Influence of relative humidity and repeated exercise on exercise-induced bronchoconstriction

The relationship between previous exercise-induced bronchoconstriction (EIB) of different magnitude and the pulmonary response to exercise 1 h later was examined in asthmatic children. After acclimatization they performed repeated, paired exercise tests in a clean-air climatic chamber at 23 degree C. The first test of each pair was carried out in 15%, 50% and 85% relative humidity (RH), respectively, to produce different degrees of EIB. All second tests were performed in 50% RH. Changes in pulmonary function were assessed by measuring PEF and FEV1. Bronchodilatation during exercise was not influenced by RH, whereas dry air increased and humid air decreased the bronchoconstrictive response to exercise. When both tests were performed in 50% RH, the second test caused significantly less EIB than did the first test. However, no differences were found between the three second test responses. This suggests that the relative refractoriness after an episode of EIB is not related to the severity of previous bronchoconstriction, but could be associated with exercise as such or other mechanisms in EIB.