Objectives: To determine 1) the level of specific bronchial reactivity by challenge with flour and 2) the criteria of positivity using a new method for the expression of the results.
Method: Thirty-eight asthmatic subjects, occupationally exposed to wheat flour, performed a challenge with lactose then with flour. The instantaneous measurement of the concentration and of the inspiratory airflow were used to calculate the inhaled dose and to establish the dose-response relationships. The results were given 1) by the dose of flour provoking a 20% fall in FEV1 (PDf20), 2) by the comparison of the variation of the FEV1 during the challenge with flour to the distribution of the values observed during the challenge with lactose (inferior limit of the confidence interval at 99.7%).
Results: The variations of the FEV1 were not significantly related to the inhaled dose of lactose. The specific bronchial reactivity to flour was a continuous data and three groups were distinguished: 1) subjects (n = 15) with high bronchial reactivity had a fall of FEV1 of more than 20% 2) subjects (n = 13) without significant variation of the FEV1 for doses higher than 1,400 micrograms by comparison to the distribution of the values of the lactose test 3) subjects (n = 10) with a significant fall of FEV1 by comparison to the distribution of the values of the lactose test but lower than 20%. For this group with moderate reactivity, the flow of the inhaled dose may be determinant for the bronchial response.
Conclusions: PDf 20 measures the specific bronchial reactivity. However, if the fall in FEV1 is lower than 20%, the specific challenge with flour may be compared to the challenge with lactose to detect the subjects with moderate reactivity. Our results confirmed the role of the inhaled dose and suggested the role of the dose rate in the outset of bronchial obstruction among asthmatic subjects.