Evaluation of interrupter resistance in methacholine challenge testing in children.

Bronchial hyperresponsiveness (BHR) is a key feature of asthma and is assessed using bronchial provocation tests. The primary outcome in such tests (a 20% decrease in forced expiratory volume in 1 sec (FEV1)) is difficult to measure in young patients. This study evaluated the sensitivity and specificity of the interrupter resistance (Rint ) technique, which does not require active patient participation, by comparing it to the primary outcome measure. Methacholine challenge tests were performed in children with a history of moderate asthma and BHR. Mean and individual changes in Rint and FEV1 were studied. A receiver operating characteristic (ROC) curve was used to describe sensitivity and specificity of Rint . Seventy-three children (median age: 9.2 years; range: 6.3-13.4 years) participated. There was a significant (P < 0.01) increase in mean Rint with increasing methacholine doses. However, individual changes of Rint showed large fluctuations. There was great overlap in change of Rint between children who did and did not reach the FEV1 endpoint. A ROC curve showed an area under the curve of 0.65. Because of low sensitivity and specificity, the use of Rint to diagnose BHR in individual patients seems limited.