Determination of impulse oscillation (IOS) respiratory parameters in 382 healthy school-age children in Guangzhou area

Abstract

Impulse oscillation technique (IOS) provides a simple, rapid and non-invasive method for estimating multipe respiratory physiological parmeters such as respiratory impedance, resistance, and reactance. IOS has been available and being clinically practiced more and more in China. The results of the tests cannot be interpreted appropriately without reference values, which should be based on the same ethnic population. However, there are no such references available for Chinese children until now. Objective To characterize the passive respiratory mechanics and its variability with growth, and to establish the predicted equations for Chinese children. Methods A survey was conducted on 392 healthy Chinese school children (196 boys, 186 girls) aged 6 to 14 years from August 1998 to March 1999. Respiratory impedance (Zrs), respiratory resistance (Rrs) and reactance (Xrs) at 5, 10, 15, 20, 25, 30 and 35 Hz, resonant frequency (Fres), central and peripheral resistance (Rc, Rp) were measured with Jaeger Masterscreen IOS instrument. Measurements were carried out during spontaneous breathing and met the recommendations made by European Respiratory Society. Stepwise multiple regressions and non-linear regressions were carried out with SPSS 9.0 for Windows statistical software to identify the best predictors of IOS parameters using standing height, weight, age and gender as potential determinants. The difference of resistance at the frequency between 5 Hz and 20 Hz (R5-R20) was considered as frequency dependence of resistance. The correlation coefficients between measured data and predicted values derived from our regressions were compared with that from Lechtenboerger′s regressions. Results There was negative correlation between all parameters and height as well as age except for reactance, Zrs(Boys)= -1.048+ 234.398/height, r=-0.839, P<0.001; Zrs(Girls)=-1.148+ 244.366/ height, r=-0.812, P<0.001; negative relationships were found between R5-R20 and growth in both boys and girls. R5-R20(Boys)=0.749-0.004 3×height, r=-0.686, P<0.001; R5-R20(Girls)=0.851-0.005 1×height, r=-0.627, P<0.001. Most IOS parameters were closely correlated with standing height, followed by age and weight. Comparison revealed that all correlation coefficients between measured data and predicted values from our regressions were greater than that from Lechtenboerger′s for Chinese children. The predicted values of resistance from Lechtenboerger tended to be underestimated in the shortest children or overestimated in the tallest ones. Conclusion The results showed that as a function of age and height growth, the respiratory impedance and resistance decreased, while the respiratory reactance increased, but the variability of reactance decreased. Reference values and predicted equations for IOS parameters were presented and recommeded for use in Chinese children. Key words: Airway resistance; Respiratory function tests; Child; Reference values