have arisen by chance (p<0-5)% 'aMmok.cn Coma i-nokc' Wo vnok.cn Exaiokcn . No relat1 test index sgnitum, a>t' Forced exp Preliminary toss or FF\ categories. t according d * ment statu account in _ account of "oonsumpti> Within t 'was signii (p<0-025) nor "the si index wa models of . More d efTect of d category pensionerferences : have aris. men in s< ' pattern m an inter employm ing (tabicin currer. After ; Fig 1 Frequency of dust indices. Q = number of men with dust exposure =0. Table 3 for emph not show- Variant Height (cp Weight tW Aft t>r> Number of men Lifetime * (1000 Dust indf i t al tjUemiotogical study of respiratory disease in workers exposed to polyvinylchloride dust 647 llo Table 2 Sumfyrs of men and (mean dust indices) of 818 men grouped by age and smoking category, tus* tmts of dust indices are years * mg/m> s ent Ailt groups (.IT) < J5 Wtmokm Gpftm smoker* 41 50 (4 O m (5 :i 3 0 01 V <6 6> 133 15 2) r< -44 41 (6 7) o) IJ (14 7) 4X M2 9) 197(11 3) 45-49 16(8 2) hf) (164) 12(13 8) 33 114 Si ID 114 5) 50-54 ism: 3 hO (16 61 4 (19 4) 41 116 3) 126 (16 2) 55-39 5(13 4) 5? (18 4) 12 m i) 31 (16 31 HUM' 7| 60 r 20 (15 2) 41 (16 9) It Ml 7) 42(18 M (14(16?) AU 148 (8 0) 378 (13 7> 58 (IS 01 234 (14 2) aiH < i: 7>> No relationships were demonstrated between dust index and history of chronic cough or sputum, asthma or history or acute chest iWness. height, weight, and smoking habits (the model in table 3), the overall loss of FEV, associated with one dust index unit (years X mg/m5) was estimated as 0 0041 litres. This would be equiva forced expired volume in one second lent to a loss of 53 ml of FEV, for the mean dust Preliminary analysis indicated different rates of index, additional to the estimated losses caused lass of FEV, because of age between the smoking by age and smoking (26 ml per year in non- categories, and different mean levels of FEV, smokers. 39 ml per year for cigarette smokers sccording to current, pensioner, or leaver employ plus an additional 5-6 ml per year for each ment status. These differences were taken into packet of cigarettes smoked per day throughout nt, account in the regression model, which also took the year). 13 account of height, weight, and lifetime cigarette In currently employed cigarette smokers con vaj consumption. sidered separately (the model in table 4), the loss 'ge Within this framework index of dust exposure associated with dust index was estimated as 84 ent significantly inversely related to FEV, mis of FEV, for similar exposure, additional to iits (p<0-025) (table 3). Neither the estimated size the loss caused by smoking and age. The mean for nor the significance of the regression with dust FEV, loss in this group of men iri relation to fe- index was seriously altered when alternative high dust exposure (40 dust index units or more, vas models of age and smoking were examined. experienced by only 4-3 ?<, of all the men) was te- More detailed analssis examined whether the-* estimated at 260 ml. mg effect of dust index varied according to smoking 5). category and job status groups (current workers, Forced vital capacity pensioners, or leavers). Though the observed dif A similar sequence of analysis to that for FEV, ferences in dust effect in these groups could was followed, with qualitatively similar results. have arisen by chance (p--0-45) the numbers of There was a negative effect of dust index on men in some of the subgroups are small, and the FVC (p<0-l). pattern of positive and negative effects suggested Further analysis of dust effect in the smoking an interaction between dust effect, current and job category subgroups again showed a signi employment at the factory, and cigarette smok ficant adverse dust effect in cigarette smokers ing (table 4). The dust effect was seen principally in currently employed cigarette smokers. After taking into account the effects of age. Table 4 Regression coefficients for dust index against FEVr Expansion of model of regression for FEV illustrated in table 3. Table 3 Regression ot FEVr Different intercepts lor employment and smoking categories allowed hut not shown Coefficients and sigmfis ance of concomitant variables < hanged hale from the mode! described in table 3. b'S -- not significant ot the 10",. level ^'triable Height (cm) height (kg) kfeiyf) f non-snmker* 1 e**smokcr> } other smokers 1 cigarette smoker* Lifetime cigarette consumption (1000 picks) Dull inUet (year* * mg'm i Negressitm Corflit ifnr (1 0434 -0 0032 0 ()2Ni () (MV) 0 OJKV --O 0392 P o ooni - 1) 2 <f (NXJl 0 IHN)f v o oooi v 0 (HHI1 - 0 01 34 0 0041 - 0 OOO) 0 t>:< Clearest r smokers C urreni * orkyrs inu miser) t C.IVCTM niujilfxT) Pensioners numhcrl --0 0065 (3121 (p 0 02) 0 i)2?# (2?) (p- U OX) -0 001 X 14l ) NS Other \tnok er% -4) 0023 (47) VS i- 046# ( 1) ns 0 0154 (8) NS F.\'Stt>ukrrs Son-sntokers -0 0024 (1X5) NS 0 0246 (1 )> NS 0 O'HU ( 361 NS --0 0034 NS 0 01JS (In) NS 0 lH7' (13, NS v . "* . s V f*t ' T A .ir njr ifraiir rtv. t -. i 648 C A SoutaretiX fyidemielogical slim Table 5 Prevalence of categories of small opacities found by three readers in SIS chest radiographs. Radiographs in which both rounded and irregular opacities were found are also represented here in the rounded and irregular categories U: Small rounded opacities Reader Category OH or more 3 i8c 20%) 15 4 (0 49%) 17 5016-11%) HOCategory or more : to-24%) 2 <0 24%) io<i Small irregu'ar opacities Category Oil or more 32 (3 91 %) 53 <6 4S%) 2*) (3 55%) Category HO or more 7(0 36%) 46 <5 62%) 8 (0 98%) Roth rounded oed 1 irregular opacities - Category Ofl or mm \ 4 <0 49%) 0(0 00%) 4 (0 43%) currently working at the factory (p<003). The observed differences in dust effect in these groups could easily have arisen by chance, but an inter action between dust effect; current employment, and cigarette smoking was suggested, broadly similar to that for the FEVj. Other measurements of respiratory function The FEV,/FVC ratio, Tlco, Kco. and Va were not significantly related to index of PVC dust exposure, nor was any sizeable effect indicated. Chest radiographs Small rounded opacities The anticipated differ ences between readers in interpretation of small opacities were apparent (table 5). Reader 17 recorded the greatest prevalence of small rounded opacities: 50 radiographs (6-1%) with category 0/1 or more, 10 (1-2%) with category I/O or more, the latter consisting of six radiographs with category 1/0 and four with category 1/1. Among these 50 radiographs, there was a strong associa tion between classification by reader 17 as cate gory 1/0 or more and classification by either reader 3 or 15 as small rounded opacities cate- gory 0/1 or more (chi-square test, p<0-001V confirming that inter-reader differences in inter pretation of small rounded opacities were differ ences of degree, rather than classification rf unrelated appearances. The readings for readers 3 and 17 showed' clear relationships between prevalence of srail: - -f~r--T----r- rounded opacities and age (p<0 002 and p<0-0M`J J i I.i . r.1 respectively). The observed data are set out a rif d fig 2. For reader 3, after age had been taken.] r. 3 Prevalent into account, there was no relationship with dmt^ ,0(1 or morefound exposure (p=0-83). For reader 17 there was a* strong dust effect even after age had been takes index (p<0 02 into account (p<0 001, 10 dust index units increased the estimated prevalence by a factor of about 35%). Observed data are set out in fig 3. . The dust effect varied according to smoking, /was found. Reader 15 c showing small fications were status (p<002). and was not observed among Small irreguh current cigarette smokers although the age effect was marked. The reason for these differences was clear relation- not apparent. Reader 17 recorded 10 radiographs showing small rounded opacities category 1/0 or greater, and in spite of this small number, a significant relationship with both age (p<0 005) and dust KEY-REAOER CODE *- - 03 X----- 15 *"-* IT t<1 i IS Fig 2 Prevalence of small roun led opacities category Oil or more found by three readersr related to age group. .5 "1 2 m 0 t 14 JKr* l ' ft ei | Efidemioldgical study of respiratory disease in workers exposed to polyvinylchloride dust 649 <%d JfJ r t/Mrt >001). interdifferon of 'lowed small : 0-001 out in taken i dust was a taken units factor i fig 3. io king among effect es was Dun indx Dr < mg/ms) F3 Prevalence of small rounded opacities category Oil or more found by three readers, related to dust inde x. index (p<0 02) (after adjusting for the other) was found. > Reader 15 classified only four radiographs as showing small rounded opacities: these classi fications were unrelated to age or dust exposure. Small irregular opacities Analysis showed a clear relationship between prevalence of small irregular opacities category 0/1 or greater and age for all three readers (fig 4) (p<0 001 for each reader). There was no relationship of prevalence of small irregular opacities with dust index for any of the three readers. For reader 15 the relationship of small irregular opacities with age could in small part he explained by a positive history of chronic cough or sputum (p<0 03), and by history of chest illness (p<0-03). Reader 17 also found a relationship of small irregular opacities with chronic cough or sputum (p<0-06). but no relationship with history of chest illness. For both readers, the age effect remained extremely strong even when these symptoms were taken into account. Reader 3 found differences between smoking categories. Prevalence of small irregular opacities was lowest in non-smokers (0-7%) and highest among other smokers (12-1%). These were not accounted for by the different age distributions of the smoking groups. There was no dust effect. Neither of the other two readers identified smok ing differences. Relationship of lung function to the presence of small rounded opacities Reader 17 recorded small rounded opacities category 0/1 or greater in 50 radiographs. The lung function of these men was significantly reduce.d. The FEV, lowing reater, ificant ! dust -* K i all ry QH eaders. I In y, I'. \*c on Fig 4 Prevalence of small irregular opacities category 0/1 or more found by three readers, related to age. 650 was reduced by a mean of 206 ml (p<0-02 after age, height, weight, smoking, cigarette consumption, and dust index had been i-Ven into account (the less complex model dev nbed in table 3). The FVC was reduced by a mean of 253 ml (p<0-01), using the same nv,je|, and FEV,/FVC ratio analysed on the log va1e was not significantly reduced Tlco and Y< were measured in 21 of these men, and were i found to be significantly reduced. Va was re Ijced in these 21 men by a mean of 309 ml (p,"'r05). Relationship of lung function to the pretence of small irregular opacities Radiographs of 90 men were thought b,, one or more readers to show small irregular opacities 0/1 or greater. The lung function of tf ;se men was significantly reduced. Their mean f EV, was reduced by 205 ml (p<00l) after adju.ting for age. height, weight, smoking category, lifetime cigarette consumption, and dust index (T-- model in table 3). The mean FVC was reduce/ by 142 ml. using a similar model (p<010). Tie ratio FEV,/FVC was also significantly reduced (p<0 0l, by a factor of 0-97). Tlco was r easured in 45 of these men, and was reduced by a mean of 1 -52 ml/min mmHg (p<005). Va aid Kco were not significantly reduced. A utoclave workers The efTect of a history of work on-dhe a_:oclaves (where exposure to vinylchloride monor.er may have occurred in the past) was examine: in the respiratory symptoms, lung function, ard chest radiographic abnormality models. A history of having been an autoclave worker had no demonstrable adverse influence on sy--.ptoms, lung function, or chest radiographic ab-ormalities Thus there was no evidence that ipparent PVC dust effects were the result of exposure to vinylchloride monomer during c.toclave working. Clinical readings of chest radiographs The chest radiograph of one man showed advanced diffuse pulmonary fibrosis. Tr.s man had a chest radiograph taken though he was not in the intended study sample. The r* evance of his disease to his work is currently Sting in vestigated. hrt has not yet been est.-'ished. No cases of lung cancer or active tuK-culosis were detected in the survey Discussion This study was planned to compare c lime C A Soutar etd ' Epidrmiotogica > function, chest radiographic appearances, u< alone is of m prevalence of respiratory symptoms in workoi i' exposure was in a factory manufacturing PVC with estimito pvc-wr-ru. of personal exposure to respirable PVC dust volume. The The random sample was selected from men i ^ dust exposur I had previously worked in the factory as well n 1 variations in . the current work force, and was weighted to include a relatively high proportion of that who had the highest lifetime exposure to PVC dust. These preliminary estimates of exposiflt were based on factory records and a preliminaiy "T'Caused dints . tion in some posures. The was seen r apparent inti inspection of the plants and typical dusts pro . chance but v duced. Twenty-five per cent of selected me,*J>' of dust effec- thought on this basis to have high or moderate 1 gories. Respi exposures, did not attend for examination. V~ food wrapper: Reserves for these men were included, albei V and in one ; that these were from medium rather than higb -T be more con dust exposure groups, to ensure that sufficieit ? ette*.*' ft numbers of men with substantial exposures were interaction f studied. It is emphasised that the dust exposure '! posure repo- est mates used in the analysis were not based effect of pr on these preliminary estimates but on a detailed contaminate occupational history obtained from each maa dusty hands together with measurements of current personal direct evide: exposures in the factory. These estimates, though atmm. the best available, may nevertheless have been Assessmet inaccurate to the ex-tent that previous dust ex* posures may have been higher than there in chest rad Classificatio- presently experienced. In view of probable over The three all changes in dust levels conclusions about quan titative relationships between dust and disease should be drawn with caution. It was not possible in this study to take part in this variability radiographs sistently fr< account of the health effects of the components of the PVC powder other than the PVC itself, nor of changes in the formulation occurring ever the years. The "respirable" fraction of air borne dust measured in this survey is suitable for comparisons with both bronchial and alveolar small roun present stui readers w recorded s chest radio related to disease, for dust in this size range deposits substantially either in bronchial or alveolar zones. Furthermore, measured exposure to "res pirable" coal mine dust has been shown to recorded ' number of was correl The third r correlate with mucous hypersecretion and loss of FEV, in miners.-'-' as well as with the radiographic appearances of pneumoconiosis." The study demonstrated a relationship between * of small n these op. independe each of tl estimates of exposure to PVC dust and dyspnoea, lung function, and chest radiological abnormality. A history of moderate exertional dyspnoea was related to dust exposure, though this relationship was apparent only in cigarette smokers. This effect as additional to the effects of smoking and aging which were, however, the predominant explanatory variables for this svmptom It seems imlikelx that the effect of I'VC dint on symptoms fieally val sensitive recording the detec jtraphic < profusion almost a! 1/1), an. was coft Epidemiological study of respiratory disease in workers exposed to polyvinylchloride dust 651 done is of much clinical importance. PVC dust many cases did not even record their exposure was related to reduction of FEV, and presence. On clinical readings of the radiographs FVC but not of transfer factor or alveolar there were no cases of advanced pulmonary volume. The moan decline of FEV, related to fibrosis among them, except for one man, not in dust exposure *was small, though individual the study population, who did have radiographic variations in response might be expected to have evidence of advanced pulmonary fibrosis. Further caused clinically significant loss of lung func investigation of the cause of this is being under tion in some of the men with high dust ex taken. posures. The effect of dust on lung function Thus PVC dust exposure was associated with was seen mostly in cigarette smokers, an both small rounded opacities on the chest radio apparent interaction which could have arisen by graph and a slight average functional defect. The chance but which was supported by the pattern reduction of FEV, but normal alveolar volume of dust effects among the various smoking cate and transfer factor indicated that the effect was gories. Respiratory disease has been reported in predominantly obstructive in type, but the food wrappers cutting PVC film with hot wires,211 parallel reduction of FVC indicated by the lack and in one report these symptoms appeared to of any relationship between dust exposure and be more common in workers who smoked.cigar the ratio between FEV, and FVC suggested a ettes.12 It is conceivable that the apparent slight additional element of restriction. The radio interaction between smoking and PVC dust ex logical and functional abnormalities were them posure reported in the present study was an selves related, for the 50 men with small rounded effect of products of combustion of cigarettes opacities also had reductions of FEV,. FVC, and contaminated with PVC dust from contact with alveolar volume after the effect of dust had been dusty hands or clothing, though there was no allowed for. While this relationship was not direct evidence from this study of such a mech specific for PVC dust effects, for it was seen anism. predominantly among cigarette smokers whose Assessments of the profusion of small opacities small opacities were not obviously related to dust in chest radiographs according to the TLO U/C exposure, it does tend to suggest that small Classification are known to vary between readers. rounded opacities may be the result of disease The three experienced readers invited to take of bronchioles, sufficiently distal to be radio- part in this study were each known to show little logicallv detectable yet sufficiently. proximal to variability on repeated readings of the same cause an obstructive defect. The parallel reduc radiographs, but were also known to differ con tions of FVC and Va suggest an additional sistently from each other in the prevalences of- restrictive defect, which tends to confirm the small rounded opacities they recorded. In the* distal site of the lung damage, the nature of present study the anticipated differences between which might be similar to the cellular reaction readers were again apparent. One reader reported in one case of a PVC worker with recorded small rounded opacities in very few radiographic shadows." chest radiographs, and these were not obviously By contrast, small irregular opacities, related related to age or dust exposure. Another reader to age and in small part to chronic productive recorded small rounded opacities in a larger cough but not to dust exposure, were associated number of men. and presence of these opacities with a more classical obstructive pattern in which was correlated with age but not dust exposure. the FEV, was reduced substantially more than The third reader recorded the greatest prevalence the FVC. There was in addition a reduction of of small rounded opacities, and it was found that gas transfer factor suggesting the presence of these opacities were related to age and, emphysema or ventilation/perfusion mismatching independently, to dust exposure. We consider Since the later stages of panacinar emphysema each of these readers' assessments to be scienti are usually associated with a diminution rather fically valid, and that the third reader's more than an increase in radiographic lung shadows, sensitive interpretation of the recognition and it is probable that the clinical recognition of recording of small rounded opacities enabled small irregular opacities enables the identification the detection of a relationship between radio- of a type of chronic airflow obstruction associated graphic appearances and dust exposure. The with ventilation/perfusion mismatching. The profusions of these small rounded opacities were pathological basis for the opacities might con almost all of low category (none greaier than ceivably he enlarged arteriovenous shunts. I/O. and the slightness of these appearances We conclude that exposure to PVC dust is was confirmed by the other readers, who in associated with abnormalities of lung function. 652 slight abnormalities of the chest radiograph and complaints of slight dyspnoea. While these results are not unduly alarming, they do indicate that PVC dust exposure should be controlled, and that the men with radiographic abnormalities should be followed clinically to determine future progression or regression of the condition. This study was carried out with the full co operation of the management and workforce of Imperial Chemical Industries Limited to whom we are grateful for financial support. 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