Respiratory conductance response to a deep inhalation in children with exercise-induced bronchoconstriction

Abstract

Airway response to deep inhalation (DI) may provide information relevant to the mechanisms of airway obstruction (AO). The hypothesis examined here is that DI provokes bronchodilation in children during exercise-induced bronchoconstriction (EIB). EIB was attested in 15 children aged 10±3 year (mean±SD) by a decrease in forced expiratory volume in 1 s (FEV 1)⩾15% from baseline after a free running test. The respiratory resistance was measured by the forced oscillation technique at 12 Hz using a head generator to vary transrespiratory pressure around the head. The airway response to DI was estimated by the effect on respiratory conductance (Grs), calculated as the reciprocal of respiratory resistance in inspiration. During EIB, DI induced a variable but significant increase in Grs, from 0.085±0.023 to 0.101±0.029 l hPa −1 s −1 ( P=0.0003). The post- to pre-DI Grs ratio (1.19±0.14) was found to correlate negatively with EIB-induced reduction in FEV 1 ( P=0.02), forced vital capacity (FVC) ( P=0.01) but not FEV 1/FVC, i.e., DI induced more bronchodilation in those children with small EIB associated reduction in FVC. It is concluded that the bronchodilator effect of DI may be demonstrated in children with EIB. It is suggested that the associated small airway closure and lung hyperinflation may contribute to limit this response to DI.