DISTRIBUTION OF BRONCHIAL RESPONSIVENESS IN A GENERAL-POPULATION - EFFECT OF SEX, AGE, SMOKING, AND LEVEL OF PULMONARY-FUNCTION

Bronchial responsiveness (BR) was assessed by the methacholine challen ge test in 1,694 subjects from a sample of the general population (age d 8 to 73 yr) enrolled in a prospective epidemiologic study on the nat ural history of chronic obstructive pulmonary disease (COPD). Informat ion on respiratory symptoms and risk factors for COPD were obtained wi th a standardized questionnaire. The provocative dose causing a 10%, 1 5%, and 20% decrease in FEV(1) was reached in 939 (55%), 658 (39%), an d 447 (26%) subjects, respectively, after the last cumulative dose of methacholine (i.e., 4.8 mg). The slope of the dose-response curve was also computed in order to attribute a parameter to subjects who did no t reach the provocative dose. After natural log transformation, the sl ope (Ln Slope) of the curve showed a significant association with the degree of airway obstruction, as assessed by FEV(1)% predicted, FEV(1) /VC%, and FEV(1)/FVC%. Therefore, relationships between BR, sex, age, and smoking were evaluated after adjustments for the initial airway ca liber (FEV(1), FEV(1) adjusted for height, and FEV(1)/VC%). Females sh owed significantly higher values of Ln Slope than did males after adju stments were made for baseline lung function. In males, higher BR was observed in childhood-adolescence age groups and at older ages, while in females a higher level of BR was observed during childhood. Signifi cantly higher Ln Slope values were found for females who currently smo ked than for non- and ex-smokers. No difference was observed in males in relation to smoking habit. A dose-response trend, taking daily ciga rette smoking into account, was found in females but not in males. Our data confirm the importance of considering the initial airway caliber in assessing independent effects of age, sex, and smoking on BR. Afte r taking into account initial airway lung function, females show a hig her degree of BR than do males for all age groups, with the exception of children less than or equal to 12 yr. In addition, in females BR de clines after childhood and then remains the same, whereas in males BR declines after childhood, and then rises again in later life. Airways of females appear more susceptible to cigarette smoking than do those of males.