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

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Abstract
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).