During induced bronchial constriction there is a reversible decrease of inspiratory and an increase of expiratory sound intensity [Pasterkamp et al. Ped Pulmonol. 1997;23:21]. To test if the critical flow (Vcrit), i.e., the flow required to generate breath sound that is significantly different from sound during breath hold, changes accordingly during bronchial narrowing, we studied children during methacholine (MCh) bronchial challenge. We recorded sound over the posterior right lung of 26 children with suspected asthma, 14 male, age 6-17 y. Air flow (pneumotach) and lung sounds (contact sensor) during tidal breathing and at target flow of 15 ml/s/kg were recorded for 40 s at baseline (BAS), after the final MCh concentration (FIN) and again 10 min after inhalation of 200 μg salbutamol (ABD). Lung sound during 5 s of breath hold at the end of each recording was included. Spirometry followed each recording. Average Fourier spectra of lung sound excluding wheeze were computed and the sound intensity within a frequency range from 150-300 Hz was measured. Vcrit increased significantly during inspiration only in the group that had a positive response (ΔFEV1 -32±7.7%; mean±S.D.). Vcrit decreased significantly during expiration also in the group with a negative response (ΔFEV1 -8.3±5.4%). The changes in Vcrit were reversible after salbutamol (see Table). We conclude that Vcrit during expiration is very sensitive to changes in airway caliber(82%) but is not a specific indicator of bronchial hyperresponsiveness (50%). Vcrit during inspiration, however, may add a useful parameter to the acoustical detection of positive bronchial challenge tests in children.

Table 1 No caption available.
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