Can the interrupter resistance be used to measure airway hyperresponsiveness during the methacholine challenge test as a substitute for FEV1?

Abstract

Introduction: The gold standard outcome measure of airway hyperresponsiveness during the methacholine challenge test (MCT) is the provocation dose causing a fall in forced expiratory volume in 1 second (FEV1) ≥ 20%. It is not always feasible for patients to be able to perform acceptable and repeatable FEV1 manoeuvres, implying the need for an easy to perform outcome measure during MCT. Interrupter resistance (Rint) during MCT in children seems to have insufficient capacity to diagnose individual patients[1]. In adults Rint during MCT is less well evaluated.

Methods: FEV1 is assessed in adults referred for MCT at baseline and after inhalation of doubling methacholine concentrations according to the guidelines from the European respiratory society. Rint is measured (Geratherm Respiratory Diffustik) two times: at baseline and after the last dose of methacholine administered. Rint is measured after FEV1.

Results: 28 patients are included of which 11 had a fall in FEV1 ≥ 20% and 17 did not, 60.7% are female and mean age was 49 (range 26-79). There was no significant association between changes from baseline in Rint and FEV1 (rs= -0,04, P= 0,83). The AUC of the ROC curve of Rint versus FEV1 was 0.49.

Conclusions: Rint in adults patients seems to have insufficient capacity to measure airway obstruction during MCT.

Reference

[1] Koopman, M., Brackel, H., Vaessen-Verberne, A., Hop, W., & van der Ent, C. (2010). Evaluation of interrupter resistance in methacholine challenge testing in children. Pediatric Pulmonology, 46(3), 266-271. doi: 10.1002/ppul.21362