Longitudinal study of lung function development in a cohort of Indian medical students: interaction of respiratory allergy and smoking

This study was done to identify some factors that affect the growth and development of lung function during adolescence and early adulthood. Forced expiratory spirograms and peak expiratory flow rates were obtained in a cohort of normal young men (n = 63) over a period of 4 years, at intervals of approximately 2 years. Two factors that disturbed the normal pattern of lung function development in this group were smoking and respiratory allergy. Among the smokers and the allergics the decline in the forced expiratory volume expressed as a percentage of the forced vital capacity (FEV1%), the forced expiratory flow in the middle half of the forced vital capacity (FEF25-75%) and the FEF25-75% expressed as a ratio of the forced vital capacity (FEF/FVC) was more than double that among the normal subjects. The number of smokers and of allergics increased during the course of the study from 15 to 19 and from 16 to 23 respectively. There was a significant (P less than .01) interaction between smoking and the manifestation of respiratory allergy. Among nonsmokers, the number of allergic subjects increased from 12 to 13, while among smokers it increased from 4 to 10, during the four years.