Characterization of asymptomatic subjects with exercise-induced bronchoconstriction (EIB)

Spirometry verified EIB can be detected in population-based studies in subjects without exercise-induced airway symptoms. The value of this finding is not clear. We investigated if these individuals differ with regard to response in airway resistance measured by forced oscillation technique (FOT) and baseline fractional exhaled nitric oxide (FeNO) in subjects with EIB and with or w/o exercise-induced symptoms. A total of 146 subjects (13-15 years) from a population-based study, performed a visit with measurement of FeNO, FEV1 and respiratory resistance at 5 Hz (R5), before and after exercise challenge. EIB (fall in FEV1 ≥10%) was found in 48 subjects. A larger increase in post-exercise R5 and higher FeNO levels were found in the groups with EIB with airway symptoms compared to the EIB group w/o symptoms (Table). The EIB group w/o symptoms did not differ in R5 (21.9 vs 22.4, p=0.84) or FeNO (10.7 vs 11.6 ppb, p=0.72) compared to a control group w/o both EIB and symptoms. No differences between EIB groups were found in the degree of fall in FEV1 (all comparisons p>0.05). In conclusion, subjects with EIB, but without respiratory symptoms do not present signs of airway inflammation or increase of respiratory resistance in relation to exercise. In contrast, increase in resistance and airway inflammation was found in symptomatic subjects with EIB.