The interest of FEF(25-75) in evaluating bronchial hyperresponsiveness with the methacholine test

Bronchial hyperresponsiveness is the pathogenic basis of asthma, and measurement of its intensity is investigated using the methacholine provocation test, which not only and particularly evaluates the reduction in FEV1 (PD20) but also takes forced mid-expiratory flow or FEF(25-75) (PD40) into account. The present study aims to evaluate the usefulness of both parameters.

Provocation testing was carried out in 151 patients between 7 and 22 years of age diagnosed with asthma, tracheobronchitis and/or rhinitis, using a short method that allows quantification of the methacholine administered. The subjects were divided into three groups according to the amount of methacholine needed to obtain the mentioned parameters (group 1: ≤1000μg; group 2: 1001-2000μg; group 3: ≥2001μg).

Greater variability was recorded for FEF(25-75) than for FEV1. Paired comparison among the three groups for FEV1 proved significant, in the same way as for FEF(25-75) between groups 2 and 3, and 1 and 3, but not between groups 1 and 2. Calculation was made of the amount of methacholine required to obtain PD20 and PD40 from the same dose. Only the significant differences corresponded to the comparison of group 1 versus the rest, with no differences between the means of the total mean values.

The utility of PD20 is more evident, considering the variability of PD40; the latter may be useful in patients with rhinitis or tracheobronchitis when PD20 proves scantly demonstrative.