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
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.
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 FEV1 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 FEV1 in
those > 35 years old and < 35 years old differed appreciably. The
decrements in the FEV1 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.
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.