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 (R_int) 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 R_int and FEV₁ were studied. A receiver operating characteristic (ROC) curve was used to describe sensitivity and specificity of R_int. 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 R_int with increasing methacholine doses. However, individual changes of R_int showed large fluctuations. There was great overlap in change of R_int 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 R_int to diagnose BHR in individual patients seems limited. Pediatr Pulmonol. 2011; 46:266–271. © 2011 Wiley‐Liss, Inc.