The relationship between ventilatory capacity and simple pneumoconiosis in coalworkers; the effect of population selection.

Abstract

The diagnosis in life of coalworkers' pneumoco niosis is based on the industrial history and the chest radiograph. The most striking complaint is excessive breathlessness on exertion. The relationship of this symptom to radiological abnormality is of practical importance in assessing compensation; in most schemes the assumption is made that if a readily diagnosable degree of pneumoconiosis is present and the man is breathless, then the breathlessness is caused by the pneumoconiosis if no other cause is apparent. This assumes a reasonably close rela tionship between radiological abnormality and breathlessness after allowing for the effects of age. In full reviews of the literature, Worth and Schiller (1954), and Gilson, Hugh-Jones, Oldham, and Meade (1955), conclude that complicated pneumoconiosis is a cause of moderate or severe breathlessness and the extent of the radiological abnormality relates reasonably well to the degree of breathlessness when age is taken into account. The position in the case of simple pneumoco niosis is far less certain. A number of investigators (J?quier-Doge and Lob, 1945; Martin and Roche, 1946; Lob, 1947; McVittie, 1949; Theodos, Gordon, Lang, and Motley, 1950; Wright, 1942 and 1946; Gilson, and others, 1955) have found this relation ship is not particularly close. At least part of the variability between the findings of different investi gators may be ascribed to the effect of bias introduced in the method of selection of the subjects studied. It has, therefore, been our aim to assess the likely magnitude of this effect and obtain a more certain relationship by studying representative groups of miners and ex-miners. The reproducibility of the radiological diagnosis of coalworkers' pneumoconiosis and the measure ment of observer variability have been discussed in previous papers from this Unit (Fletcher and Oldham, 1949 and 1951). Other aspects of the significance of simple pneumoconiosis in coalworkers' pneumoconiosis have been considered elsewhere: its relation to the development of complicated pneumoconiosis (Fletcher, 1948; Mann, 1951; Cochrane, Davies, and Fletcher, 1951); its relation to life expectancy (Carpenter and Cochrane, 1956); to dust exposure (Roach, 1953), and to dust content in the lungs (King, Maguire, and Nagelschmidt, 1956). The most direct assessment of breathlessness is by questionnaire, but there are difficulties in its use, particularly in men applying for compensation. Objective measurements, if they are sufficiently highly correlated with the man's principal symptom, have great advantages for studying large and varied groups of subjects. In an evaluation of tests of the main aspects of lung function in miners with pneumoconiosis, Gilson and others (1955) found that ventilatory capacity measured by maximum voluntary ventilation was better related to an independent assessment of breathlessness (r = 0-77) than any other single test, and only slightly less well correlated than the index obtained by expressing the ventilation on exercise as a percentage of the maximum voluntary ventilation?a test which has been shown by many workers to be reasonably well related to dyspnoea (Cournand and Richards, 1941 ; Wright, 1942; Warring, 1949). The physiological tests were more sensitive than the clinical assessments. The maximum voluntary ventilation is a simple test, but it takes longer and causes rather more discomfort to the subject than measuring the ventilatory capacity by a single forced expiration. A number of studies of the relationship between the maximum voluntary ventilation and the volume expelled during the first part of a forced expiration (Roche and Thivollet, 1949; Tiffeneau, Bousser, and Drutel, 1949; Kennedy, 1953; McKerrow, 1955; Bernstein and Kazantzis, 1954; Leuallen and Fowler, 1955) have in general shown a high correlation between the two. Direct comparison of both tests, and a study of the relation of the results of the single breath method with the clinical grading of dyspnoea 166