Preshift FEVi, on the resurvey adjusted for age, height, gender, and smoking, decreased similarly. The adjusted preshift FEVi for consistently positive responders at 94.4 percent contrasted with consistently negative responders whose adjusted FEVi was 98.3 percent. Subjects who responded both times with an across-shift drop of 5 percent or more lost 267 ml over 5 years versus 180 ml (t=1.72, p=0.05) for those who never experienced sharp drops. This effect persisted after adjustments for age, height, gender, and smoking by regression analysis (data not shown).
Since assessment of the effect of consistency of across-shift change in FEVi requires reproducible spirometric tests at 4 sessions (preshift and postshift in two surveys), we lost 141 subjects (36 percent) in the analysis. We therefore compared the 244 subjects for whom we had complete data with the 144 subjects for whom we had incomplete data with regard to demographics and symptom status at the time of the first survey. Canadian helth& care mall so The groups did not differ with respect to age, years worked, gender, smoking, percent predicted FEVi, or 5-year decline in FEVi. The group with incomplete data was somewhat more likely to have byssinosis (11 vs 6 percent, p=0.1) and to have accumulated fewer pack-years of smoking at the time of follow-up (11 vs 15, p=0.09).
Longitudinal respiratory studies of occupational cohorts are not common. The few such studies on cotton textile workers have not addressed the issues of symptom and acute pulmonary function variability over time and in relation to chronic loss of lung function. In the 1970s, Molyneux and Tombleson and Fox and coworkers reported the results of a 3-year follow-up of cotton textile workers in England. Their studies were short-term follow-up investigations which reported incidence rates of byssinosis and chronic bronchitis, but neither ventilatory tests nor symptoms were found to be of value in predicting the rate of FEVi deterioration between surveys.