The measurement of methacholine responsiveness in 5 year old children: three methods compared.

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 (PtcO2) 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 PtcO2 (PC15PtcO2) were determined by interpolation, and the chest was ausculated 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. PC15PtcO2 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 PtcO2. 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 PtcO2 of up to 33% sometimes occurred in the absence of wheeze.(ABSTRACT TRUNCATED AT 250 WORDS)