Respiratory impedance response to a deep inhalation in children with history of cough or asthma.

Abstract

The aim of this study was to describe the change in respiratory impedance induced by a deep inhalation (DI) in children who developed a positive response to inhalation of methacholine (Mch). Eighteen children aged 4.5-12.5 years, presenting with chronic cough or doctor-diagnosed asthma, were studied at baseline after inhalation of Mch and after inhalation of a bronchodilator. Respiratory resistance (Rrs) and reactance (Xrs) were measured by the forced oscillation technique, varying transrespiratory pressure at 12 Hz around the head. The tidal flow (V') and volume (V) dependence of Rrs before and after the DI was characterized according to the equation Rrs = K1 + K2 x /V'/ + K3 x V. DI induced no significant change at baseline or after inhalation of a bonchodilator. During Mch challenge, Rrs and K1 were significantly lower, and K3 and Xrs significantly less negative after DI than before, during both inspiration and expiration; there was no change in K2. We conclude that DI results in a decrease in Rrs in children with induced bronchoconstriction. The associated changes in Xrs, K1, and K3, and lack of decrease in K2, suggest that dilatation of airways occurs at the bronchial level, with little contribution of the upper airways or of a change in breathing patterns.