Impulse oscillometry for leukotriene D4 inhalation challenge in asthma

BACKGROUND: The value of impulse oscillometry (IOS) for bronchial provocation testing is poorly defined. We investigated the positive threshold derived from the parameters and diagnostic power of IOS for asthma with the leukotriene D4 bronchial provocation test. METHODS: We enrolled 62 subjects with asthma and 21 healthy subjects. IOS was employed to perform the leukotriene D4 bronchial provocation test, followed by spirometry. The positive threshold was determined based on the cutoff point in the receiver operating characteristic curve, from which the parameters with the highest diagnostic power were obtained. RESULTS: Airway impedance at 5 Hz (Z5), resistance at 5 Hz (R5), and resonance frequency had the highest diagnostic power (areas under curve 0.82, 0.82, and 0.81, respectively), with increases of 57%, 43%, and 63%, corresponding to a 20% decrease in FEV1, respectively. IOS indices yielded assay sensitivity and specificity similar to that of spirometry. The positive threshold for IOS, defined as either a 57% increase in Z5 or a 63% increase in resonance frequency in the bronchial provocation test, yielded an assay accuracy of 0.6 in subjects with asthma. CONCLUSIONS: IOS during the leukotriene D4 bronchial provocation test has a diagnostic power similar to that of spirometry. Either a 57% increase in Z5 or a 63% increase in resonance frequency may be regarded as a surrogate of FEV1 decrease to determine airway hyper-responsiveness in asthma.