title: [Computer analysis of respiratory sounds in bronchial obstruction evaluation in small children that do not collaborate with spirometry tests].
abstract: BACKGROUND
  There are changes in inspiratory breath sound intensity in patients with airway obstruction. Airway narrowing may change sound spectral characteristics.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Departamentos de Pediatría y Enfermedades Respiratorias, Escuela de Medicina, Pontificia Universidad Católica de Chile, Lira 44 1er piso, Santiago, Casilla 114-D, Santiago, Chile. igsan@med.puc.cl
authors.forename: I
authors.initials: I
authors.lastname: Sánchez
authors.forename: C
authors.initials: C
authors.lastname: Alvarez
authors.forename: C
authors.initials: C
authors.lastname: Clavería
authors.forename: C
authors.initials: C
authors.lastname: Lisboa
mesh_terms: D001249:Asthma / Q000175:diagnosis*; D001314:Auscultation / Q000379:methods; D001785:Blood Gas Monitoring, Transcutaneous; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D012135:Respiratory Sounds / Q000175:diagnosis*; D012815:Signal Processing, Computer-Assisted
chemical_list: D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride