Low diagnostic value of respiratory impedance measurements in children

Abstract

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...

Identifying pediatric lung disease: A comparison of forced oscillation technique outcomes

“…The sensitivity and specificity values were calculated from these z-scores and utilised to construct the curve. The line of identity (---) shows the area of the curve where the diagnostic ability is 50% and therefore equal to chance correlation between FOT results and physiological data, in conjunction with the low diagnostic ability observed in our study, brings into question the clinical worth of using FOT in cystic fibrosis despite finding that some outcomes can differentiate between health and the disease.Previous analysis using ROC curves by Cuijpers et al, suggestedthat FOT does not have the ability to detect between health and disease 25. In contrast, our data suggests that FOT can identify between health and disease, though the ability of specific FOT outcomes to detect differences depended on the respiratory disease in question.These opposing findings are likely due to our study stratifying children by specific lung disease, whereas the previous analysis did not classify by respiratory disease and instead compared symptomatic versus asymptomatic children with no formal respiratory diagnosis.…”

“…Previous analysis using ROC curves by Cuijpers et al, suggested that FOT does not have the ability to detect between health and disease . In contrast, our data suggests that FOT can identify between health and disease, though the ability of specific FOT outcomes to detect differences depended on the respiratory disease in question.…”

Tidal changes in respiratory resistance are sensitive indicators of airway obstruction in children

“…Respiratory resistance is assumed to reflect airway calibre; therefore, FOT measurements have been employed widely in paediatric studies in various groups of patients with respiratory disease. [23][24][25][26][27][28] While some of these studies suggested that, similarly to other methods, such as spirometry 5 7 and multiple breath washout 29 30 the FOT was able to distinguish between healthy and diseased subject groups, 25 28 31-33 others raised concerns about the diagnostic value of the Zrs data, especially in young children. 23 24 26 27 34 The controversies surrounding the FOT arise from the diversity of Zrs measures reported from the various studies and also from the wide range of the normal values in the paediatric population for any given age or height.…”

Cutting edge technologies in respiratory research: Lung function testing

“…However, there is also evidence of disparity between impedance oscillometry measures and spirometry measures of response during bronchial challenge, which may relate to the population being studied 13 . As a single measurement of airway function, resistance and reactance have been found to differ between groups of children defined by an absence or presence of wheeze or cough, 20,21 although this is not a consistent finding 22 . Differences in impedance parameters have been reported from children with cystic fibrosis or neonatal chronic lung disease 23,24 although again, there is a high degree of overlap in impedance parameters between disease and normality.…”