evolution of disability in coalworkers'welsh national school of medicine, cardiff lyons, j. p....

Thorax (1976), 31, 527.

Evolution of disability in coalworkers'pneumoconiosis

J. P. LYONS and H. CAMPBELL

Pneumoconiosis Medical Panel, 9 The Friary, Cardiff; Department of Medical Statistics,Welsh National School of Medicine, Cardiff

Lyons, J. P. and Campbell, H. (1976). Thorax, 31, 527-533. Evolution of disabiity incoalworkers' pneumoconiosis. Retrospective analysis of the results of serial ventilatorycapacity tests (FEVY.O), which had extended over an average period of almost 15 years,has been carried out in 215 miners and ex-miners who suffer with coalworkers' pneumo-coniosis. All were unselected previously diagnosed cases who attend the CardiffPneumoconiosis Panel at regular intervals for re-assessment examinations. They consistedof 68 miners and 147 ex-miners and they were divided into three groups according totheir radiological category at their most recent examination, carried out in either 1973or 1974. There were 90 cases of category B progressive massive fibrosis (PMF), 50 cases

of category A PMF and 75 cases of simple pneumoconiosis. Findings for the 38 life-longnon-smokers within the 215 were compared with those for the smokers.

All three groups showed progressive impairment of ventilation over the whole periodof observation. This was most marked in the category B cases but this group had alreadyacquired a substantial proportion of their eventual impairment while still classifiedradiologically as category A or as simple pneumoconiosis. These findings are not com-

patible with the view that coalworkers' pneumoconiosis does not cause significantimpairment of ventilation until the category B radiological stage is attained; they suggestrather that cases destined to progress to serious disablement show evidence of progressiveimpairment of ventilation at very much earlier radiological stages. Non-smokers showeda pattern of impairment similar to that of the smokers but were less disabled; thedifferences, however, were slight and not statistically significant.

There is general agreement among writers on thesubject that coalworkers' pneumoconiosis can be acause of substantial respiratory disability andpremature death in its later stages, when theradiological assessment has reached at leastcategory 'B' progressive massive fibrosis; butwhether this disease can cause significant disable-ment at earlier radiological stages than this is stillopen to question. Evidence from the Pneumo-coniosis Research Unit of the Medical ResearchCouncil, Gilson and Hugh Jones (1955), Carpen-ter et al. (1956), and Cochrane, Moore, andThomas (1961) indicated that simple pneumo-coniosis per se was probably not a cause of signifi-cant disability, and Cochrane (1973) suggestedthat simple pneumoconiosis together with earlycategory 'A' progressive massive fibrosis causedneither premature death nor significant respira-tory disability.

In contrast, Rogan et al. (1961), Ashford et al.(1968), and Morgan et al. (1971) found evidenceof disturbance of lung function which was relatedto the radiological category in simple pneumo-coniosis, and Lyons et al. (1972) found evidenceof progressive impairment of ventilatory capacityat all radiological stages of the disease which wasrelated to emphysema but not to the radiologicalcategory of simple pneumoconiosis. Many of theaforementioned studies were carried out on work-ing miners, thereby excluding the more disabledand elderly ex-miners, and most of them wereconcerned with a single aspect of lung functiontested at one point in time only. In a chronicprogressive disease like coalworkers' pneumocon-iosis, one might expect that serial tests carried outon the same individuals would be of more value.Serial tests of respiratory function were, in fact,included in the study of Lyons et al. (1972) and

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J. P. Lyons and H. Campbell

also in an earlier study by Higgins and Oldham(1962), but in both of these the period of observa-tion was probably too small (amounting to notmore than five years) for the results to be veryconclusive.

Obviously longer periods of observation shouldprove more revealing concerning the evolution ofdisability in the disease, and since serial tests ofventilatory capacity have now been in continuoususe at the Cardiff Pneumoconiosis Panel since1957, it was thouight that a retrospective study oflung function in miners examined routinely at thePanel might throw some light on the evolution ofdisablement in them. Cases who had reached thestage of PMF at the time of the latest examinationwoUld, it was thought, prove particularly interest-ing, since if disablement is present in such cases itis generally attributable to the disease; and a retro-spective assessment of lung function studies inthem should help to throw some light on the be-haviour of the disease in its early stages. Such astudy should indicate whether or not pulmonarydisablement was present at the time of the earlierradiological categories in those cases showingdisablement at the category B stage.

NIATERIAL

The material consists of 215 unselected cases ofcoalworkers' pneumoconiosis, all of whom hadbeen diagnosed previously and accepted for com-pensation by the Cardiff Pneumoconiosis Panel.Such cases normally should have radiographicchanges amounting to at least category 2 of theILO Radiological Classification of Pneumocon-iosis. All diagnosed cases of coalworkers' pneumo-coniosis are regularly re-examined by the Panel;those cases who show radiographic evidence ofPMF are normally re-examined at two-year inter-vals irrespective of whether or not pulmonarydisablement is present, while cases of simplepneumoconiosis are re-examined every threeyears. For the purpose of the present investigationall such cases, with certain exceptions to beenumerated later, who attended during specificperiods of 1973 and 1974 were included, andmost of these had had serial tests of lung functionover comparatively long periods. In a previouspaper (Ryder et al., 1970), we indicated why, inour view, because of the activities of the NCBRadiological Service, most cases of pneumocon-iosis eligible for compensation should be knownto the Panel, and these reasons apply even moreforcibly to men with progressive massive fibrosis.Hence we believe that such a sample should be

reasonably representative of those categories ofpneumoconiosis in the coal-mining community asa whole in South Wales since it seems most un-likely that a substantial number of potentiallydiagnosable cases could be unknown to the Panelat the present time.The majority of the PMF cases were collected

between June and October 1973, and all of thecases of simple pneumoconiosis plus a few ad-ditional PMF cases were collected between Mayand August 1974. The exceptions were as follows:

(a) cases who were considered to be category Bradiologically over the entire period of physiologi-cal observation, that is, category B before thetime of the first pulmonary function test. Suchcases are recognized to suffer with progressivedisablement, and no purpose relevant to the cur-rent investigation would be served by includingthem;

(b) cases who were too ill to attend at the Paneland were thus seen at home for their routineexaminations were also excluded since recentcomparable ventilatory capacity findings werenot available for them;

(c) cases who had attended the Panel for lessthan six years as it was considered that the periodof physiological and radiological observation wastoo short.

It is recognized that this method of collectionproduces a bias in favour of less severely disabledcases and early category B cases, but this wouldtend to negate any suggestion that the Panel cases

might be biased in the opposite direction. Thecoal-mining population in South Wales is a

notably stable one and so it is unlikely that anysignificant movement of population has takenplace over the period of observation, and deathsdue to the disease will presumably have occurredmainly among the more advanced cases whowould not have been eligible for the survey on thataccount.

METHOD

In all the eligible cases seen during 1973 and1974, there were available a current radiographand a pulmonary function test; the earliest Pneu-moconiosis Medical Panel examination to includea lung function test was then identified and theradiograph contemporary with the first lung func-tion test was selected. In most cases the intervalbetween the first and latest FEV,.O ranged from10 to 17 years and the average period of observa-tion was 14 years. In cases who were consideredto be category B at the most recent 1973/74 exam-

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Evolution of disability in coalworkers' pneumoconiosis

ination, all the radiographs taken during theintervening period were examined and an inter-mediate film which corresponded as closely aspossible with the transitional category A to cate-gory B radiological stage was selected togetherwith its concurrent ventilatory finding. Such casesmight reasonably be interpreted radiologically ascategory A/B and were so termed for the purposeof the investigation. In addition, in the 75 casesof simple pneumoconiosis, the FEV1.0 approxi-mately midway in time between the first andfinal was also recorded. The ventilatory capacitytests were carried out in standardized conditionsusing the Poulton spirometer, virtually all of themby the same highly experienced technician.

All the radiographs were re-read jointly at thesame time especiallly for this study by JPL andWC according to the ILO 1968 classification, butfor the purpose of the paper the numerical cate-gory only has been used. It should be made clearthat in many cases the film taken at the same timeas the first FEV and used in this paper post-dated,sometimes by several years, the film taken whenthe disease was first diagnosed. Thus some caseswho had earlier been diagnosed as showing cate-gory 2 changes by the Panel could be adjudgedas showing only category 1 changes by the presentreaders on the later (first FEV) film. In a fewcases where this occurred it was due to a tendencyto 'overread' earlier films at a time when the ILOradiological classification was in its formativestages, but in others actual regression was ad-judged to have taken place. There were 38 life-long non-smokers within the 215 cases. The ven-tilatory findings for these were compared withthose of the 177 smokers.

RESULTS

There were 215 cases in the study, 75 who weregraded as simple pneumoconiosis (in 1973/74), 50as category A, and 90 as category B. One hundredand forty seven of the men (68%) were retiredfrom coal mining and 68 (32%) were still em-ployed in the industry. Those miners who werecontinuing to work in the industry either under-ground or on the surface were in dust free or dust'approved' conditions, since all were recognized ascases of pneumoconiosis. The ex-miners weremainly men who had retired because of age ordisease but included men who had left the in-dustry while still of working age and were em-ployed elsewhere. The average duration offollow-up since the first pulmonary function test

was 14 8 years for all cases, 14 8 for the simplepneumoconiosis, 14 9 for category A, and 14 7 forcategory B.Table I shows the average age and average

duration of exposure to dust underground foreach of the radiological categories. The averageage of the 215 miners was 60 years and the expo-sure to dust underground 36 years. Although thecases with simple pneumoconiosis were two yearsyounger on average and had three years' shorterduration of exposure to dust, these differenceswere not statistically significant.

TABLE IMINERS AND EX-MINERS: RADIOLOGICAL CATEGORYOF PNEUMOCONIOSIS IN 1973/74, MEAN AGE, AND MEANDURATION OF EXPOSURE TO DUST UNDERGROUND

Number MeanCategory Mean Age Exposure

Total Ex-miners (yr) (yr)

A 50B 90Simple 75

38 76%65 72%44 59%

626058

373733

Table II shows the numerical radiological cate-gory in 1973/74 and at the time of the first pul-monary function test for the three groups. Therewere by definition no men who progressed from

TIABLE ILPROGRESSION OF CASES OF COALWORKERS PNEUMO-CONIOSIS: RADIOLOGICAL CATEGORY AT TIME OFFIRST AND MOST RECENT PULMONARY FUNCTION

TESTS

Simple Cases Category A Category BRadiologicalCategory First Recent First Recent First Recent

0/1 7 5 - - 1 -

1/0 4 2 3 - 1 -1/1 28 25 3 - 3 -1/2 8 13 5 - 1 -

2/1 15 15 8 - 3 -

2/2 11 11 4 - 10 -2/3 2 2 3 - 6 -

3/2 - 2 1 - 3 -

0/A _ _ 2 6 3 -

1/A _ _ 8 17 17 -

2/A -_ 9 21 30 -3/A - - 2 - 10 -

NR/A - - 2 6 2 -

0/B _- - - - 151/B _ - - - - 342/B = = - - - 273/B - - I li zNR/B -_ _ _ 13

75 75 50 50 90 90

Note: NR/A = category A of PMF. Simple pneumoconiosis gradingnot read.

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simple pneumoconiosis to PMF in the first group;

27 out of the 50 men (54%) had progressed fromsimple pneumoconiosis to category A in thesecond group, 28 men (31 %) had progressed fromsimple pneumoconiosis to category B, and 62 men(69%) had progressed from category A to cate-gory B in the third group. There were no regres-

sions in PMF categories.In the reading of the category of simple pneu-

moconiosis there were, however, considerablechanges both upwards and downwards. Of the 75cases of simple pneumoconiosis, 51 (68%) re-

mained in the same broad category, 16 (21%) ad-vanced one broad category, and eight (11%)showed regression of one category. Among the 50cases of category A there were seven cases (14%)in whom the background of simple pneumo-

coniosis was not read, five cases (10%) showedprogression of the simple pneumoconiosis, and 14(28%) showed regression, 24 (48%) remainingconstant. Among the 90 cases of category B,there were 13 (14%) in which the background ofsimple pneumoconiosis was not read, there were

only 5 cases (6%) of progression, and 39 cases

(43%) of regression, 33 cases (37%) remainingconstant.

Radiological regression of simple category ofpneumoconiosis is well recognized as occurring incases with PMF where it is usually attributed toprogressing emphysema and fibrosis. It is not so

widely recognized that similar regression can oc-

cur in cases of simple pneumoconiosis, but itseems that it does occur and is probably broughtabout by the same processes. In the present cases

it is acknowledged that differences in film qualityand of radiological technique may have contri-buted to apparent lack of progression andregression, but the films were on the whole quitecomparable, the bulk of them having been takenwithin the Panel, and the present readers are satis-fied that actual radiological regression had taken

place in some cases, notably in terms ofnodulation.

It seems likely that in miners who have leftsignificant dust exposure, pathological sequelaemay continue to develop without further co-

related radiological progression of the classicalsimple nodular variety. We described and reportedsome evidence to this effect (Lyons et al., 1974)in a group of deceased miners, some of whom hadalso shown radiological regression during life.The primary purpose of this study, however, is

to demonstrate the degree and the progression ofpulmonary disability by men suffering from thisdisease. Pulmonary disability has been measuredby the deficit in FEV1.0 adjusted for age andheight according to Cotes' (1968) formula withineach radiological category. These expected valuesequate fairly well with those determined and usedby Carpenter et al. (1956) in their Rhondda Fachstudy of non-miners aged between 50 and 65, in-cluding those with respiratory symptoms who aregood controls for our miners of similar age, manyof whom actually reside in the Rhondda Fach.The average FEV1.0 of that non-mining popula-tion was approximately 0 2 1 lower than that ofour cases but the annual fall in FEV1.0 for thenon-miners was virtually identical with Cotes'spredicted average figure of approximately 0034 1per annum.

Table III shows the average deficit for eachgroup of patients at the recent examination in1973/74, at the intermediate examination, and atthe first pulmonary function test which was onaverage 14 8 years previously. This deficit is alsoillustrated by the Figure.

All groups of pneumoconiotics show a progres-sive pulmonary disability both at the recent ex-amination and at all the previous examinations.The cases of simple pneumoconiosis and of cate-gory A behave in a similar way with a deficitgreater than their expected value for age of ap-

TABLE IIIPROGRESSION IN CASES OF COAL WORKERS' PNEUMOCONIOSIS: DEFICIT OF FEV,., ADJUSTED FOR

CHANGING AGE: MEAN VALUE ± STANDARD ERROR OF MEAN

Initial FEV Intermediate FEV Recent FEVCurrent Number of

Radiographic Men Years YearsStatus Before Deficit (1/sec) Before Deficit (1/sec) Deficit (l/se>)

Simple 75 14-8 0-42 + 0-06 7-2 0 47 ± 007 062 ± 0-08Category A 50 14-9 0*43 ± 006 NK NK 0 55 ± 0-09Category B 90 14-7 0-52 ± 004 7.5 0 65 ± 005 0-87 L 0-06

NK = not known.All deficits are statistically significant P < 0-001.

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Time of previous mecsurement in yeors Current15 10 5 deficit

75 simple pneumoconiosisA. - 50grode 'A' PMFO 0 25 - --o 90 grode 'B' PMF

0

-Y

-,0 75 - _.

10~~~~~~~~~~~~~~~~~~~~1FIGURE. Mean deficit of FEV1.0 for the three patientgroups.

proximately 600 ml at the recent examinationsand of approximately 420 ml at the first examina-tion 14 or 15 years previously. In this intervalof time the men will also, of course, have lost onaverage 500 ml due to advancing age, and hence600 ml deficit at the age of 60 is a greater disabiltythan 420 ml was at the age of 45. In these casesthe increase in pulmonary disability had been slowand would be hardly perceptible over a period offive years.

In the group of men destined to reach categoryB their recent pulmonary deficit (mean: 870 ml)was greater than was that of the other two groups.Fifteen years earlier these men already had adeficit of 520 ml which was more severe than thatof the other two groups. At the intermediatestage, after seven years when their radiologicalcategory was A/B their deficit had increased to650 ml, which was similar to the deficit of theother groups after 14 or 15 years. Thus this in-creasing deficit in pulmonary capacity was pro-gressive during the whole of the period understudy. It was not a step function with rapiddeterioration at the onset of category B.The average annual increase in the rate of fall

of FEV1.0 over that expected is shown in TableIV. Comparison with Table III will indicate thatin the category B and the simple cases (categoryA cases were not determined) the rate of fall isincreasing with the passing of time, presumablydue to progression of disease or advancing yearsor more probably a combination of both. Thesefindings are consistent with a very slowly progres-sive chronic fibrotic respiratory disease, and itseems probable that disablement may not achievesignificant proportions until the sixth decade, orlater in many cases, a point of practical signifi-cance today because of increased life expectancy.

TABLE IVDISABILITY IN COAL WORKERS' PNEUMOCONIOSIS:

ANNUAL INCREASE IN DEFICIT IN FEV1..Category of Annual Increase in

Pneumoconiosis Follow-up Deficit above ExpectedDeficit due to Ageing

Simple 14*8 years 14 mlCategory A 14-9 years 8 mlCategory B 14-7 years 25 ml

The differential findings for ventilatory impair-ment in cigarette smokers and non-smokers areset out in Table V. All the groups had a deficit inFEV1.0 greater than the expected value, and thisdeficit increased over the 14-year period of obser-vation. The deficit was greater in the smokers thanthe non-smokers in all except the small groupof eight category A cases when considered on theirown rather than in combination with the 14 simplecases when the uniformity is restored. None ofthe differences, however, between smokers andnon-smokers is statistically significant (t<2-0;P>005). In comparing the ventilatory findings ofcigarette smokers and life-long non-smokers, itmust be kept in mind that the expected values ofthe latter may be up to a litre more than that ofthe smokers (Wilson et al., 1960). Insofar as thepresent cases are concerned, since the largestdifference between the groups at any point is0-46 1, and usually considerably less, it seemsreasonable to assume that there is impairment ofventilatory capacity in all of the cases which isnot due to the effects of smoking, and which isprobably affecting both smokers and non-smokersin equal measure, the most probable cause of thisbeing pneumoconiosis.

DISCUSSION

It might be argued that at least some of the ven-tilatory impairment in our cases may have beendue to dust-induced disease other than pneumo-coniosis, notably chronic bronchitis, but we are

unaware of any conclusive evidence to this effect.The Special Committee of the Medical ResearchCouncil (1966) set up to investigate this matterwas unable to find that intensity of dust exposurewas a significant factor in determining the pre-valence of chronic bronchitis in coalworkers.Rogan et al. (1973) found an association betweenincreasing dust exposure and ventilatory impair-ment without radiological evidence of pneumo-coniosis. but this does not mean that the earlier

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TABLE VDISABILITY IN COAL WORKERS' PNEUMOCONIOSIS: SMOKERS AND NON-SMOKERS: DEFICIT IN FEVL.o (1/sec)

Initial Deficit Recent DeficitCategory of

Pneumoconiosis Smokers Non-smokers All Smokers Non-smokers All

Simple 0-48 (61) 0-12 (14) 0-42 0-71 0 25 063PMF (A) 039 (42) 0-61 (8) 0-43 0.51 074 0 55Simple + PMF (A) 0 45 (103) 0131 (22) 0-42 0-63 0 43 0.59PMF (B) 0 54 (74) 0-41 (16) 0 52 092 0-66 0-87

Non-smokers = never smoked more than one cigarette per day for one year.Number of cases in brackets.

pathological changes of pneumoconiosis were notalready present.Many authors have described finding established

simple pneumoconiosis at necropsy in so-calledcategory 0 cases. Lyons et al. (1972; 1974), Naeye(1972), Heitzman et al. (1972), and Gough, James,and Wentworth (1949) maintained that widespreadfocal emphysema may have no radiologicalcounterpart. It seems quite conceivable, therefore,that some degree of impairment of ventilatorycapacity due to pneumoconiosis may be present insome cases before significant radiological changesare manifest. Such would be quite consistent withour present findings as the Figure might suggest.The degree of ventilatory impairment present inthe cases at the beginning of the period of observa-tion coupled with the subsequent abnormal annualfall of FEV.0 indicates that the impairment insome must have begun considerably earlier thanthe time of the first FEV and presumably at amuch earlier radiological stage, possibly even apre-radiological stage.

It is difficult to reconcile the ventilatory findingsin these category B cases with the view thatneither the simple nor the category A stages ofcoalworkers' pneumoconiosis cause respiratorydisability while accepting that the category Bstage does. Our evidence suggests that casesdestined to progress to category B show evidenceof it long before that category is reached, and webelieve that retrospective assessment of existingcategory B cases will, in general, show this to bethe case if serial physiological observations arecarried out. Only one case with a normal FEV atthe A/B stage exhibited the average deficit of0 84 or more at the category B stage.The separate groups of category A and simple

pneumoconiosis cases are less disabled than thecategory B cases, despite approximately similardust exposure and age groups. They are presum-ably less susceptible to the effects of dust for con-stitutional and other reasons which may not be

apparent. It seems reasonable to conclude, never-theless, having regard to the reduced average ven-tilatory findings and the increasing fall in FEVper annum, that a proportion of cases must besignificantly disabled on an individual basis, andalso that some cases may not show significantdisablement until comparatively late in life. Onthe other hand, it seems that an increased rateof fall of FEV starts at an early stage of thedisease, and it may be that serial observations ofventilatory capacity might prove more valuablethan radiology in the early detection of susceptiblecases.

We are indebted to Dr. James Carmichael, ChiefMedical Adviser to the Department of Health andSocial Security, for permission to publish and to usethe Panel material; to Mr. W. G. Clarke, MBE, forassistance in reading the radiographs; and to Miss C.Squance, Cardiff Pneumoconiosis Medical Panel, forsecretarial assistance.

REFERENCES

Ashford, J. R., Brown, S., Morgan, D. C., and Rae,S. (1968). The pulmonary ventilatory functionof coal miners in the United Kingdom. AmericanReview of Respiratory Diseases, 97, 810.

Carpenter, R. G., Cochrane, A. L., Gilson, J. C., andHiggins, I. T. T. (1956). The relationship be-tween ventilatory capacity and simple pneumo-coniosis in coalworkers. British Journal of Indus-trial Medicine, 13, 166.

Cotes, J. E. (1968). Lung Function, 2nd edition,p. 377. Blackwell Scientific Publications, Oxford.

Cochrane, A. L. (1973). Relation between radio-graphic categories of coalworkers' pneumo-coniosis and expectation of life. British MedicalJournal, 2, 532.

Cochrane, A. L., Moore, F., and Thomas, J. (1961).The prognostic value of radiological classificationin cases of progressive massive fibrosis. Tubercle,42, 64.

Gilson, J. C. and Hugh Jones (1955). Lung functionin coalworkers' pneumoconiosis. Medical Re-search Council Special Report Series, 290.

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Gough, J., James, W. R. L., and Wentworth, J. E.(1949). A comparison of the radiological andpathological changes in coalworkers' pneumo-coniosis. Journal of the Faculty of Radiologists,1, 28-39.

Heitzman, E. R., Naeye, R. L., and Markarian, B.(1972). Roentgen pathological correlations incoalworkers' pneumoconiosis. Annals of the NewYork Academy of Sciences, 200, 510.

Higgins, I. T. T. and Oldham, P. D. (1962). Ventila-tory capacity in miners. British Journal of In-dustrial Medicine, 19, 65.

Lyons, J. P., Ryder, R. C., Campbell, H., Clarke,W. G., and Gough. J. (1974). Significance ofirregular opacities in the radiology of coal-workers' pneumoconiosis. British Journal ofIndustrial Medicine, 31, 36.

Lvons. J. P., Ryder, R., Campbell, H., and Gough, J.(1972). Pulmonary disability in coalworkers'pneumoconiosis. British Medical Journal, 1, 713.

Morgan, W. K. C., Burgess, D. B., Lapp, N. L., andSeaton, A. (1971). Hyperinflation of the lungsin coal miners. Thorax, 26, 585.

Naeye, R. L. (1972). Types of fibrosis in coalworkers'pneumoconiosis. Annals of the New YorkAcademy of Sciences, 200, 381.

Rogan. J. M., Ashford, J. R., Chapman, P. J.,Duffield, D. P.. Fay, J. W. J., and Rae. S. (1961).Pneumoconiosis and respiratory symptoms inminers at eight collieries. British Medical Journal,1, 1337.

Rogan, J. M., Attfield, M. D., Jacobsen, M.. Rae, S.,Walker, D. D., and Walton, W. H. (1973). Roleof dust in the working environment in develop-ment of chronic bronchitis in British coal miners.British Journal of Industrial Medicine. 30, 217.

Ryder, R., Lyons, J. P., Campbell, H., and Gough, J.(1970). Emphysema in coal workers' pneumo-coniosis. British Medical Journal, 3, 481.

Wilson, R. H., Meador, R. S., Jay, B. E., and Higgins,E. (1960). The pulmonary pathologic physiologyof persons who smoke cigarettes. New EnglandJournal of Medicine. 262, 956.

Requests for reprints to: Dr. J. P. Lyons, Pneumc-coniosis Medical Panel, Prudential Building, 9 TheFriary, Cardiff.

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