Background: Most studies of the rate of decline in ventilatory capacity in normal subjects take into account a relatively restricted number of factors, such as age, smoking, and dust exposure. There is increasing evidence to suggest that such a limited approach is inadequate.
Objective: To carry out a prospective study of those factors influencing the rate of decline of the ventilatory capacity in a cohort of automobile workers.
Design: Prospective cohort study.
Setting: Southern Ontario, Canada.
Participants: A cohort of 181 workers employed in assembling and spray painting the chassis of new cars, a minority of whom used paints containing isocyanates.
Measurements: All participants underwent annual anthropometric measurements. Spirometry was carried out at yearly intervals, and a questionnaire relating to respiratory symptoms and smoking habits was completed annually by all participants. Daily monitoring of the isocyanate levels was carried out.
Results: There was no indication of any effect from isocyanate exposure. The annual decline in the FEV(1) was similar to that found in other studies, with 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 FEV(1) in those > 35 years old and < 35 years old differed appreciably. The decrements in the FEV(1) in subjects < 35 years old were influenced as much by excessive weight gain as by cigarette smoking. Loss of weight in those significantly overweight was frequently associated with improved lung function.
Conclusions: While age and smoking play an important role in determining the 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 epidemiologic studies of the ventilatory capacity.