Rise and fall of the FEV1

Background: Most studies of the rate of decline in ventilatory capacity in normal subjects take into account a relatively resulted number of factors, such as age, smoking, and dust exposure. There is increasing evidence to su ggest that such a limited approach is inadequate. Objective: To carry out a prospective study of those factors influencing th e rate of decline of the ventilatory capacity in a cohort of automobile wor kers. Design: Prospective cohort study. Setting: Southern Ontario, Canada. Participants: A cohort of 181 workers employed in assembling and spray pain ting the chassis of new cars, a minority of whom used paints containing iso cyanates, Measurements: All participants underwent annual anthropometric measurements . Spirometry was carried out at yearly intervals, and a questionnaire relat ing to respiratory symptoms and smoking habits was completed annually by al l participants. Daily monitoring of the isocyanate levels was carried out. Results: There was no indication of any effect from isocyanate exposure. Th e annual decline in the FEV1 was similar to that found in other studies, wi th the respective annual decrements for smokers, ex-smokers, and nonsmokers being 0.055 L, 0.046 L, and 0.035 L, respectively. The decline of the FEV1 in those > 35 years old and < 35 years old differed appreciably. The decre ments in the FEV1 in subjects < 35 years old were influenced as much by exc essive weight gain as by cigarette smoking. Loss of weight in those signifi cantly overweight was frequently associated with improved lung function. Conclusions: While age and smoking play an important role in determining th e rate of decline in the ventilatory capacity, it is clear that body weight plays a significant role and needs to be taken into account in all epidemi ologic studies of the ventilatory capacity.