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Background: Exposure to respirable crystalline silica (RCS) causes emphysema, airflow limitation and chronic obstructive pulmonary disease (COPD). Slate miners are exposed to slate dust containing RCS but their COPD risk has not previously been studied., Aims: To study the cumulative effect of mining on lung function and risk of COPD in a cohort of Welsh slate miners and whether these were independent of smoking and pneumoconiosis., Methods: The study was based on a secondary analysis of Medical Research Council (MRC) survey data. COPD was defined as forced expiratory volume in 1 s/forced vital capacity (FEV 1 /FVC) ratio <0.7. We created multivariable models to assess the association between mining and lung function after adjusting for age and smoking status. We used linear regression models for FEV 1 and FVC and logistic regression for COPD., Results: In the original MRC study, 1255 men participated (726 slate miners, 529 unexposed non-miners). COPD was significantly more common in miners (n = 213, 33%) than non-miners (n = 120, 26%), P < 0.05. There was no statistically significant difference in risk of COPD between miners and non-miners when analysis was limited to non-smokers or those without radiographic evidence of pneumoconiosis. After adjustment for smoking, slate mining was associated with a reduction in %predicted FEV 1 [β coefficient = -3.97, 95% confidence interval (CI) -6.65, -1.29] and FVC (β coefficient = -2.32, 95% CI -4.31, -0.33) and increased risk of COPD (odds ratio: 1.38, 95% CI 1.06, 1.81)., Conclusions: Slate mining may reduce lung function and increase the incidence of COPD independently of smoking and pneumoconiosis., (© The Author 2016. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

In a study of slate workers in four areas in North Wales 725 workers and ex-workers who had been exposed to slate and to no other dust were seen, together with 530 men from the same area who had never been exposed to any dust. Evidence of pneumoconiosis was found in one-third of the slate workers, and 10% had degrees of pneumoconiosis that would attract compensation (category 2 or higher). The prevalence of respiratory symptoms was high, and there was evidence of an effect of both simple and complicated pneumoconiosis on lung function additional to that of age. There was a high prevalence (40-50%) of radiological lesions suggestive of healed tuberculosis in men aged over 55. Either pneumoconiosis or old tubercular lesions (or both together) could account for the current symptomatology and disability of the men.

In a study in 1975 of the mortality experienced over six years by two groups of men one group had been exposed to slate dust and the other had had no previous exposure to dust. In non-smokers there was no material excess mortality associated with past exposure to dust but in smokers there was a pronounced (26%) excess. In the slate workers the risk for smokers was on average 76% greater than for non-smokers, and increased with severity of pneumoconiosis; in those who had not been exposed to dust the risk was 50% greater for smokers than non-smokers. In ex-smokers among those who had been exposed to slate dust the risk of death was higher in those with the lower lung function initially. No such association was detected in the other groups.

The effect of oral prethcamide (Micoren) (a mixture of two related amides of crotonyl N' butyric acid) was compared with a placebo preparation in 13 patients with established chronic ventilatory failure. Part I of the study comprised a double-blind single cross-over trial with an initial assessment and two further assessments at the end of each period of one month. Prethcamide was taken in 200-mg. doses four times daily. No subjective or objective changes were noted, and in particular the resting Pco(2) showed no change.Part II of the study comprised a double-blind single cross-over trial of the short-term effect of prethcamide compared with placebo in 12 patients in chronic ventilatory failure. Frequent estimations of mixed venous Pco(2) were made with a rebreathing technique for four and a half hours after ingestion of prethcamide or placebo preparation.Following prethcamide a fall in Pco(2) level to a minimum value at 30 minutes of 93% of control values and persisting for about three hours was noted for the group as a whole. The fall represents a lowering by about 4 mm. Hg of the mixed venous Pco(2).It is concluded that, though in patients with chronic ventilatory failure prethcamide may reduce the Pco(2) in the short term, there is no subjective benefit or observable objective change following repeated administrations over a period of one month.