Methacholine challenge in young children as evaluated by spirometry and impulse oscillometry.

Background: In young children, it is difficult to obtain a reproducible flow-volume curve throughout all stages of bronchial challenge. The forced oscillation technique (FOT) is especially established in paediatrics because this method does not require forced or maximal manoeuvres and is less cooperation-dependent than conventional spirometry.

Objectives: To evaluate the association of spirometric and impulse oscillometric (IOS) indices in a short protocol for methacholine provocation.

Methods: The primary endpoint was the methacholine dose that caused a 20% decrease in FEV(1) (PD(-20)FEV(1)) compared to baseline. Changes in respiratory resistance (Rrs5) and reactance (Xrs5) acquired by IOS were compared with FEV(1).

Results: Forty-eight children (5.3 ± 0.9 years) were challenged. The mean maximal reduction in FEV(1) was 29.8% ± 14.7 (p < 0.0001), the mean increase in Rsr5 was 55.3% ± 31.7, and the mean decrease in Xrs5 was 0.37 kPa s L(-1) ± 0.23 (p < 0.001). An increase in Rrs5 of 45.2% and a decrease in Xrs5 of 0.69 kPa s L(-1) showed the optimal combination of sensitivity and specificity to detect a 20% reduction in FEV(1) (0.72 and 0.73; 0.80 and 0.76, respectively), and the area under the ROC curve was 0.76 and 0.81, respectively (p < 0.005). In 28 patients with significant changes in FEV(1) and Rsr5, the PD(-20)FEV(1) was 0.48 mg methacholine ±0.59 and the PD(+40)Rrs5 was 0.28 mg methacholine ±0.45 (p = 0.03).

Conclusions: A short protocol for methacholine challenge testing is feasible in young children. IOS detected 70-80% of patients who responded in spirometry. During the challenge, the Rrs5 response preceded the FEV(1) response.