Profusion Of Small Opacities Research Articles

Exercise Testing in Radiologically-limited, Simple Pulmonary Silicosis

Forty-five consecutive patients (17 non-smokers and 28 smokers) affected by pulmonary silicosis with limited profusion of radiologic small opacities of "p" type underwent physical examination; resting standard pulmonary function tests (PFT); and progressive, multistage, treadmill-based exercise testing (ET). Results show that, in 78 percent of all patients, maximum oxygen uptake (VO2max) was below 80 percent of predicted, and in most cases this was accompanied by a reduction of anaerobic threshold and/or oxygen pulse. In our group, VO2max predicted was uncorrelated with PFT parameters, symptoms and x-ray picture. No significant differences in response to exercise were observed between smokers and non-smokers. Therefore, exercise was limited by factors other than ventilatory limitation. It is concluded that ET is not more sensitive than PFT for assessing ventilatory impairment in patients with early, simple silicosis, even though it may be valuable for providing information about other sources of exercise limitation.

Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia.

An estimate has been made of the prevalence of unrecognised pneumoconiosis in former crocidolite workers from Wittenoom, Western Australia. All plain chest radiographs relating to a one in six random sample (1025 men) of all former Wittenoom workers who had never entered a compensation claim to the Pneumoconiosis Medical Board of Western Australia were sought from Perth teaching hospitals and from the Perth Chest Clinic where compulsory examination of all workers in the mining industry takes place. Radiographs were recovered for 83% of the men and read independently by two observers. By means of logistic regression analysis a current prevalence of parenchymal abnormality (defined as a radiographic profusion of small opacities of category 1/0 or greater on the ILO classification) of nearly 20% was calculated after adjustment for age, time since first exposure, and cumulative exposure level. One hundred men randomly selected from those known to be alive in the sample were invited to attend for a new radiographic examination. Seventy four men attended and the predicted prevalence was confirmed. It is estimated from these data that there were between 450 and 900 former Wittenoom workers in Australia at the end of 1980 who had radiographic abnormality consistent with pneumoconiosis but had not claimed compensation or had asbestosis diagnosed. The data are consistent with there being no threshold dose of crocidolite exposure for the development of radiographic abnormality in this group.

An application of kappa-type analyses to interobserver variation in classifying chest radiographs for pneumoconiosis.

We investigated interobserver variation between three physician readers in the independent classification of chest radiographs from 1771 taconite workers for pneumoconiosis. We analysed variation with a general methodology for the analysis of categorical data, and quantified interobserver agreement in terms of kappa-type statistics. The results revealed considerable variation in the profusion of opacities reported by each observer. This was especially so for the earliest radiographic changes, but variation also occurred with the small number of films in the series showing category 2 pneumoconiosis or over. Variation in the classification of profusion of small opacities was greater in films of poor quality, and also increased with the length of time between taking and reading the film (film age). We could not account for the effect of film age by controlling for film quality, as subjectively assessed by the readers.

UNUSUAL PULMONARY OBSERVATIONS AND EXPOSURE TO COALMINE DUST: A CASE-CONTROL STUDY

Abstract A study of five doctors' classifications of 4330 miners' serial chest radiographs identified 45 cases of unusually rapid development of simple pneumoconiosis (the criterion being that at least three of the doctors judged that the increase in profusion of small rounded opacities during approx. 10-yr intervals between films amounted to two or more steps of change on the 12-point simple pneumoconiosis scale). Forty-one matched controls were selected from the same nine collieries using analogous criteria to determine the absence of any increase in the profusion of small rounded opacities. The cases had worked 926 more hours on average during the 10 yr than the controls, and their mean exposures to respirable mixed coalmine dust were also slightly higher, by 0.2 mgm'3. However, the only statistically significant differences between cases and controls in the environmental variables considered were for indices reflecting exposures to quartz in the mixed dust. The highest standardized mean difference referred to the percentages of quartz in the exposures which were 6% on average for the cases and 5% for the controls. The median quartz level in the 10-yr exposures of all 4330 men studies was 4.6%. Average rates of decline in lung function over the 10-yr intervals did not differ significantly. Smoking and breathlessness were both slightly more prevalent among the cases, but a standardized measure of timed Forced Expiratory Volume at the earlier radiological surveys was better for the cases. Progressive Massive Fibrosis (PMF) was seen on the later films from 10 cases and three controls. Attacks or progression of PMF were recorded for nine cases and one control. The disproportionately high number of attacks or progression of massive fibrosis among the cases is statistically significant at the 5% level. It is concluded that unusually rapid progression of simple pneumoconiosis accompanied by the occurrence of massive fibrosis is associated with relatively high percentages of quartz in exposures to mixed coalmine dust, but it is clear that exposure to quartz is not the sole factor responsible for the development of PMF.

Shape of small opacities and lung function in coalworkers.

Lung function and chest radiographs were reviewed in 357 coalworkers who had been referred from the Cardiff Pneumoconiosis Medical Panel. The chest films were read according to the 1980 ILO classification of radiographs by three experienced readers. An irregularity score, reflecting the shape of the small opacities, was derived from the readings and compared with the lung function variables. Men with higher irregularity scores had significant reductions in ventilatory capacity and gas transfer factor, with no change in total lung capacity, after age, height, profusion of small opacities, and smoking habit had been taken into account. The effects were present both in those with and in those without large opacities. The agreement between readers over the shape of opacities was almost as good as for their profusion. Men with rounded opacities had a lower gas transfer factor if they were predominantly of the "p" type. The results are consistent with those for a combination of emphysema and interstitial fibrosis, which has been found in coalworkers with irregular opacities.

Classification of chest radiographs for epidemiological purposes by people not experienced in the radiology of pneumoconiosis.

Under controlled conditions 16 people (eight non-medical) inexperienced in the radiology of occupational lung diseases repeatedly classified 300 selected chest radiographs using the 1971 ILO U/C International Classification of Radiographs of Pneumoconioses. Eight experienced medical readers had previously classified 220 of the selected radiographs for profusion of small rounded opacities. Variability among readers was greater in experimental panels than among the experienced readers. But the average consistency between pairs of novice readers in their use of the 12 categories of profusion for the same radiographs was similar (about 29%) to the average consistency among the experienced readers. Subsequent work with nine of the participants showed that eight of them were able to produce classifications of coal miners' chest radiographs that correlated well with estimates the miners' exposures to respirable coal mine dust. It is concluded that the ILO classification scheme provides a sound descriptive system for recording the appearances of chest radiographs. Under controlled conditions the scheme may be used for epidemiological studies by those with no specialist knowledge or clinical experience. This presupposes that the radiographs concerned will have been examined previously for diagnostic purposes by a suitable qualified physician.

Epidemiological study of respiratory disease in workers exposed to polyvinylchloride dust.

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 cross-sectional 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. The forced expired volume in one second (FEV1) and forced vital capacity (FVC) were inversely related to dust exposure after age, height, and smoking effects had been taken into account. This effect was seen principally in cigarette smokers, and there was suggestive evidence that PVC dust exposure and cigarette smoking interacted in the reduction of FEV1 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 0/1 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 effect of PVC dust on the appearance of the chest radiography. These appearances were so slight that only the higher sensitivity of this reader 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 FEV1 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 loss of lung function as a result of their occupation.

Assessing the radiological progression of simple pneumoconiosis.

The Medical Service of the National Coal Board has recently issued the fourth in a series of medical research memoranda, in which the results of studies carried out on various aspects of the health of men working in this large industry are made generally available (Liddell and May, 1966). This memorandum is concerned with the technical aspects of what seems at first a simple matter? detecting and measuring increases in the amount of abnormality attributed to simple pneumoconiosis in the chest radiographs of coalminers. Simple pneumoconiosis is classified under the International Labour Organization (I.L.O.) system into four categories of increasing profusion of small opacities. The uncountable number of visible small opacities forms a continuum of abnorm ality, and the progression which is to be detected, whatever its significance, is an increase in this number. Sometimes progression produces a change of category, when the increased number of opacities takes the film across a category boundary; some times an equal increase of the number of opacities leaves the category unchanged, the progression being entirely within the boundaries of the original category. Thus the number of changes of category seen, when a group of men is x-rayed on two occasions some years apart, is not necessarily a sufficient index of the amount of progression. It may depend too much on how the men's radio graphs were distributed along the continuum of abnormality on the first occasion, in particular on the proportion of films showing virtually no small opacities at all. A major improvement in an index of this kind was effected by LiddelPs (1963) dis covery that readers of radiographs could easily indicate for each film read whether the I.L.O. category above or below the one finally chosen had been considered as a serious alternative. In this way the 4-point scale of the I.L.O. classification was effectively turned into a 12-point scale, on which the number of steps taken by each man could form an index which would respond more closely to increases in the number of opacities in the man's film.