Background: Impulse oscillometry (IOS); one of the forced oscillation techniques that is a good method for measuring airway resistance without any special breathing skill. This method might reflect different aspects of airway obstruction compared to conventional spirometry. Object: To evaluate airway characteristics of young asthmatics after exercise bronchial provocation test (EBT) using IOS technique Methods: 47 young adults who were recruited to the Korean military service were enrolled. All of them underwent methacholine bronchial provocation test (MBPT) and EBT (10 minutes of treadmill exercise) for their asthma status evaluation. The IOS and spirometry parameters were collected at baseline, immediate-post EBT, 5 min, 10 min, 20 min and 30 min after EBT. Subjects were divided into two groups according to MBPT results (PC20 > 25.0 mg/mL for airway hyperresponsiveness (AHR) absent group (n=12) and PC20 < 12.0 mg/mL for AHR present group (n=35)). Results: There were differences of FEV1 percent falls between two groups at 5 min (+0.12% vs-9.96%, p<0.001), 10 min (+1.28% vs-7.45%, p=0.002) and 20 min (+1.01% vs-3.41%, p=0.011) after exercise. Resistance at 5 Hz (R5); one of the IOS parameter, was higher in the AHR present group than AHR negative group at 5 min (0.018 kPa/L/sec vs 0.071 kPa/L/sec, p=0.027) and 10 min (-0.007 kPa/L/sec vs 0.055 kPa/L/sec, p=0.001) after exercise. Airway reactance (AX); integration of reactance (X) from 5 Hz to resonance frequency was also increased in AHR present group at 5 min (0.091 kPa/L vs 0.431 kPa/L, p=0.010) and 10 min (0.007 kPa/L vs 0.298 kPa/L, p=0.032) after exercise. Frequency dependency of airway resistance (R5-R20) and Resistance at 10 Hz (R10) values were increased too. Low-frequency reactance at 5 Hz (X5) was more decreased in AHR present group than absent The FEV1 percent fall was well-correlated with the changes of R5 at 5 min (r=-0.314, p=0.032), R5 at 10 min (r=-0.367, p=0.011), AX at 5 min (r=-0.545, p<0.001) and AX at 10 min (r=-0.441, p=0.002) after exercise. Conclusions: These results suggested that IOS parameters especially R5 and AX can be useful for understanding of exercise induced airway characteristics of young asthmatics.

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