Relationship type - Occupational and Environmental …oem.bmj.com/content/oemed/38/4/313.full.pdf · irregular opacities on their chest radiographs and 28 showed early changes ofprogressive

British Journal of Industrial Medicinie 1981 ;38:313-320

Relationship between type of simple coalworkers'pneumoconiosis and lung function. A nine-yearfollow-up study of subjects with small roundedopacitiesA W MUSK,* J E COTESt, CAROL BEVAN, AND M J CAMPBELL

From the MRC Pneumoconiosis Unit, Llandough Hospital, Penarth, S Glamorgan CF6 JXW, UK

ABSTRACT One hundred and twenty-five men who were identified in 1968 as having the simplepneumoconiosis of coalworkers were re-examined nine years later when their mean age was 59-6years. On both occasions the lung function and response to exercise were assessed. There was noevidence for progression of simple pneumoconiosis between the surveys, but 14 had developed smallirregular opacities on their chest radiographs and 28 showed early changes of progressive massivefibrosis (PMF). After allowing for the effects of smoking and of exposure to coal dust, subjects withboth p and r types of simple pneumoconiosis exhibited a reduced transfer factor compared withsubjects having q-type opacities; subjects with r-type opacities also showed an increased pulmonaryelastic recoil pressure. The presence of irregular opacities, independent of rounded opacities, was

associated with a low transfer factor and decreased slope of phase III of the single breath oxygentest. Subjects who developed PMF between 1968 and 1977 had p or r opacities more often than qopacities: these subjects had an increased pulmonary elastic recoil pressure. The development ofPMF was also associated with physiological evidence of airways obstruction. The changes insubjects with r opacities are consistent with the presence of space occupying lesions that mayprogress to PMF. Subjects with p opacities have physiological evidence of emphysema as do some

subjects with established PMF. Irregular opacities may reflect the presence of both emphysema anddiffuse fibrosis. There is need for more morbid anatomical evidence on the underlying pathology.

Previous studies of simple pneumoconiosis of coal-workersl 2 have shown that the pulmonary functionreflects the type of radiographic opacity; subjectswith pinhead (p) opacities have a lower gas transfercapability than subjects with micronodular (m or q)or nodular (n or r) opacities.3 This may result fromfocal emphysema or interstitial fibrosis associatedwith cystic or honeycomb change developing insubjects with p opacities.1 No other relationshipbetween radiographic type of simple pneumo-coniosis and pulmonary function has been foundconsistently. It has not even been possible to showabnormality for conventional tests of pulmonary

* Fellow in clinical sciences (epidemiology), National Healthand Medical Research Council of Australia. Present address:Sir Charles Gairdner Hospital, Nedlands, Western Australia,6009.tPresent address: University Department of OccupationalHealth and Hygiene, Newcastle upon Tyne.

Received 2 December 1980Accepted 20 January 1981

function in subjects with type "A" large opacities.4To investigate further the relation between type of

radiographic opacity and pulmonary function, wehave followed up a group of subjects first studied in19681 after a nine year interval. This paper docu-ments the longitudinal changes in pulmonaryfunction and radiographic appearance and looks forfunctional evidence of differences in pulmonarypathology between radiographic types. The factorscontributing to the clinical grade of breathlessness inthe same subjects is reported elsewhere.5

Subjects

In 1968 150 subjects were identified as having simplecoalworkers' pneumoconiosis after routine chestradiography by the National Coal Board; 125 ofthem participated in a study of the relationshipbetween radiographic type and pulmonary function.Of the 77 subjects with the greatest profusion of smallopacities, the 41 with predominantly p opacities hada lower transfer factor per unit alveolar volume and a

313

on 14 May 2018 by guest. P

rotected by copyright.http://oem

.bmj.com

/B

r J Ind Med: first published as 10.1136/oem

.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

Musk, Cotes, Bevan, and Campbell

more compliant lung than the 36 subjects withpredominantly micronodular (m or q) or nodular(n or r) opacities.' In 1977 all 125 subjects weretraced; 10 had died and 1 5 were invited to participatein a follow-up study. Four subjects refused to takepart, 22 agreed only to answer the respiratoryquestionnaire and perform spirometry at home, and89 attended at the pneumoconiosis unit for detailedstudies. Some were considered unfit and somerefused to participate in particular tests: the numberof participants is indicated in the tables of results.Satisfactory chest radiographs were obtained for 87subjects. Of the 10 men who died between the twosurveys, one died from malignant disease and onefrom trauma. The other deaths were equally dividedbetween cardiovascular and respiratory causes.

Methods

QUESTIONNAIREThe British Medical Research Council questionnaireon respiratory symptoms and smoking habits and afull occupational history was completed by allparticipants. Grading of breathlessness and ofbronchitis was according to the BMRC instructionbooklet.6

PULMONARY FUNCTIONForced expiratory volume in one second (FEV1),forced vital capacity (FVC), and maximal expiratoryflow volume (MEFV) curves were performed on adigital bellows spirometer.7

Total lung capacity (TLC), vital capcity (VC), andresidual volume (RV) were measured by the closedcircuit helium dilution method. Transfer factor forthe lung for carbon monoxide (Tl), multiple breathhelium dilution alveolar volumes (VA), and transfercoefficient (Kco = Tl/VA) were measured by themethod of Ogilvie et at8 on a Resparameter Mark IV(PK Morgan). Diffusing capacity of the pulmonaryalveolar membrane (DM) and capillary blood volume(Vc)9 were calculated by estimating TI after breathing100%02.4Thoracic gas volume and airways resistance (Raw)

by the panting technique'0 were measured in aconstant volume body plethysmograph" to derivespecific airway conductance (sGaw).Transpulmonary pressure was measured using a

10 cm latex balloon of circumference 3 5 cm con-taining 0-4 ml of air and connected to a Mercurypressure transducer (PM6) by a 100 cm polyethylenetube (id 1 mm) using the technique of Milic-Emili etal.'2 Maximal recoil pressure was taken as the meanof the three highest measurements of four or fiveseparate inflations to TLC. Static e,xpiratory volume-transpulmonary pressure curves were recorded

during interrupted expiration from TLC.13 Recoilpressure was measured at 50% VC (RP5o), and onelitre below TLC (RP1L), maximal recoil pressure(RPmax) was also recorded. Pulmonary compliance(CE) was taken as the slope of the volume pressurecurve at one litre above FRC.Pulmonary conductance-elastic recoil relation-

ships were measured by the method of Colebatch etal,14 flow being recorded on a Fleisch pneumo-tachograph No 3. Maximal expiratory flow volume(MEFV) curves were also recorded from the bodybox that was converted to measure volume change byintegration of the signal from a screen pneumo-tachograph mounted in its roof. These MEFV curveswere used to construct maximal expiratory flow-transpulmonary pressure curves and to derive ameasure of upstream resistance (Rus) at 50% VC.

Exercise was performed on a Lanooy cycleergometer. The work load was incrementallyincreased by 10 watts per min until a nominal 120watts (1969) or 80 watts (1978) was reached or untilthe subject stopped because of breathlessness orother discomfort. On two occasions in 1978 exercisewas curtailed because of ST-segment changes on theelectrocardiogram. Due to the calibration of theergometer possibly changing between the twosurveys the cardiorespiratory responses were relatedto the physiological load as assessed by the uptake ofoxygen and not to the indicated mechanical load.Minute ventilation (VE) was measured with a dry gasmeter15 and tidal volume by integration of a Mercurypneumotachograph signal.'6 Cardiac frequency wasrecorded from lead V5 of an electrocardiogram. Theventilation and cardiac frequencies at an oxygenuptake of 45 mmol/min (1-0 1/min) (VE45 and fc4s)were obtained by interpolation.4

Nitrogen index (N21) which was the slope of phaseIII of the single breath oxygen test was measuredusing a modification of Fowler's method17; nitrogenconcentration being monitored on a mass spectro-meter (MS4, Centronics).Body weight was measured on a balance scale and

stature with a Harpenden stadiometer.4

COAL DUST EXPOSUREIndices of exposure to coal dust were calculatedusing the detailed occupational history and assigningthe various job descriptions to a five-point scale ofseverity of exposure to coal dust: (a) total years inthe coal mining industry (TOTYR), (b) total dustexposure (TOTXP), (c) accumulated years in the coalmining industry (ACCUYR), (d) accumulated dustexposure (ACCUXP), and (e) discounted dustexposure (DISXP). For example, suppose that aman's history in coal mining up to the present is niyears at dust level xi, followed by n2 years at dust

314



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

Relationship between type of simple coalworkers' pneumoconiosis and lutigfunction3

level X2. Then:(a) TOTYR = ni + n2(b) TOTXP = nfxi + n2X2(c) ACCUYR = (1+ 2 + ... + n2) +[(n2 + ...

+ (n2 + nl)](d) ACCUXP = (X2 + 2X2 + ... + n2X2) +

[(n2 + 1)xi + . (n2 + nli)X](e) DISXP = X2(1 - exp(-Bn2)) +

xi exp(-Bn2) (1 - exp(-Bnl)Discounted exposure18 assumes that the lung heals

(or fibroses) at a rate B, proportional to the currentamount of damage. Thus a heavy exposure may haveless effect on present lung function if it happened inthe distant past than if it happened recently. Theconstant B is estimated by trial and error-that is,if the lung takes five years to repair half the damagethen B = loge 2/5.

It was found that TOTXP and TOTYR showedthe highest negative correlation with level of FEVand with radiographic category, and these indiceswere used in the subsequent analyses.

CHEST RADIOGRAPHY

Standard full size posteroanterior chest radiographswere obtained. Focus-film distance was six feet, andthe exposure used was 70 KV, 200-300 mA for0 3-04 s.

The profusions of small rounded and irregularopacities3 were read for 1978 and re-read for 1968 byone expert observer who had not seen the filmspreviously. The films were read side by side.

STATISTICAL PROCEDURES

The association between pulmonary function andvarious radiological changes such as size and shapeof small opacities was examined by multiple regres-sion analysis'9 using the GENSTAT computerprogram20 to allow for any differences in age, height,and smoking habits between radiographicallydetermined groups. For example, to examine the

association between pulmonary function and irregu-lar opacities we fitted an equation of the formy = a + b age + c height + d smo + e exsmo +

f irregThe variables smo, exsmo, and irreg are dummyvariables, taking the value zero except that smo = Iif the subject is a smoker, exsmo = 1 if the subject isan ex-smoker, and irreg = 1 if the radiograph showsirregular opacities. The coefficients a, b, c, d, e, and fare determined by multiple linear regression,together with their standard errors. The significance ofa particular term is computed making the assumptionthat the ratio of an estimate to its standard errorfollows an approximate "t" distribution. The meanvalues in the tables are y = a + b (mean age) + c(mean height), where a, b, c, are the estimatedvalues of a, b, c in the above model and thus the yvalues are those predicted fornon-smokers.To examinewhether size (p, q, r) could account for the effectsfound for shape, firstly, table 4 was produced,showing no significant correlation between size andshape. Then two additional dummy variables wereadded to the above model. These were dump = 1 ifsubject has p-type opacities and dumr = 1 if thesubject has r-type opacities, and both are zero else-where. The significance of the irregular opacities wasnot materially changed by the addition of these twovariables, and similarly the significance of the sizeparameter was not changed compared with the modelthat contained dump and dumr but not irreg.

Results

RADIOGRAPHIC APPEARANCESFor subjects followed up in 1978 there was no radio-graphic progression of profusion of simple pneu-moconiosis since 1969 (table 1). Fourteen men werefound to have developed irregular opacities (table 2).Twelve developed ill-defined large opacities and 16progressed mainly from ill-defined to well-defined

Table I Progression of profusion of small opacities between surveys

Radiographic Radiographic category: 1978category:1969 1/0 1/1 1/2 2/1 2/2 2/3 3/2 3/3 Dead NA Total

1/0 I11/1 6 3 3 121/2 42/1 1 l 7 3 122/2 1 16 3 7 282/3 1 = 2 4 203/2 1 2 I 7 2 1 143/3 1 1 20 1 7 303/4 1 1NA 2 1 3Total 9 3 10 20 15 9 21 10 28 125

NA = Radiograph not available.

315



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

316

Table 2 Progression of irregular opacities betweensurveys

Radiographic Radiographic category: 1978category: _________1969 0 s t Dead NA Total

0 54 0 14 6 25 99s 1 2 0 0 0 3t 1 0 12 4 3 20NA I 0 2 0 0 3Total 57 2 28 10 28 125

NA = Radiograph not available.

lesions (table 3). Subjects who developed largeopacities were not recruited preferentially from thosewith the higher categories of simple pneumoconiosis.The cause of death in the 10 subjects who diedbetween surveys was unrelated to the type or extentof the rounded opacities present in 1969. The subjectswho were seen at home after declining to attend atthe laboratory were on average older than those whoattended but the two groups were otherwise similar.

PULMONARY FUNCTION, SMOKING, ANDDUST EXPOSUREPulmonary function was related to smoking historyand to exposure to coal dust (table 4). Subjects whowere cigarette smokers in 1978 had a significantlylower FEV1, FVC, and FEV/FVC and higher RV/TLC, while ex-smokers had a lower Tl and Kco andhigher RV/TLC compared with non-smokers. Totaldust exposure was significantly inversely related toFVC and RPmax.

SIMPLE PNEUMOCONIOSISIn 1978 the presence of p opacities was associatedwith significantly lower values for Tl and Kcocompared with subjects exhibiting q opacities (table5); there was also a tendency toward a higher levelof CE.

Subjects with r opacities in 1978 also had a lowermean Kco compared with those having q opacities:additionally, they had a higher RP1L and RP5o and a


Table 4 Association of exposure and smoking onpulmonary function* 1978

Regression Current Ex-smokers+coefficient on total smokerstexposure(TOTXP)(yr)

FEV, (l) -0 0033 -053tt -0 30FVC (l) -0-0046t -0 44t -0-31FEV,/FVC(%) -0 0145 -7-39t -3-06TI (mmol/min/kPa) 0-0006 - 1.09 - 1-35tKco(mmol/min/kPa/l) 0-0002 -0-16 -0 20tTLC (l) 0-0012 -0-06 0-03RV (I) 0-0032 0-35 0-42RV/TLC (%) 0 0377 6-3t 6-4ttCE (l/kPa) -0-0002 -0 04 -0 04RPIL (kPa) -0-0207t 0-21 0-07RP50 (kPa) -0 0097 0 49 -0-01RPmax(kPa) -00510t 2 09 0 75sGaw (I/s/kPa) -0-0001 - 003 -0-01VE, (l/min) 0-0163 - 1-29 -0 73FC, (min-1) -0 0718 14 5 -1-40Rus (kPa/s) 0 00079 0-16 0 063N21 (%) -0-0098 -0-78 -0-62

*After correcting for the effect of age and height.t, ttSignificantly different from zero or non-smokers at respectively5 % and I % levels.+Mean effect compared with non-smokers. For example, currentsmokers have a deficit in FEV, of 0 53 1 compared with non-smokers.

tendency to lower CE. There were no differences inmagnitude of change in lung function between 1969and 1978 between subjects with the several types ofsimple pneumoconiosis except for a greater fall inRP5o in subjects with p opacities; there may havebeen a technical explanation for this (see discussion).

IRREGULAR OPACITIESSubjects with irregular opacities in 1978 were olderand taller than those without. They had a signifi-cantly reduced Kco and Tl and a lower nitrogenslope (table 6). These indices contributed significantlyto a discriminant function which distinguishedsubjects with irregular opacities from others withpneumoconiosis. The type of small rounded opacitiespresent in 1969 did not appear to be related to thesubsequent development of irregular opacities.

Table 3 Progression of large opacities between surveys

Radiographic Radiographic category: 1978category:1969 0 A(id) A B(id) B C Dead NA Total

0 45 10 2 9 23 89A(id) 3 L 7 3 1 2 3 26A 1 1 2 4B(id) 2 2BC 1NA I 1 1 3Total 49 17 7 6 4 4 10 28 125

id = Ill defined.NA = Radiograph not available.



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

Relationship between type of simple coalworkers' pneumoconiosis and lung function

Table 5 Association of type of small rounded opacitywith pulmonary function* 1978

p q r

No§ 19 53 12Age (yr) 58 5 59 5 60 0Ht (m) 1-70 1 67 1-68Total exposure (TOTXP) 118-5 120-8 132-6% smokers 53 53 58% ex-smokers 26 19 33FEV1 (1) 2 73 2-52 2-73FVC (1) 3-88 3-66 3-87FEV,/FVC (%) 704 68-0 70 0TI (mmol/min.kPa) 805tt 9 39 8-57Kco (mmol/min.kPa.1) 1l32tt 1-58 1 40tTLC (1) 2-26 6-23 6-40RV (1) 2 31 2-45 2-34RV/TLC (%) 367 38 9 36-2CE (1/kPa) 0-38 (16) 0 33 (46) 0 27 (10)RPIL (kPa) 7-26 (16) 7-11 (46) 8 76t (10)RP50 (kPa) 5-26 (16) 4-69 (46) 6-26tt (10)RPmax (kPa) 14-7 (16) 16 9 (46) 18 1 (10)sGaw (1/s/kPa) 14tt 1.1 1.1VE, (1/min) 33 9 (12) 31-7 (40) 31-6 (7)FC, (min-]) 102-1 (12) 99-8 (40) 95-3 (7)Rus (kPa/s) 0 23 (15) 0-23 (42) 0-27 (10)N.1 (%) 1-14 (16) 1 79 (49) 2 19 (12)

*After correcting for the effects of age, height, and smoking category.§Three subjects classified as irregular only were not included in thistable. Smaller numbers of subjects are shown in parentheses.t,t tSignificantly different from the q opacity group at respectively 5%and I % levels.

Table 6 Association of irregular opacities withpulmonary function* 1978

Irregular Irregularopacities absent opacities present

No 57 30Age (yr) 58-3 62-1Ht (m) 1 67 1 70Total exposure (TOTXP) 1 18 8 130-2% smokers 56 48% ex-smokers 21 33FEVI (1) 2 58 2-56FVC (1) 3 71 3-74FEV,/FVC (%) 68-8 67-8TI (mmol/min.kPa) 9 54 8-32tKco (mmol/min.kPa.l) 1-58 1-42t;TLC (1) 6 30 6 18RV (1) 2-49 2-30RV/TLC(%) 39 2 36-8CF (1/kPa) 0-336 (55) 0-329 (20)RPIL (kPa) 7 08 (55) 7 41 (20)RP,, (kPa) 4 71 (55) 5 03 (20)RPmax (kPa) 16-0 (55) 17 9 (20)sGaw (1/s.kPa) 1 16 1.19V,E (1/min) 31 6 (40) 32-2 (20)FC, (min-I) 97-2 (40) 105-7 (20)Rus (kPa/s) 0-29 (40) 0 11 (20)N21(%) 49 2 31

*After correcting for the effects of age, height, and smoking category.t,tt Significantly different from the "irregular opacities absent" groupat respectively 5 % and 1 % levels.

Subjects with irregular opacities were not unusual intheir smoking habits or the extent to which theirscore for bronchitis or breathlessness increasedbetween surveys. The rate of decline of TI and Kcotended to be greater in subjects who developed

Table 7 Pulmonary function in 1969 in relation to thesubsequent development of large opacities

Large Large Largeopacities opacities opacitiespresent 1969 present 1978 absent 1969and 1978 absent 1969 and 1978

No 24 12 46Age (yr) 53-1 51 3 51-5Total exposure (TOTXP) 132-1 119-6 113 8FEV, (1) 2-34 2-46 2 58FVC (1) 3 56 3-77 3-70FEV,/FVC 65 80 69-75 64-09TI (mmol/min.kPa) 8-36 9 12 8-93Kco (TI/VA) 1 41 1-41 1-49TLC (He) (I) 6 18 6-72 6-22RV (1) 2-33 2-64 2-22CE (1/kPa) 0-355 0-232 0-341RPIL (kPa) 5 65t 8-38t 6-94RP55(kPa) 3-44 4-78 4-02sGaw (1/s/kPa) 1 78t 1 64tt 2-38VE, (1/min) 34-80 32-74 34 56FC, (min-I) 104-5 96-40 101-3

Statistical significance of difference from subjects with no largeopacities in 1969 or 1978 t p < 0-05 tt p < 0-01. For symbolsand abbreviations see text.

Table 8 Type of small opacity and development oflarge opacities

p q r Total

Large opacity developed 5 4 3 12Large opacity did not develop 8 34 3 45Total 13 38 6 > 57*

*Remaining radiographs were considered to have large opacities in1969. Result shows that significantly fewer subjects with q opacitiesdeveloped large opacities, compared with p and r (x2, = 7 93,p < 002).

Table 9 Relationship between type and shape of smallopacities in 1978

Rounded

0 p q r Total

Irregular absent 0 14 8 35 57Irregular present 3 5 4 18 30Total 3 19 12 53 87

For the 84 radiographs with small rounded opacities, contingencytable analysis gives X22 = 0-38, p > 01-that is, no correlationbetween size and shape of small opacity.

irregular opacities between surveys compared withthose who did not, but the difference did notapproach statistical significance.

PROGRESSIVE MASSIVE FIBROSISSubjects who had large opacities in 1969 or whosubsequently developed large opacities had signifi-cantly lower mean values for sGaw than the subjectswith simple pneumoconiosis in 1978 (table 7).Subjects with large opacities present in 1969 had asignificantly lower mean RP1L and subjects whodeveloped large opacities between 1969 and 1978 asignificantly higher RP1L compared with subjects

317



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/


without large opacities in 1978. The presence of largeopacities categories B and C in 1978 was associatedwith a significantly lower mean FEV1, FEV,/FVC,and CE and a tendency to lower sGaw and Ticompared with the other subjects. The pulmonaryfunction of subjects with category A large opacitiesdid not differ significantly from that of subjects withsimple pneumoconiosis alone. The subjects with p orr opacities showed a greater attack rate ofPMF thandid the subjects with q opacities (table 8). Therewas no association, however, between the type ofsimple pneumoconiosis and the presence or absenceof PMF in either 1969 or 1978 (table 9).

Discussion

The coal miners in this study, who were all workingin 1969, were then considered by three readers to havewell-established radiographic simple pneumoconiosiswithout PMF or conspicuous irregular opacities.Among these subjects those with predominant p-typeopacities had some of the physiological features ofemphysema, including a reduced Kco and increasedstatic lung compliance. Subsequently one of thesubjects developed the features of cystic lung, andthis observation led to the present follow-up study.The methods used in the two studies were similar

but the operators were different. This was probablynot important except in the case of the recoilpressure, where the technique for reading the oscillo-scope image used in 1969 was such as to lead tosystematic underestimation; CE was probably notaffected. In addition, in 1978 the radiographs for1969 and 1978 were read side by side by one highlyexperienced observer who had not seen the filmspreviously. This process led to the reclassification asPMF of 33 of the 1969 films previously read as simplepneumoconiosis; 28 were read as ill-defined largeopacities, four as category A, and one as category C.On the second occasion the films were read for smallirregular opacities and 23 cases were so identified,although in general the lesions were not extensive;this was to be expected as in the initial selection ofsubjects in 1969 those whose radiographs showed apronounced reticular pattern were excluded.The mortality experience of 10 deaths in the

subsequent nine years among the 125 men seen in1969 is unexceptional, but it is of interest that threewere read as having irregular opacities and of these,two died a respiratory death. The 22 subjects seen athome were older but were similar to those who werestudied in detail in all other respects includingventilatory capacity and respiratory symptoms. Thelapse rate was only 3-2%. Thus the present findingsaccurately reflect the status in 1978 of the subjectsseen in 1969; whether or not the findings are typical

of all men with advanced simple pneumoconiosis inSouth Wales can be established only by study ofcomplete populations as has been done by Cochraneet al.21The present results show the expected increased

airway obstruction in smokers4 and of FVC inproportion to exposure to coal dust.22 The ex-smokers also had impaired lung function, which mayhave contributed to their stopping smoking. Theseassociations as well as those with age, stature, andbronchitis were taken into account when consideringthe relationship of lung function to radiographiccategory.The finding that among men with simple pneu-

moconiosis those with p-type opacities had a lowerTl and Kco and a tendency towards a highercompliance compared with men having q opacities isconsistent with the earlier studies.1 23 The exerciseventilation was also rather higher than in the qcases, but unlike in a previous investigation24 thisdifference was not significant. In addition, comparedwith 1969 and after allowing for the systematicdifference in recoil pressure between the two surveys,the results of the follow-up study showed a sig-nificantly greater decline in recoil pressure in the pcases. The previous result was interpreted as evidencefor focal emphysema and the present findings areconsistent with this view. There is an urgent need forinformation on the morbid anatomy of the lung inthese cases; a procedure for its collection has beenset up and material is now accumulating.Among men with r opacities the reduced Kco

associated with an increase in recoil pressure and atendency towards a reduction in lung compliance isevidence that the lung function is more affected bythe occupational exposure than in men with qopacities. The pattern and extent of abnormality issuggestive of mild diffuse fibrosis or space occupyinglesions. The absence of changes in exercise ventilationor in total lung capacity militate against the abnor-mality being of functional significance. Its presence,however, suggests that the different radiographicabnormalities of simple pneumoconiosis reflectunderlying structural differences which, at theextremes, range from very small to largish nodules ofaccumulated dust and from diffuse focal emphysemato diffuse fibrosis. These abnormalities to someextent coexist and their physiological features over-lap. Thus the differences that have been observedmay be of greater consequence than their smallmagnitude would suggest; they may also reflect inpart the initial condition of the lung. In addition theyare associated with different propensities fordeveloping PMF. The explanation of this findingrequires a greater understanding of the mechanism ofdevelopment of PMF than is at present available. It

318



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

Relationship between type of simple coalworkers' pneumoconiosis and lung function

will need to take into account that while the attackrates differed between the radiographic types ofsimple pneumoconiosis the distribution of typesamong the subjects with PMF was similar to that formen with simple pneumoconiosis. The present studyconfirms the absence of physiological abnormality inmen with A shadows other than that associated withsmall opacities.4 Among those with B and C opacitiesin 1978 there was a significant degree of airwaynarrowing, which in 1969 also extended to those whosubsequently developed large opacities between thetwo surveys. The presence of large opacities wasassociated with changes in lung elasticity includingan increased recoil pressure (1969) and reduced lungcompliance (1978); the transfer factor was some-what reduced. The latter features are consistent withloss of lung tissue secondary to the development ofspace occupying lesions; the former may reflect anassociated distortion and narrowing of the airwayspreceding the respiratory symptoms that are afeature of the established condition.Men with irregular opacities were older and taller

than the others. After allowing for this and forchanges in lung function associated with pneumo-coniosis and smoking they had a reduced transferfactor and Kco. This finding, which is evidence forloss of functional lung tissue, was predicted in theearlier study' where it was noted that the reduction intransfer factor with p-type simple pneumoconiosisobserved by Billiet and colleagues was greater thanfor the present subjects; the two studies differed inthat the formerincluded men whoseradiographs wereread as having profuse irregular opacities-whereasthe presence of extensive irregularities was anindication for exclusion from entry to the presentinvestigation. In addition, in the Belgian study theirregular opacities appeared to be more prevalentamong men with p-type opacities. This associationwas not observed in the present study. Nor was thereinteraction between irregular opacities and smokingleading to increased airways obstruction as observedby Amandos et al.25 The decreased nitrogen index inthose with irregular opacities may be due to diffusefibrosis widening the small lung airways. However,there were no clear-cut parallel changes in total lungcapacity, compliance, recoil pressure, and upstreamresistance, which suggests the presence of additionalemphysema and is consistent with a recent pre-liminary study of the underlying pathology.26 Thereis need for more information before the status ofirregular opacities can be established with certainty.

We are indebted to many colleagues at the MRCPneumoconiosis Unit for their help in this studyincluding in particular Dr J C Gilson, who read thechest radiographs taken by Miss S Latham; Miss C

1*

Exall, who contacted some of the subjects; Mr M JSaunders, Mr G R Johnson, Mrs I Ashton, Mrs J MRobson, and Mrs G Collins, who made some of thephysiological measurements; and Mrs P E J Hardingand Mrs E M Humphries who typed the manuscript.Requests for reprints should be addressed to Mrs Bevan.

ReferencesCotes JE, Deivanayagam CN, Field GB, Billiet L. Relation

between type of simple pneumoconiosis (p or m) andlung function. In: Walton WH, ed. Inhaled particles III.Old Woking: Unwin Bros, 1971:633-43.

Seaton A, Lapp NL, Morgan WKC. Relationship ofpulmonary impairment in simple coalworkers' pneu-moconiosis to type of radiographic opacity. Br J IndMed 1972 ;29 :50-5.

3 International Union against Cancer Committee. UICC/Cincinnati classification of the radiographic appearancesof pneumoconiosis. A comparative study by the UICCCommittee. Chest 1970;58:57-67.

'Cotes JE. Lung function. Assessment and application inmedicine. 4th ed. Oxford: Blackwell, 1979.

Musk AW, Bevan C, Campbell MJ, Cotes JE. Factorscontributing to the clinical grade of breathlessness incoalworkers' pneumoconiosis. Bull Eur PhysiopatholRespir 1979 ;15:343-53.

6 Medical Research Council Committee on Research intoChronic Bronchitis. Instructions for use of the ques-tionnaire on respiratory symptoms. Dawlish, Devon:WJ Holman, 1966.

7McDermott M, McDermott TJ. Digital incrementaltechniques applied to spirometry. Proc R Soc Med 1977;70:169-71.

8Ogilvie CM, Forster RE, Blakemore WS, Morton JW. Astandardized breath holding technique for the clinicalmeasurement of the diffusing capacity of the lung forcarbon monoxide. J Clin Invest 1957;36:1-17.

Roughton FJW, Forster RE. Relative importance ofdiffusion and chemical reaction rates in determining rateof exchange of gases in the human lung. J Appl Physiol1957;11 :290-302.

10 Dubois AB, Botelho SY, Comroe JH, Jr. A new method formeasuring airway resistance in man using a bodyplethysmograph. Values in normal subjects and inpatients with respiratory disease. J Clin Invest 1956;35:327-35.

Reynolds JA, McKerrow CB. A multiplex cathode-ray-tubedisplay with digital readout for a body plethysmograph.Med Biol Eng 1973 ;11 :268-74.

12 Milic-Emili J, Mead J, Turner JM, Glauser EM. Improvedtechnique for estimating pleural pressure from eso-phageal balloons. J Appl Physiol 1964;19:207- 11.

13 Hart A, McKerrow CB, Reynolds JA. A method of usingan x-y recorder in measuring the lung compliance.J Physiol (Lond) 1966;184:50P-2P.

14 Colebatch HJH, Finucane KE, Smith MM. Pulmonaryconductance and elastic recoil relationships in asthmaand emphysema. J Appl Physiol 1973;34:143-53.

15 Saunders MJ, James PJ. Digital respiratory rate andventilation recorder. Med Biol Eng Comput 1978;16:337-8.

16 McKerrow CB, Reynolds JA. A versatile respiratoryintegrator. J Physiol (Lond) 1968 ;200:13-5P.

17 Comroe JH, Jr, Fowler WS. Detection of uneven venti-lation during a single breath of 02. Am J Med 1951;10:408-13.

16 British Thoraic and Tuberculosis Association Committee.

319



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

320

Opportunist mycobacterial pulmonary infection andoccupational dust exposure. An investigation in Englandand Wales. Tubercle 1975;56:295-309.

Kendal MG. Multivariate analysis. London: Ch Griffin,1975.

2o Alvey NG, Banfield CF, Baxter RI, et al. A generalstatistical program. Harpenden: Statistics Department,Rothamsted Experimental Station, 1977.

21 Cochrane AL, Haley TJL, Moore F, Hole D. The mortalityof men in the Rhondda Fach. Br J Ind Med 1979;36:15-22.

23 Rogan JM, Attfield MD, Jacobsen M, Rae S, Walker DD,Walton WH. Role of dust in the working environment indevelopment of chronic bronchitis in British coalminers.Br J Ind Med 1973;30:217-26.


23 Lyons JP, Clarke WG, Hall AM, Cotes JE. Transfer factor(diffusing capacity) for the lung in simple pneumoconiosisof coal workers. Br MedJ 1967;iv:772-4.

24 Cotes JE, Field GB. Lung gas exchange in simple pneu-moconiosis of coal workers. Br J Ind Med 1972;29:268-73.

25 Amandos HE, Lapp NL, Jacobsen C, Reger RB. Signi-ficance of irregular small opacities in radiographs ofcoalminers. Br J Ind Med 1976;33:13-7.

26 Cockcroft AE, Wagner JC, Seal RME, Lyons JP,Campbell MJ. Irregular opacities in coal workers'pneumoconiosis-correlation with pulmonary functionand pathology. In: Walton WH, ed. Inhaledparticles V.Old Woking: Unwin Bros, (in press).



.bmj.com

/B


.38.4.313 on 1 Novem

ber 1981. Dow

nloaded from

http://oem.bmj.com/

Documents

Relationship type - Occupational and Environmental …oem.bmj.com/content/oemed/38/4/313.full.pdf · irregular opacities on their chest radiographs and 28 showed early changes ofprogressive