A portable device based on the interrupter technique to measure bronchodilator response in schoolchildren

Abstract

A new device for measuring airway resistance following brief airflow interruption (Microlab 4000; Micromedical Ltd, UK) was evaluated in 25 asthmatic school children in comparison with well-established methods.Airway resistance was measured during brief airflow interruption (Rint), before and after administration of salbutamol 200 µg by metered-dose inhaler, and in the spirometric parameters, forced expiratory volume in one second (FEV1) and peak expiratory flow (PEF), and total respiratory system resistance at 6 Hz (Rrs,6) measured by the forced oscillation technique (FOT). The sensitivity index (SI) (mean change/baseline standard deviation) was calculated for each subject.At baseline, interrupter conductance, the reciprocal of Rint, correlated well with FEV1 (r=0.837; p<0.001) and PEF (r=0.773; p <0.001), and Rint correlated highly with Rrs,6 (r=0.942; p<0.001). The median intrasubject coefficient of variation of the interrupter method was higher than the FOT or either spirometric parameter: Rint 11%, Rrs,6 9%, FEV1 5% and PEF 5%. However, the sensitivity to detect change after bronchodilator, expressed as the median SI, did not differ significantly between measurements: Rint 3.5, Rrs,6 3.6, FEV1 2.4 and PEF 3.0. A significant response (SI >2) was shown by the interrupter in 22 of the subjects compared with 16 by FEV1.The interrupter technique is useful for assessing changes in airway calibre in asthmatic school children, with a sensitivity at least as good as standard methods. Such a device could be of particular value in those too young to perform spirometry.

The interrupter technique to assess airway responsiveness in children with cystic fibrosis

“…2 R int is carried out during spontaneous breathing and hence is unlikely to cause glottic narrowing; it requires minimal subject cooperation, is quick, and well tolerated. 3 Based on the assumption that, during tidal breathing, a brief interruption of airflow at the mouth is followed by rapid equilibration of pressure throughout the airways, this technique provides an indirect measure of airways resistance. R int measurements correlate well with other measurements of airways resistance, are no more variable than other measures of lung function in pre-school children and show a close negative correlation with FEV 1 .…”

Measurements of interrupter resistance: reference values for children 3–13 yrs of age

“…Rint measurements have been shown to be reproducible [1,[4][5][6], sufficiently sensitive to detect (sub)clinical airway obstruction [6,7], and to correlate satisfactorily with measurements of airway resistance [4,8,9]. The technique can not only be used as a tool to screen for airway obstruction, but also to assess the responses to bronchodilating and bronchoconstricting agents [1,3,10]. It is especially suitable for preschool children because it only requires passive cooperation.…”

How should airways resistance be measured in young children: mask or mouthpiece?

“…Rint correlates well with other measurements of lung function in normal children [8,11,19], in children with asthma [6,8,15,17] and in children with cystic fibrosis [8]. The correlation between Rint and specific airways resistance measured using a plethysmograph is also good [5], but Rint measurements are potentially affected by the resistance of the lungs and chest wall as much as that of the airways themselves [25].…”

“…As equilibration of mouth and alveolar pressure may occur more slowly in obstructed airways, Rint tends to underestimate airways resistance in children with asthma [6,14]. However, in children aged 5 -15 yrs it has been shown to be as sensitive as spirometry in detecting bronchodilator responsiveness [15]. Rint can now be measured using portable, affordable equipment [8, 10, 12, 15 -18], hereby providing the potential to assess lung function more easily in children v7 yrs.…”