Modulation of airway caliber by deep inhalation in children

To elucidate whether deep inhalation (DI) modulates changes in airway caliber in childhood, we measured the effect of DI on respiratory impedance before and after inhaled methacholine or salbutamol in 4- to 7-yr-old children (n = 15) suffering from recurrent wheezing. In all children, the real part of impedance between 12 and 16 Hz (Re[Z]_12-16) increased after methacholine from 5.6 ± 1.2 to 8.2 ± 1.6 cmH₂O·l^-1·s (P <0.001) and resonance frequency from 18 ± 3 to 25 ± 5 Hz (P <0.001). These changes were partially reversed by DI: Re[Z]_12-16 decreased to 7.2 ± 1.2 cmH₂O·l^-1·s (P <0.01) and resonance frequency to 19 ± 5 Hz (P <0.001). In nine children, on a separate occasion, Re[Z]_12-16 decreased after salbutamol from 8.3 ± 1.9 to 5.1 ± 0.9 cmH₂O·l^-1·s (P <0.001) and resonance frequency from 21 ± 6 to 15 ± 3 Hz (P <0.05). The decrease of Re[Z]_12-16 was partially reversed by DI (to 6.2 ± 1.4 cmH₂O·l^{- 1}·s, P <0.01), but resonance frequency did not change significantly (P = 0.75). We conclude that in 4- to 7-yr-old children pharmacologically induced changes in airway caliber are modulated by DI. These findings suggest that airway-to-parenchyma interdependence is operative in this age range.