THE MEASUREMENT OF METHACHOLINE RESPONSIVENESS IN 5-YEAR-OLD CHILDREN- 3 METHODS COMPARED

The aim of this study was to compare the feasibility of three techniqu es 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 t ension (Ptco(2)) and the detection of wheeze on auscultation of the ch est. Thirty children aged 5 yrs, with a history of wheeze, and six asy mptomatic controls, took part in a bronchial challenge test using meth acholine administered by Wright nebulizer by the tidal-breathing metho d, The provocative concentration which produced a 35% increase in Rrs6 (PC35Rrs6) and a 15% decreases in Ptco, (PC15PtcO(2)) were determined by interpolation, and the chest was auscultated after each dose of me thacholine. The FOT was found to be unreliable in this age group: in s even children, the data were technically unsatisfactory in the presenc e of induced bronchoconstriction, whilst in three children, changes in Rrs were inconsistent after challenge, The use of Rrs8 did not improv e 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 wa s audible in only 4 of 25 (16%) of the positive and in no negative cha llenges. With this protocol, we found the FOT to be unreliable and the auscultation method valueless and potentially dangerous, since marked falls in PteO(2) of up to 33% sometimes occurred in the absence of wh eeze. The PtcO(2) method seems to be the most technically reliable tec hnique for measuring the response to bronchial challenge in 5 year old children, The underlying pathophysiology and diagnostic value of PC15 Pte(2) values in young children remain to be established.