EXERCISE-INDUCED ASTHMA: RESEARCHING PREDICTORS IN SUBJECTS WITH MILD ASTHMA

PURPOSE: Aim of the study was to identify the functional respiratory parameters able to predict the development of EIA in patients suffering of mild asthma. METHODS: In 20 patients with mild asthma and suspected of previous EIA, after adequate drugs wash-out, baseline pulmonary function tests and non-specific bronchial stimulation with methacholine were performed. The next day they underwent a symptoms-limited incremental cardio-pulmonary exercise test (CPExT) with measurements of FEV1 at 1,3,5,7,10,15 minutes after the end of the exercise to establish the EIA development. RESULTS: Only 19 patients (aged 275 yrs) completed the two-day protocol. Twelve of them experienced EIA. None of the baseline functional respiratory parameters measured at rest was able to predict EIA. In contrast with asthmatics without EIA, in those showing EIA the average Inspiratory Capacity (IC) did not increase during CPExT, because 6 of them (50%) displayed exertional dynamic pulmonary hyperinflation (DH), as documented by a progressive increase of end-expiratory lung volume. These asthmatics, who showed an earlier and larger drop in FEV1 at the end of the exercise, had lower FEF25-75% (%pred.) at rest (p<0.05) and lesser PD20FEV1 (p<0.05), as compared with those with EIA without DH. CONCLUSIONS: Although this study could not identify predictors for EIA in patients with mild asthma, it demonstrated that asthmatics with EIA who developed DH during exercise, had lower resting FEF25-75% (% pred.) and greater airway hyperresponsiveness, suggesting a prevalent small airways impairment. CLINICAL IMPLICATIONS: Physical effort is a natural stimulus capable of inducing acute airway obstruction in asthma: the so called exercise-induced asthma (EIA).