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Revista médica de Chile

Print version ISSN 0034-9887


SANCHEZ D, Ignacio; ALVAREZ G, Cecilia; CLAVERIA R, Cristián  and  LISBOA B, Carmen. Acoustic analysis of respiratory sounds during methacholine challenge in preschool children. Rev. méd. Chile [online]. 2001, vol.129, n.11, pp.1271-1278. ISSN 0034-9887.

Background: There are changes in inspiratory breath sound intensity in patients with airway obstruction. Airway narrowing may change sound spectral characteristics. Aim: To define the characteristics of lung sounds at standardized air flow during methacholine challenge and to compare acoustic changes with transcutaneous oxygen tension (PtcO2) during induced airway narrowing. Patients and methods: Forty asthmatic children (20 male) aged 5.2±1 years and 40 normal children (18 male), aged 5.6 ± 1 years were studied. All patients were free of respiratory tract infections one month before the study. A methacholine challenge from 0.06 to 8 mg/ml was performed; the test was ended when a fall in PtcO2 of >20% from baseline was observed or if the final concentration was reached. Subjects breathed through a pneumotachograph aiming at flows of 0.4 to 0.6 l/s. Respiratory sounds were recorded using contact sensors at the suprasternal notch and at the posterior right lower lobe. From average spectra, power at low (100-200 Hz=P1) and high frequencies (400-2000 =P2) was calculated. Frequencies below which 50% (F50) and 99% (SEF90) of the spectral power between 100 and 2000 Hz was contained, were also calculated. Results: In asthmatics, the metacholine concentration at which a 20% fall in PtcO2 was observed, was lower than in normal children (p< 0.05). There was an increase in P1 (p<0.01) and a reduction in P2 (p<0.01) during inspiration, in subjects that experienced a 20% reduction in PtcO2. Also, there was an increase in F50 and SEF99 during inspiration in lung sounds, but not over the trachea. Conclusions: Lung sounds analysis can be useful for the assessment of airway reactivity in asthmatic children (Rev Méd Chile 2001; 129: 1271-8)

Keywords : Asthma; Anti-asthmatic agents; Lung diseases, obstructive; Methacholine chloride.

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