FACTORS AFFECTING THE LONG-TERM VARIABILITY OF BRONCHIAL RESPONSIVENESS IN AN ADULT GENERAL-PRACTICE POPULATION

There have been few longitudinal studies of bronchial responsiveness. We wanted to assess the long-term variability and associations of bron chial responsiveness in the general population. Spirometry, bronchial provocation tests, skin-prick tests for allergy, and respiratory sympt om questionnaires were repeated every 4 months, for 2 years (August 19 87-August 1989), in 122 volunteers recruited from a cross-sectional su rvey of population. Provocation dose producing a 20% fall in forced ex piratory volume in one second (PD(20)FEV(1)) and dose-response slope ( SL), which gives values for methacholine responsiveness, were measured in all subjects. SL correlated well with PD(20)FEV(1), but repeatabil ity was impaired in those subjects with unmeasurably high PD(20)FEV(1) . The 95% range for repeatability of PD(20)FEV(1), was +/-3.12 doublin g doses and +/-4.52 doubling slopes for SL. Bronchial responsiveness i ncreased in those with self-reported colds and reduced FEV(1), in wint er 1987-1988, and in males in winter 1988-1989. Bronchial responsivene ss increased during the summer (June-August) of both years, significan tly in year 1. We conclude that bronchial responsiveness showed minor seasonal variability and that colds were the strongest predictors of i ncreased bronchial responsiveness over the 2 yr period.