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The effects of smoking habits, socio-occupational factors and respiratory symptoms in the development of airflow obstruction have been studied in a working population of 575 men aged 30-54 in 1960 and surveyed in 1960 and 1972. On average, FEV1 decreased by 47 ml/annum. Apart from FEV1 level, which reflects loss since the beginning of adult life, three factors were independently related to FEV1 slope: tobacco consumption, occupational exposure and social class. The decrease of FEV1 with smoking was dose related and decelerated among those who stopped smoking. This follow-up study ruled against phlegm as a causal factor of early stage airflow obstruction, although its role is not excluded at later stages.
Kauffmann et al. (Mon,) studied this question.