The aim of this study was to compare the feasibility of three techniques for measuring the response to bronchial challenge in young children: a direct airway measurement, the forced oscillation technique (FOT) for determining respiratory system resistance at 6 and 8 Hz (Rrs6 and Rrs8), and two indirect methods, the change in transcutaneous oxygen tension (PtcO 2 ) and the detection of wheeze on auscultation of the chest. Thirty children aged 5 yrs, with a history of wheeze, and six asymptomatic controls, took part in a bronchial challenge test using methacholine administered by Wright nebulizer by the tidal-breathing method. The provocative concentration which produced a 35% increase in Rrs6 (PC35Rrs6) and a 15% decreases in PtcO 2 (PC15PtcO 2 ) were determined by interpolation, and the chest was auscultated after each dose of methacholine.The FOT was found to be unreliable in this age group: in seven children, the data were technically unsatisfactory in the presence of induced bronchoconstriction, whilst in three children, changes in Rrs were inconsistent after challenge. The use of Rrs8 did not improve the detection of positive responses. PC15PtcO 2 was measurable in 29 of 30 children, and in 18 of these PC35Rrs6 was also measurable. In no subject did a significant, sustained increase in Rrs occur during challenge in the absence of a significant change in PtcO 2 . Wheeze was audible in only 4 of 25 (16%) of the positive and in no negative challenges.With this protocol, we found the FOT to be unreliable and the auscultation method valueless and potentially dangerous, since marked falls in PtcO 2 of up to 33% sometimes occurred in the absence of wheeze. The PtcO 2 method seems to be the most technically reliable technique for measuring the response to bronchial challenge in 5 year old children. The underlying pathophysiology and diagnostic value of PC15PtcO 2 values in young children remain to be established.

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The importance of this study is the confirmation, within important statistical guidelines for a study of reproducibility, that the methods examined are reproducible and valid.

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Airway resistance and atopy in preschool children with wheeze and cough. S.A. McKenzie, P.D. Bridge, M.J.R. Healy. #ERS Journals Ltd 2000. ABSTRACT: The extent to which the measurement of airways resistance by the interrupter technique (Rint) distinguishes preschool children with previous wheeze from those with no respiratory symptoms and helps to classify subjects with persistent cough, was investigated.Rint was measured before and after salbutamol treatment in 82 children with recurrent wheeze, 58 with isolated cough and 48 with no symptoms (control subjects). Their mean age (range) was 3.7 yrs (2±<5 yrs).Median baseline Rint was higher (p<0.0001) in wheezers than in either coughers or control subjects (1.16, 0.94 and 0.88 kPa . L -1 . s -1 respectively); coughers did not differ significantly from control subjects (p=0.14). The median ratios of baseline to postsalbutamol measurements (bronchodilator response (BDR)) in the groups differed significantly (1.40, 1.27 and 1.07, p#0.01 for all), suggesting that coughers occupy an intermediate position. A BDR ratio of >1.22 had a specificity and sensitivity for wheeze of 80% and 76% respectively. Twenty-eight coughers had a BDR ratio >1.22. Wheezers' immunoglobulin E was inversely related to baseline Rint.It is concluded that measurements of airway resistance by the interrupter technique are useful for classifying preschool children with respiratory symptoms and could be used to monitor the effect of interventions. The relation between atopy and airways resistance suggests that they have separate roles in preschool wheezing. Coughers with a high bronchodilator response could represent "cough-variant" asthma in children who have baseline airway resistance by the interrupter technique measurements similar to control subjects. Whether these children develop classical asthma will only be known at follow-up later in childhood. Eur Respir J 2000; 15: 833±838.