OBJECTIVEImpulse oscillation system (IOS) as an approach to lung function determination is suitable for children, especially for preschool children in that it only requires the individual to be examined to breathing stably with tidal volume. However, until now there have been no uniformly agreed criteria for positive bronchial reversibility test in clinical practice. A screening method was applied to seek for answer when this question in the hope of providing objective evidence for clinical diagnosis of respiratory diseases, esp. asthma.

METHODSOne hundred and fifty-six children patients during asthma attack were recruited randomly for this study from January to December, 2004. These patients included 103 boys and 53 girls aged from 5 to 18 years with mean age of 8.84 +/- 2.58 years, who visited the doctors in the Clinical and Educational Centre for Asthma, Capital Institute of Pediatrics and were diagnosed as asthma. Maximal expiratory flow volume and IOS lung function were determined followed by bronchodilator reversibility test in all patients. The sensitivity and specificity of IOS parameters, total respiratory impedance (Zrs), respiratory resistance at 5 Hz (R5) and reactance at 5 Hz (X5) for diagnosing asthma at different improvement levels after inhalation of bronchodilator were calculated respectively using forced expiratory volume in first second (FEV(1)) and maximal mid-expiratory flow (MMEF) as gold standard. And the regression equation between parameters of lung function which were determined with the two different methods was analyzed.

RESULTSAfter inhalation of bronchodilator, the lung function of the children was improved significantly (P < 0.01), with the FEV(1), MMEF increase and Zrs, R5, and X5 decrease. There were significantly positive correlations (P < 0.01) between the improvement rate of parameters of lung functions determined with the two methods, and the highest correlation coefficients existed between X5 and FEV(1) and MMEF (respectively 0.676, 0.571), correlation coefficients between X5 and Zrs ranked second (0.519 and 0.505, respectively). When an increase of FEV(1) equal to or greater than 15%, or increase of MMEF equal to or greater than 30% was used as reference for positive bronchial reversibility, the sensitivity and specificity were relatively high for considering positive bronchial reversibility test with at least 20% decrease of Zrs, R5, and 30% decrease of X5 with IOS lung function. The sensitivity and specificity of Zrs, R5 and X5 calculated from FEV(1) were 0.62, 0.51; 0.49, 0.54; 0.70, and 0.54, respectively. The sensitivity and specificity of Zrs, R5 and X5 calculated from MMEF were 0.63, 0.54; 0.53, 0.60; 0.60, and 0.58, respectively. The regression equation showed that the decrease of Zrs, R5 and X5 corresponding to 15% increase of FEV(1) and 30% increase of MMEF were 21.7%, 21.3%; 19.9%, 19.5%; 30.1%, and 29.6%, respectively.

CONCLUSIONWhen lung function is determined with IOS in children, only when decrease of Zrs and R5 is equal to or more than 20% and decrease of X5 is 30% or more after inhalation of bronchodilator, can the bronchial reversibility test be considered as positive.