International Archives of Int Arch Occup Environ Hlth
(ccutImnw
37,249-264 (1976)
Imd Enlvironnenlal Iiealth ©
by Springer-Verlag 1976
Angina Pectoris, Electrocardiographic Findings and Blood Pressure inFinnish and Japanese Workers Exposed to Carbon Disulfide MATTI TOLONEN 1 *, SVEN HERNBERG', CLAES-HENRIK NORDMAN 1 , SHIGERU GOTO 2 , KANJI SUGIMOTO 2, and TOSHIO BABA3 1 Institute of Occupational Health, Helsinki, Finland 2 Department of Hygiene, 3 Asahi Kasei Co
Summary
Medical School, Osaka University, Osaka, Japan
Ltd , Nobeoka, Japan
The response to a standardized angina and infarction questionnaire,
the occurrence of coded resting and postexercise ECG findings suggestive of coronary heart disease (CHD), and blood pressure were studied among 417 male Japanese and 237 Finnish workers exposed occupationally to carbon disulfide (C52 ) and their controls, posure
391 Japanese and 233 Finnish men without such ex-
All of the subjects were aged 35 to 54 years
Among the Japanese
subjects only seven exposed and one unexposed worker had a history of angina; typical angina was present in two exposed and in none of the unexposed men; and one had a history of possible myocardial infarction
In the Finnish ex-
posed and unexposed groups the prevalence were 15 and 10% for total angina, and 4 and 4% for typical angina, respectively
No impressive differences
emerged in the prevalences of "coronary" ECG items between the exposed and unexposed groups
The presence of "coronary" ECG findings was no more fre-
quent in those with a history of angina than in those workers without such findings
None of the exposed and unexposed Japanese subjects with "coronary"
ECG changes gave history of angina or infarction
The
"coronary" ECG preva-
lences for the Finnish exposed and unexposed men were 30 and 24%
If a his-
tory of angina together with "coronary" ECG abnormalities are taken as evidence of probable CHD, the total prevalence among the Japanese was O % for both the exposed and the unexposed group; respectively
Smoking history, obesity,
differences in the Japanese groups
and among the Finns, 5 and 2%,
and blood pressure showed no marked
The diastolic and systolic blood press-
ure were significantly higher among the exposed Finnish workers than among the controls
The study yielded no evidence for an increased occurrence of
the examined parameters among the Japanese workers exposed to carbon disulfide,
whereas the exposure seemed causally associated with excess angina
and high blood pressure among the Finns
The potential CHD induced by C 52
seemed to be undetectable by means of electrocardiography. Key words: Carbon disulfide Minnesota code
Angina pectoris
Exercise electrocardiography-
Coronary heart disease.
Address for offprint requests:
Institute of Occupational Health, Haartmanin-
katu 1, FIN-00290 Helsinki 29,
Finland
249
INTRODUCTION Carbon disulfide (C52) has been recognized as a toxic factor for coronary heart disease (CHD) among chronically exposed workers, particularly in the viscose rayon industry (Tiller et al , 1968 ; Mow S, 1971 ; Hernberg et al , 1970, 1973 ; Tolonen et al , 1975). The likelihood of a genuinely causal association is great since the effect has been shown to be consistent in several investigations and plausible explanations as to the mechanism of action exist (Hernberg et al , 1973) The excessive incidence of coronary deaths among C 52 workers has stimulated further studies on the relationship between CHD and C 52 , but separation of the effect of C 52 from that of confounding factors has been a major problem Furthermore, unbiased determination of the various manifestations of CHD has been an obstacle to correct inference, mainly because reliable means for the detection of the disease in vivo have not yet been developed. In addition to the history of subjective symptoms suggestive of CHD the ECG examination has been widely advocated as an indicator of coronary insufficiency In the past several years some studies have focused on the relationship between exposure to C52 and ECG abnormalities suggestive of CHD (Goto and Hotta, 1967 ; Hernberg et al , 1970 ; Cirla et al , 1972 ; Tomasini et al , 1972 ; Tolonen et al , 1975) Unfortunately the selection of subjects, the type and degree of excercise, if employed, and the criteria used to interpret the EC Gs have varied greatly Consequently, it is not possible to deduce whether the contradictory results of these studies stem from population or methodological differences Perhaps the greatest source of confusion comes from the interpretation of ECG findings, because, first, to date, no criteria have commanded universal acceptance as diagnostic means and, second, the interpretation of the ECG tracings is subject to gross inter and intraobserver variation (Davies, 1958 ; Acheson, 1960 ; Blackburn and a technical group, 1968). A common language is needed among investigators studying the association between CHD and C52 ; this need prompted us to carry out a collaborative study on the epidemiology of C 52 induced cardiovascular disease We examined the blood pressure, the prevalence of angina pectoris, and the ECG findings suggestive of CHD among a group of male Japanese workers exposed to C 52 and unexposed men These results are compared with those of a Finnish series and their unexposed controls.
MATERIALS AND METHODS The study comprised two sets of exposed and unexposed men, one Japanese and the other Finnish The Japanese groups were formed of 417 exposed and 391 unexposed male workers 35 to 54 years of
250
age During the examination all the subjects were employed either in a viscose rayon plant (the exposed group) or a cuprammonium rayon plant (the control group) Both Japanese groups were unselected with regard to CHD or other conditions. The Finnish subjects belonged to an exposed or an unexposed cohort, 343 men each, formed and examined in 1967 1968 as described previously by Hernberg and coworkers (Hernberg et al , 1970) We analyzed the data collected at that time for all those 237 exposed and 233 unexposed men, aged 35 to 54 years, who were all presently employed either by the viscose rayon plant (the exposed group) or the paper mill (the control group) at the time of the examination. We attempted to reduce measurement variability and to minimize observer error in order to maintain comparability between the two ethnic populations, and therefore all the methods applied in Japan and in Finland corresponded exactly A detailed description has already been published (Hernberg et al , 1970), but a brief summary may be useful. The history of angina pectoris was elicited with Rose's questionnaire (Rose, 1962 ; World Health Organization, 1963), which allows for the classification of reported symptoms according to the severity and probability of coronary etiology. The reproducibility of the questionnaire has been previously tested and found satisfactory for use in population studies (Rose, 1968 ; Milne et al , 1971 ; Zeiner-Henriksen, 1972). In addition to the indices of CHD, i e , angina pectoris symptoms and ECG abnormalities, the investigation included measures of other variables that previous experience suggests to be major risk factors for CHD, namely, smoking habits, obesity and blood pressure Smoking habits were clarified by means of a questionnaire, the result of which appear in Table 1. There were more Finnish nonsmokers than Japanese but for a within-study comparison the differences were not considered to cause any bias Relative body weight (obesity index) was calculated with the following formula: Obesity Index = Present body weight (kg) Ideal body weight (kg)
100
Ideal body weight was determined as 0 9 x (height 100); the height was expressed in centimeters The relative body weight appeared to be the same in the respective exposed and unexposed groups within-studies. Blood pressure was determined according to a standard procedure with a mercury column, equipped with a wrap-around cuff (14 x 65 cm), and a stethoscope The measurements were made, after the subjects had rested for at least 15 min by the same observer within studies. The ECG response to single-load submaximal exercise was determined during bicycle ergometry in 216 Finnish and 404 Japa-
251
Table 1 Prevalences (%) of cigarette smokers and nonsmokers among the Japanese and Finnish workers, aged 35 to 54 years Cigarettes per day
Japanese
Finnish
Exposed N = 417
Unexposed N = 391
Exposed N = 237
Unexposed N = 233
0 or quit
32
29
44
50
1
19
50
36
36
33
>
20
18
35
20
17
nese exposed and in 221 Finnish and 380 Japanese unexposed men. The work load was set according to age (and for a few individuals according to estimated fitness) as 150 W for persons less than 49 years and 100 W for subjects 50 to 54 years Because of a medical or physiological contraindication to a stress test a resting ECG was recorded for the rest of the subjects. The ECG tracings were coded by the Minnesota ECG code (Rose and Blackburn, 1968) with the exception that the Finnish system for classifying ST segment changes was employed (Punsar et al., 1968) The changes with > 0 5 mm sagging or horizontal ST segment depression, accepted as being suggestive of myocardial ischemia, were considered The Japanese records were coded in Finland independently by two experienced technicians, and where the results disagreed the tracing was reexamined and an agreed coding supplied. The rejection criteria in the preentry medical examination in the Japanese and Finnish industries concerned had not differed considerably with regard to CHD or its known risk factors when the subjects were recruited for the study.
Toxic Environment The levels of exposure to C 52 in the Finnish viscose rayon plant have been described several times previously (Hernberg et al , 1970 ; Raitta et al , 1974 ; Tolonen et al , 1975) In the 1950s the C 52 +H 2S levels varied between 20 and 60 ppm; in the 1960s, between 10 and 30 ppm; and in 1970S between 5 and 10 ppm. The C 52 concentrations in the Japanese plant are illustrated by Figures 1 and 2 In the light of the overall exposure levels the work conditions are roughly comparable to the Finnish ones. The individual exposure of the Japanese men was classified as either "high" or "low" An exposure index was calculated as follows: the number of months spent in "high" exposure was multi-
252
E 0. a
c
.2 0 0
C
a U
Fig 1 Time-weighted concentration of C52 in the air of rayon filament plant; N = number of samples per year; N = total number of samples 1948-1955, 1956-1965 and 1966-1972 Spinning department 1st room 2nd room 3rd room
n = 174 N =
n = N = n = N=
343 773
8 493 1983 12
o o
o
n = 219 N =
o
448
1958
770 5676
n = 414
N =
947 n = 251 N = 6126
n = 510
n = 310
n = 310
N=
1045 5966
N = N =
1972
5969 2108
6371 1045
6203
E 15
-
0/ 1966 1967 Fig 2
1968 1969 1970 1971 1972
Time-weighted concentration of C52 in the air of plants of rayon filament and C52 production; N = number of samples per year; N = total number of samples 1966-1972 Xanthation o-o N = 34 427, N = 1571 ; Ripening o
o
N = 51
696,
N = 1936 ; C 52 production e
N = 13
34, N =
106
plied by three, and the time (in months) spent in "low" exposure as such equaled the index Thus the index was weighted towards "high" exposure. Diagnostic Criteria Chest Pain Symptoms
The replies elicited with the standardized
questionnaire were considered indicative of angina if a subject reported a) any pain or discomfort in his chest when walking up-
253
Table 2 Prevalences (%) of angina and rate differences (RD) (%) in Japanese and Finnish exposed and unexposed workers, aged 35 to 54 years Classification of angina
Finnish workers
Japanese workers Exposed N = 417
Typical Probable
0 5 O 2
Possible
1 O
Total
17
Unexposed N = 391
RD
Exposed N = 237
Unexposed N = 233
RD
O 5 O 2
4 5
4 2
O 3
O 3
O 7
6
4
2
O 3
14
15
10
5
hill or when hurrying on level ground, and b) that the pain forced him stop or slow down, and c) that the pain related to walking localized itself in the sternal area or simultaneously on the left side of the chest or the left arm Typical angina was judged as present when chest pain was felt not only when walking uphill or when hurrying on level ground but also when walking at an ordinary pace on level ground and the site involved the sternum or the left arm Angina was classified as probable if the pain occurred when hurrying on level ground or when walking uphill Chest pains associated with walking but not fulfilling the above criteria were classified as possible angina, and chest pain occurring when standing still or sitting was not considered as angina. Severe pain across the front of the chest lasting for half an hour or more was regarded as indicative of myocardial infarction. We analyzed the prevalence of isolated Minnesota codes of the resting EC Gs accepted as indicative of myocardial ischemia as follows: Minnesota codes 1 1-3 (Q-wave changes) Minnesota codes 4 1-3 (ST-segment depressions) Minnesota codes 5 1-3 (T inversions). The findings coded from the postexercise ECG were "ischemic" postexercise ST depression (Minnesota codes 11 1-3 or 4 4 + 11 5), postexercise T inversion (Minnesota code 12 1-3), and change from no coded arrhythmia at rest to any reportable arrhythmia postexercise (Minnesota code 15 1) Only individuals with a completed or almost completed exercise test were taken into account in the calculation of the prevalence of the postexercise CHD findings indicative of coronary heart disease. Isolated ECG items
254
Table 3 Prevalences (%) of coded electrocardiographic items indicative of coronary heart disease, rate ratio (RR) and rate difference (RD) among Japanese exposed and unexposed men (N Group
=
number of subjects)
"Coronary" ECG codes 1.1-3
4 1-3
5 1-3
1
4
Resting EC Gs Exposed
3
N = 417
Unexposed N = 391
"Coronary" ECG codes 11.1-3
12 1-3
15 1
29
10
22
12
Exercise EC Gs Exposed N = 404
Unexposed N = 380
Any of the "coronary" ECG codes RR Exposed
RD (%)
40
N = 417
1.1 Unexposed N = 391
4
36
RESULTS The replies to Rose's questionnaire are shown for the Japanese and Finnish exposed and unexposed workers in Table 2 The typical grade of angina was present in only two exposed Japanese men (none of the unexposed) The total prevalences for angina were 1.7 and 0 3 %, respectively The prevalences of typical angina were 4% for both the Finnish C 52 workers and Finnish unexposed workers The respective total prevalence of angina were 15 % and 10%. The prevalence of the resting and postexercise ECG abnormalities among the exposed Japanese and Finnish workers and their controls are given in Tables 3 and 4 None of the isolated "coronary" findings showed important excess in the exposed populations when they were compared with the unexposed ones The prevalences of the subjects with any "coronary" ECG finding were
255
Table 4 Prevalences (%) of coded electrocardiographic items indicative of coronary heart disease, rate ratio (RR) and rate difference (RD) among Finnish exposed and unexposed men (N = number of subjects) Group
"Coronary" ECG codes 1.1-3
4 1-3
5 1-3
4
3
9
3
6
7
Resting ECGs Exposed N = 237 Unexposed N = 233
"Coronary" ECG codes 11.1-3
12 1-3
15 1
Exercise ECGs Exposed N = 228
7
15
5
Unexposed N = 226
6
12
2
Any of the "coronary" ECG codes RR Exposed N = 236
3
Unexposed N = 233
24
1.2
RD (%)
6
40% and 36 % for the Japanese exposed and unexposed men, respectively, and 30 % and 24 % for the Finnish exposed and unexposed workers, respectively None of the workers in the two Japanese groups had evidence of past myocardial infarction (Minnesota code 1 1-2 and 5 1 or 2 1 and 5 2); this absence of "infarction" items corresponded with the scanty yield of subjective symptoms. The simultaneous occurrences of angina and "coronary" ECG items among the Finns are discernible from Table 5. The Japanese series displayed no important differences with regard to blood pressure The systolic and diastolic blood pressures were significantly higher among the Finnish exposed men as compared to the unexposed ones, as shown by Table 6 The systolic and diastolic blood pressures in both sets of groups are illustrated by Table 6 Cigarette smoking was unrelated to the
256
Table 5 Occurrence of angina pectoris and "coronary" ECG items in Finnish exposed and unexposed groups Angina
Exposed
Unexposed
"Coronary" ECG
"Coronary" ECG
+
Total
+
Total
Typical Probable Possible Atypical None
9 8 7 26 116
6 3 3 9 49
15 11 10 35 165
6 3 8 26 133
3 1 1 5 47
9 4 9 31 180
Total
166
70
236
176
57
233
Table 6 Systolic and diastolic blood pressures (mm Hg) among the Japanese and Finnish exposed and unexposed men (M = mean; SD = standard deviation; N = number of subjects) Blood pressure (mm Hg)
Systolic
M SD
Diastolic
M
Japanese
Finnish
P
Exposed
Unexposed
Exposed
Unexposed
122 13
124 14
140 19
135 18
75
77
88
9
10
13
83 12
<0.01 SD
occurrence of "coronary" ECG items in both sets of series No correlation emerged between the exposure history and prevalence of "coronary" EC Gs either in the Japanese or in the Finnish exposed groups.
DISCUSSION The results did not reveal any definitely excessive prevalence of "coronary" ECG findings within the exposed groups as compared to the unexposed groups Neither did the prevalences for angina pectoris nor the blood pressure values differ markedly between the Japanese exposed and unexposed groups By contrast, the Finnish exposed subjects experienced anginal pains more frequently, if all grades were considered, and they had higher blood pressures than their controls. Superficially, these results might suggest that CHD is not more common among the Japanese workers exposed to C 52 than among
257
unexposed men However, the amount of CHD in a population is not easily estimated from a prevalence study because of the sudden, and often fatal, outcome of its more severe manifestations, and an underassessment of the frequency of the disease occurs in such a study design The characteristics of those individuals who had died from CHD were not available in this study, and they may have differed from those found in workers who survived or who, for example, had only angina Similarly the features of those who had been removed from C52 exposure may differ from those who had had stamina against the disease For these reasons it is more appropriate to consider those features and correlates of CHD which we actually examined, i e , blood pressure, angina and ECG abnormalities, rather than the disease as a whole. The information provided by the methods used in our study must be evaluated by their sensitivity (i e , yield of few falsenegative results) and specificity (i e , yield of few falsepositive results) The determination of sensitivity and specificity of the results would, however, require a reliable means of identifying CHD in vivo, and such a means has not yet been developed Thus, our study must be evaluated with the present knowledge of the methods employed. The history of myocardial infarction or typical angina, or both, is reported to have a high (90%) predictive power in the presence of noteworthy coronary artery lesions in angiograms in clinical cases of CHD (Borer et al , 1975) On the other hand death may occur without previous warning and silent myocardial infarction may occur without symptoms (Lindberg et al , 1960 ; Lovel and Prineas, 1971 ; Romo, 1973) Both are unpredictable complications of the underlying disease, and either may be its first and only manifestation But false-positive replies in terms of reported chest pain from causes other than CHD are also notoriously common (Rose, 1968 ; Zeiner-Henriksen, 1972). The sensitivity of the symptom of chest pain in detecting CHD has not yet been determined because the prevalence of falsenegative responses is not definitely known for any population. A low sensitivity (many false-negatives) of Rose's questionnaire in our study might invalidate the results But if the questionnaire examination is considered sufficiently sensitive for epidemiologic studies on CHD, as recommended, e g , by WHO, our results would argue in favor of a high sensitivity among the Japanese workers In other words, there would be only a few, if any, false-negative cases among them. Other prevalence studies of angina pectoris employing the same questionnaire afford some comparison with the present study Pybrala et al (1974), in a recent study, obtained prevalences of about 1% for typical angina, 1 to 3% for probable, and 3 to 15 % for possible angina in Finnish men aged 35 to 54 years The total prevalence of angina in that age group varied between 2 and 7% Our results indicated higher prevalences among both the unexposed and ex-
258
posed men than those observed by Pyoral& and coworkers This finding might raise a suspicion of excessive false-positive replies in our Finnish subjects In comparative studies like the present one, they do not, however, affect the rate ratio or rate difference since supposedly the prevalences of false-positives would be equally distributed between both the exposed and the unexposed groups Thus the possible low specificity of the questionnaire in the populations concerned does not introduce any bias into the relationship between C52 exposure and angina. The low yield of replies suggestive of angina among the Japanese exposed and unexposed subjects as compared, for example, with the respective prevalences among Finnish workers may result from the well-known difference in the occurrence of CHD between these two populations (Keys et al , 1967) Another possible explanation might be cultural differences that influence the attitude towards admitting the presence of pain and discomfort, and in that case the result might be a misleading basis for comparison between the two groups Anyhow, the low prevalences in the two Japanese groups do not suggest any excess morbidity from CHD in terms of angina attributable to C 52 among the Japanese workers, whereas the difference between the Finnish groups is consistent with previous evidence of excess CHD attributable to C 52 exposure (Hernberg et al , 1970, 1973 ; Tolonen et al , 1975). When the validity of the exercise ECG examination is evaluated, two general applications must be considered: diagnostic and epidemiologic The usefulness of exercise stress testing has been reviewed recently by many authors (Blomqvist, 1971 ; Redwood and Epstein, 1972 ; Hartley, 1975), and an overall assessment of the results of virtually all published studies indicates that presently employed stress tests are not sufficiently sensitive or specific to aid satisfactorily in the diagnosis of CHD in an individual patient However, ECG exercise stress testing is generally accepted as a valuable tool in epidemiologic studies of ischemic heart disease Specifically, the disturbing effect of low specificity, a nuisance in the individual diagnosis, can be eliminated in comparative studies like the present one For example, if a 0 5 mm ST-segment depression is considered diagnostic, a large number of false-positive diagnoses probably result at the individual level, but these false positives are assumably equally distributed in both the exposed and unexposed populations and interest is focused on the rate ratio and rate difference. The specificity of an exercise ECG depends to a large extent on subject selection Expectedly, an exercise ECG has a very high specificity in a population in which most of the subjects have a history strongly suggestive of CHD, but a low specificity when such subjects constitute a small proportion of the study population The relatively small prevalence of CHD in workers
259
exposed to C52 and their controls, as compared for example to clinical patients with a high suspicion of clinical CHD, may therefore greatly diminish the effectiveness of an ECG examination in such population studies Such a circumstance seems to be the case in the present analysis. Both sensitivity and specificity could have been improved in our study If maximal rather than submaximal stress testing had been employed, the sensitivity might have been increased On the other hand it is possible that specificity with regard to the yield of "coronary" ECGs, would be adversely affected by these higher stress levels For example, Froelicher et al (1973), in a study in which maximal treadmill exercise was used, found a prevalence of 56% of false-positive "ischemic" ECG changes in asymptomatic subjects On the other hand, specificity might have been increased with more stringent ECG criteria of myocardial ischemia The frequency of false-positive results is reportedly almost zero, if an ST-segment depression of 2 mm is present in a postexercise ECG (Mason et al , 1967 ; Cohn et al , 1971 ; McConahay et al , 1971) The advantage of employing this criterion, however, must be weighed against the disadvantage of appreciably increasing the frequency of false-negative responses which, unlike false-positives cannot be corrected in the analysis of the results (Cohn et al , 1971 ; McConahay et al , 1971). The specificity of 1 mm ST-segment depression is reportedly 87-97 % (Mason et al , 1967 ; Kassebaum et al , 1968 ; Roitman et al., 1970 ; Borer et al , 1975); and that of 0 05 mm ST-segment depression, about 83 %, respectively (McConahay et al , 1971). It was impracticable to determine the true prevalence of CHD in the present study, and the fact remains that the specificity of the factors which can be taken as evidence of CHD is low. The most unequivocal evidence of the disease is probably the existence of "ischemic" ECG items together with typical angina, but because of the low yield of this combination in this study no definite conclusions could be drawn Nonetheless, the study design provided good comparability within studies and thus eliminated the effect of the possibly low specificity (high falsepositive yield) of the techniques used The levels of specificity, it is believed, do not vary "within studies", whereas "between studies" the specificity of both the angina questionnaire and the exercise ECG might differ for various reasons and therefore make a direct comparison of the results between studies unwarranted Despite all precautions against systematic bias there are numerous uncontrollable inherent factors which may influence the results from the two different populations, such as the quality of the translation of the chest pain questions, determinations of blood pressure values by different observers, and recording of ECG tracings in different buildings with a different device and different personnel, etc For these
260
reasons the results afford only rough comparison between the studies, and the main interest should be directed towards the results within studies, which rendered the following conclusions: The rate ratio and the rate difference (the rate attributable to C 52 exposure) in the Japanese series do not indicate any excess morbidity of angina, myocardial infarction, high blood pressure or "coronary" ECG items among the workers exposed to C 52 as compared to unexposed workers when these outcomes are determined with the methods we used In this context we wish to emphasize that we have not investigated total morbidity, let alone mortality from CHD among Japanese C 52 workers. The present Japanese groups form two cohorts to be followed-up in a future prospective study planned in order to shed light on these questions. The Finnish workers exposed to C 52 experienced an increased risk for high blood pressure and angina, but hardly for "coronary" ECG items There has been subsequent evidence for excess mortality from CHD and for excess nonfatal myocardial infarctions among exposed Finnish men (Tolonen et al , 1975). Based on present and previous data from Finland (Hernberg et al , 1970 ; Tolonen et al , 1975), the conclusion seems inescapable that an exercise ECG provides an imperfect means for detecting potential excess C 52 -induced CHD morbidity Alternatively, it is possible, (although unprovable in this study) that exposure to C 52 does not at all affect adversely the coronary arteries of Japanese men; the present negative result does not rule out the possibility of a causal association between CHD and C 52 exposure in the Japanese viscose rayon industry This hypothesis is best tested by a future follow-up study on the morbidity and mortality from CHD among Japanese C 52 workers. Finally, the actual C 52 dose of the Japanese men may have differed from that of the Finns and the dose might not suffice to manifest the disease The true dose-response relationship between C 52 and the various manifestations of CHD is still an unsolved problem. Irrespective of the present disappointing ability of an exercise ECG to distinguish between populations exposed to C 52 and unexposed populations, the exercise tests are a potentially useful tool in the occupational health practice of the viscose rayon industry The identification of coronary-prone individuals is important, and the cardiovascular status of men working with C52 must be clarified with possible ECG abnormalities. Hence, in the preemployment and periodical health examination the history of angina and resting and exercise ECGs have clinical relevance; a negative result is of some assistance and subjective symptoms and ECG findings indicative of CHD should be regarded as a contraindication for exposure to carbon disulfide.
261
Acknowledgements
Our thanks are due to Ms Outi Marila and Miss Ritva Halonen who coded the EC Gs We are also indepted to Ms Pirjo Fahlstr6m for the statistical treatment of the data and to Dr Sven Punsar, M D , for his valuable guidance concerning the ECG data.
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