Respiratory symptoms and ventilatory function changes in relation to length of exposure to cotton dust.

The prevalence of byssinosis, respiratory symptoms, acute changes of ventilatory capacity over the shift, and chronic changes of ventilatory capacity were studied in two groups of non-smoking female workers exposed to practically identical concentrations of the same type of cotton dust but for very different periods of time (16 and 4 years respectively). The prevalence of non-specific respiratory symptoms increased with the duration of exposure to cotton dust only in the subjects with byssinosis. Exposure to cotton dust caused significant reductions over the shift of the mean FEV1.o, FVC and PEF in all the groups of cotton workers examined. In byssinotics the reduction in ventilatory capacity was considerably greater in subjects with longer than in those with shorter exposure to cotton dust, while in non-byssinotics the response was approximately equal in the two groups. Inhalation of a bronchodilator at the end of the shift restored ventilatory function to its pre-shift values except in byssinotics with a longer duration of exposure to cotton dust. Chronic changes of ventilatory capacity developed only in subjects with a longer exposure to cotton dust and were common in the byssinotics. Numerous epidemiological studies have shown that exposure to cotton dust may cause respiratory symptoms accompanied by changes of lung function. The diagnosis of byssinosis is based on the characteristic history of chest tightness, cough, and wheezing, predominantly on the first working day after a break of more than one day of exposure to active dust. Later, the same symptoms occur on subsequent days of the week, and chronic cough and dyspnoea may persist even during absence from work. Evidence of irreversible ventilatory insufficiency may then be found (1958). Their findings have been confirmed by others in different countries (Schilling, Bouhuys, and Gilson, 1971). Reports conflict on the relationships between the duration of exposure to vegetable dust and the prevalence of byssinosis and acute respiratory response. While Molyneux and Tombleson (1970) found a steady increase of byssinosis with duration of exposure up to 29 years in their study of 1,359 cotton workers, Batawi, Schilling, Valic, and Walford (1964) and Bouhuys et al. (1969) had not observed this relationship. Batawi et al. (1964), however, found a high significant correlation between the fall of indirect maximum breathing capacity during the shift and the incidence of byssinosis. The present study was undertaken to assess the influence of the duration of exposure to cotton dust on the development of symptoms …