Forced oscillation technique as a predictor of airway hyper-responsiveness in asthma

Introduction: Airway hyper-responsiveness (AHR) is a cardinal feature of asthma. In a continuous methacholine challenge test (MCT) using Astograph (Chest, Tokyo, Japan), AHR is measured by the methacholine respiratory system resistance dose-response curve. However, information regarding the relationship between AHR and the broadband frequency forced oscillation technique (FOT) is limited. Aims and objective: To investigate the relationship between AHR and the FOT parameters. Methods: Subjects included 37 patients with asthma. AHR and FOT parameters were measured with Astograph and MostGraph (Chest, Tokyo, Japan), respectively. FOT, spirometry, and fractional exhaled nitric oxide (FeNO) were performed before MCT. We used the value of the cumulative dose of inhaled methacholine measured at the inflection point at which respiratory conductance starts to decrease (Dmin) as an index of AHR. This variable was measured in terms of a unit defined as a 1-minute inhalation of methacholine (1 mg/ml). We defined Dmin less than 10 units as AHR. Results: Dmin correlated with inspiratory respiratory system resistance at 5 Hz (R5), 20 Hz (R20), low-frequency area (ALX) and FeNO before MCT (r=-0.495, -0.489, -0.367 and -0.383, respectively). An ROC curve analysis to identify AHR revealed that the area under the curve of R5 (0.741) was larger than those of other parameters. Conclusions: R5, a forced oscillatory parameter, before MCT predicts AHR.