Modifications of PC20 and maximal degree of airway narrowing to methacholine after pollen season in pollen sensitive asthmatic patients

Summary We examined the effect of cessation of exposure to pollen on non-specific airway responsiveness in 10 grass and/or parietaria pollen sensitive asthmatics. Three methacholine inhalation challenges were performed, the first during pollen season (seasonal period), the second 2 months after the end of season (short lime after seasonal period), and the third 5 months after the end of season (long time after seasonal period). The dose response curves to methacholine were characterized by the PC20 (provocative concentration of methacholine required to produce a 20% fall in FEV|) and maximal response plateau, if possible. A maximal response plateau on the dose-response curve was considered to he present if three or more data points for FEV1 fell within a 5% response range. The challenge was stopped when FFV1 dropped more than 50% or the highest concentration of methacholine (200 mg/ml) was reached. The geometric mean (range) methacholine PC20 increased from 1.08 (0.18–37.22) in the seasonal period to 4.67 (0.71–200) mg/ml during the long time after seasonal period (P< 0.01). On the other hand, in six subjects in whom it was possible to obtain a plateau on at least one challenge, the level of the maximal response decreased from (mean ± s.e.m.) 44.1 ± 4.9 in the seasonal period to 30 ± 4.4 during the long lime after seasonal period (P < 0.05). These results suggest that in pollen sensitive asthmatic patients, the cessation of exposure to pollen is associated with a reduction of non-specific bronchial responsiveness (PC20 and maximal degree of airway narrowing to methacholine).