Measurement of airway resistance using the interrupter technique in preschool children in the ambulatory setting. P.D. Bridge, S. Ranganathan, S.A. McKenzie. #ERS Journals Ltd 1999. ABSTRACT: This study describes the feasibility, repeatability, and interrater reliability of the measurement of airway resistance by the interrupter technique (Rint) in children 2±5 yrs of age, and examines whether reversibility to bronchodilator can be demonstrated in wheezy children.The mean of six Rint values was taken as a measurement. If subjects could complete one measurement and then a second 15 min after bronchodilator, baseline testing and reversibility testing were considered feasible. To measure repeatability, two measurements 30 s apart and measurements before and 15 min after placebo bronchodilator were compared. Measurements by two testers were compared for interrater reliability. Change in Rint in wheezy children was measured after bronchodilator.Fifty-six per cent of 2±3-yr-olds (n=79), 81% of 3±4-yr-olds (n=104) and 95% of 4± 5-yr-olds (n=88) completed baseline testing, and 53%, 71% and 91% completed reversibility testing. Baseline measurements were 0.47±2.56 kPa . Asthma is considered to reflect reversible airways disease. A precise definition his yet to be agreed. It is one of the few organic diseases where diagnosis and treatment are often made only on the parental reporting of symptoms [1], one of which is wheeze. Although there is an assumption that parents know what wheeze is, the history is sometimes vague and often there are no physical signs. In schoolchildren, reversibility of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) to bronchodilator treatment can be measured [2] so that, in cases where the history is not clear, objective measurements can be made. Changes in expiratory flow in infants in response to bronchodilator can be measured [3]. There are no readily available lung function tests suitable for children aged between 18 months and 5 yrs.The measurement of respiratory resistance in young and uncooperative subjects using the forced oscillation technique (FOT) and the interrupter technique (Rint) has been evaluated by several laboratories since the 1980s [4±7]. The simplicity of use for the patient and smaller size of the Rint device make it attractive for use in children aged 2±5 yrs in the ambulatory setting. Respiratory resistance is measured during quiet tidal breathing and requires minimal cooperation on the part of the subject.The theoretical background has been well described [5,6] along with the technical aspects in older children [7]. Although the technique has been tried in a small group of selected preschool children [6], very little has been published on the practicalities of using Rint in an ambulatory setting. In contrast to spirometry, only minimal comprehension and co-ordination are needed for Rint. This means that even acutely ill or tired children, of all ages, should be able to undertake the test successfully. There is no evidence that either bronchoco...

Background and Aims: The measurement of airway resistance using the interrupter technique (R int ) is feasible in preschool children and other subjects unable to undertake spirometry. This makes it potentially useful for the measurement of lung function in these groups. Commercial devices use different algorithms to measure pressure and flow from which R int is derived. This study provides normative values for British children using devices from a single manufacturer. Methods: R int was measured in 236 healthy children of three ethnic groups (Afro-Caribbean and black African, Bangladeshi, and white British) aged 2-10 years using Micro Medical devices. Software in the devices calculated R int from pressure measured by the two point, back extrapolation method from the pressure transient during valve closure, with flow measured just before valve closure. Results: R int is related to both age and height, but when age is allowed for there is not a significant relation with height. Neither gender nor any of the ethnicities studied was significantly related to R int . Discussion: These measurements in healthy children using this technique may be used as reference data for similar populations.

Background: To be able to interpret any measurement, its repeatability should be known. This study reports the repeatability of airway resistance measurements using the interrupter technique (Rint) in children with and without respiratory symptoms. Methods: Children aged 2-10 years who were healthy, had persistent isolated cough, or who had previous wheeze were studied. On the same occasion, three Rint measurements were made 15 minutes apart, before and after placebo and salbutamol given in random order. Results from those given placebo first were analysed for within-occasion repeatability. Between-occasion repeatability measurements were made 2-20 weeks apart (median 3 weeks). Results: For 85 pairs of measurements before and after placebo the limits of agreement were 20% expected resistance and were unaffected by age or health status. The change in resistance following bronchodilator in one of 18 healthy children, 12 of 28 with cough, and 22 of 39 with wheeze exceeded this threshold. For between-occasion measurements the limits of agreement were 32% in 72 healthy subjects, 49% in 57 with cough, and 53% in 95 with previous wheeze. Conclusion: The measurement of airways resistance by the interrupter technique is clinically meaningful when change following an intervention such as the administration of bronchodilator is greater than its within-occasion repeatability. Between-occasion repeatability is too poor to judge change confidently.

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.