Respiratory impedance response to a deep inhalation in asthmatic children with spontaneous airway obstruction

The aim of the study was to determine whether the bronchomotor effect of a deep inhalation (DI) may be detected during tidal breathing in asthmatic children with spontaneous airway obstruction (AO). Two groups of children aged 5-15 yrs were studied. AO was mild in group 1 (n=12, forced expiratory volume in one second (FEV1) greater than or equal to75% predicted) and moderate-to-severe in group 2 (n=9, FEV1 less than or equal to70% pred). The forced oscillation technique at 12 Hz using a head generator allowed the determination of respiratory resistance in inspiration (R-rsi) and expiration (R-rse) before and after DI, at baseline and after salbutamol. At baseline, Rrsi but not Rrse was found to decrease significantly after DI in group I but not in group 2. The change induced by DI was significantly different in group 1 (-1.5+/-0.5 hPa.s.L-1) compared to group 2 (6.5+/-0.5 hPa.s.L-1) and exhibited significant negative correlation to FEV1 % pred. After salbutamol, DI had no effect. In conclusion, asthmatic children show a bronchomotor response to deep inhalation that depends on the degree of airway obstruction. The effect is more readily demonstrated in inspiration than in expiration.