Reproducibility of responsiveness to a standardized bronchial allergen provocation—Rt compared to FEV1 as measurement of response to provocation

Standardized bronchial allergen provocation was performed twice in nineteen extrinsic, well defined, stable asthmatic patients, with an interval of median 15 days (range 14–19) to study the reproducibility of the bronchial response. Smoking and medications were withheld prior to the provocation after a rigid scheme. Ten-fold increasing concentrations of allergen solution 0.9 ml were inhaled by tidal volume breathing for 5 min with intervals of 10 min. The bronchial response to inhaled allergen was determined by forced expiratory volume in the first sec (FEV₁) and by total resistance to breathing (R_t) determined by an opening interrupter method. The provocation was continued until an allergen concentration causing at least 20% decrease of the postsaline FEV₁ or a 40% increase in R_t was reached. A PC₂₀-FEV₁ and a PC₄₀-R_t was calculated by interpolation on the log-dose-response curve. The reproducibility of PC₂₀-FEV₁ allergen was high with a 95% confidence interval (CI) for a single determination being the observed value ±0.83, ten-fold concentration difference, the intraclass correlation (IC) was 0.99 and the coefficient of variation 8.46%. Concerning PC₄₀-R_t a 95% CI for a single determination was calculated being the observed value ±0.58, ten-fold concentration difference, IC was 0.99 and the coefficient of variation was 5.79%. No significant correlation was found between differences in pre-challenge FEV₁ and R_t values and the corresponding PC₂₀-FEV₁ and PC₄₀-R_t values. Least square regression between PC₂₀-FEV₁ and PC₄₀-R₁ was performed for the first and the second provocation (P < 0.05). We conclude that bronchial allergen challenge performed in stable asthmatics is highly reproducible and as such a valuable test in the diagnosis of allergic asthma when connected with anamnesis, skin-prick test and the level of specific immunoglobulin E in peripheral blood.