Prevalence of respiratory abnormalities in a rural and an urban community.

Population samples stratified on sex, age and smoking habits were studied in a rural and an urban community with a low level of air pollution to establish "normal" values of parameters derived from the single-breath N2 curve, the effect of smoking on these parameters, and any differences related to an urban or rural environment. Respiratory symptoms and past illnesses, smoking habits, and residential as well as occupational history were obtained by a respiratory questionnair. Pulmonary function was assessed by the single-breath N2 test and the forced vital capacity maneuver. In "healthy" nonsmokers, residual volume/total lung capacity, closing volume/vital capacity on expiration, and closing capacity/total lung capacity were significantly related to age. The slope of phase III was related to neither height nor age. There was no significant difference in prediction equations between the 2 communities for any of these parameters. Multiple regression analysis indicated that smoking had an effect on residual volume/total lung capacity, closing volume/vital capacity on expiration, closing capacity/total lung capacity, and the slope of phase III in both sexes. Abnormal values were more prevalent among male than female smokers in both communities, the highest prevalence being found in the slope of phase III in both sexes (35 to 40 per cent). The slope of phase III and closing capacity/total lung capacity were consistently related to the current number of cigarettes smoked per day.