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With the use of the forced oscillation technique, respiratory input impedance was measured in 371 healthy children, aged 5-12 years. How impedance values varied with height (age) and gender and to what extent negative frequency dependence of oscillatory resistance existed in these children was investigated. Negative frequency dependence of resistance between 8 and 28 Hz was a common finding in all height categories. With increasing height, resistance decreased and reactance increased in all children. Below 140 cm of height, resistance values at 8 Hz were higher, and reactance values at 8 Hz were more negative in girls than in boys. At heights above 140 cm the reverse was found. Resonant frequency was found to be higher in boys than in girls. The incidence of negative frequency dependence of resistance (FD) decreases during growth. Over heights of 130-160 cm, more negative FD existed in boys than in girls. It can be concluded that negative FD between 8 and 28 Hz can be found in healthy children up to 12 years of age, most pronounced in boys, not necessarily implicating pulmonary pathology.

The aim of this study was to determine whether impedance values in children with various chronic respiratory complaints differed from those observed in symptom-free children.Respiratory impedance was measured using the forced oscillation technique in 1,776 Dutch children aged 6-12 yrs. In addition to the commonly used parameters of resistance and reactance, further impedance parameters were obtained by using linear and quadratic regression to describe individual resistance and reactance curves as a function of frequency. Furthermore, the diagnostic value of the individual impedance parameters was evaluated by means of receiver operator characteristic (ROC) curves. Statistically significant differences in impedance values were found in girls with symptoms suggesting asthma compared to symptom-free girls, but not in boys. In children with chronic cough, impedance was not significantly different from the values of symptom-free children. The results obtained by the additional impedance parameters were comparable to those of the commonly used measures.We conclude that the diagnostic value of the impedance parameters appeared to be low, as no cut-off points were found to discriminate clearly between symptomatic and symptom-free children. These findings may reflect absence of functional abnormalities in symptomatic children at this age. Eur Respir J., 1997; 10: 88-93 Using the technique of forced oscillations (FOT), the mechanical properties and the frequency-dependent behaviour of the respiratory system can be determined. The FOT yields values for the total resistance (Rrs) and reactance (Xrs) of the respiratory system. The measurements are noninvasive, independent of effort, and require little or no co-operation from the subject. Therefore, they can be performed easily, especially in young children. Respiratory impedance has been studied in adults [1][2][3][4], as well as in children [5][6][7][8][9][10][11][12][13], in various clinical and epidemiological settings. Recent reports have suggested that the technique may be a suitable tool for epidemiological studies [14,15].Recently, we have reported resistance and reactance values at 8 and 28 Hz, in 371 normal children aged 6-12 yrs [16]. All impedance parameters were significantly related to height and varied between sexes. Negative frequency dependence of resistance between 8-28 Hz was a common finding, most pronounced in (young) boys. Furthermore, we have reported differences in impedance values between children with (n=110) and without (n=360) asthma-like symptoms [17]. The analysis of these was restricted to mean values at single frequencies in the frequency range 8-28 Hz. At present, more information on the impedance versus frequency curves (4-48 Hz) can be obtained, due to further computerization of the impedance data.The aims of the present study were to analyse the relationship between various respiratory symptoms, such as chronic cough or asthma, and the frequency dependence of the respiratory impedance compared with those of symptom-free children i...

The aim of the present study was to determine the prevalence of asthma-related symptoms in a group of primary school children, by means of a questionnaire completed by their parents, and their lung function using spirometry and the forced oscillation technique (FOT). Also investigated were diagnostic labeling and medical prescription. We approached 535 children, from two primary schools in Maastricht, the Netherlands. Completed questionnaires were received from 482 children (90%). Valid lung function values were obtained in 470 of these children (98%). The lifetime prevalence of wheeze and attacks of shortness of breath with wheeze was 29% and 19%, respectively. The period prevalence of wheeze was 15%, 13% reported chronic cough, and 10% attacks of shortness of breath with wheeze. The doctor-diagnosed asthma and bronchitis prevalence was 6% and 19%, respectively. Of the children diagnosed as having asthma, 69% used antiasthma medication; none of the children diagnosed as having bronchitis used antiasthma medication. A symptom-based asthma prevalence of 11% was calculated. Statistically significant differences in spirometric and FOT indices were found between the children with and without complaints. In conclusion, among the 482 investigated children a relatively high prevalence of unrecognized or misclassified, and therefore undertreated, asthma-related symptoms was found. These observations were confirmed by the lung function data, in that we found significant differences in spirometric and FOT indices between children with and without complaints.

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