Detection of Inadequately Controlled Asthma in Adults Using Impulse Oscillometry and Fractional Exhaled Nitric Oxide.

Purpose: To investigate the effectiveness of impulse oscillometry (IOS) and its combination with fractional expiratory nitric oxide (FeNO) in distinguishing inadequately controlled asthma (ICA) from well-controlled asthma (WCA) in adults.

Patients and methods: Adult patients aged 18 and above with asthma were recruited and underwent routine blood tests, FeNO, IOS, and spirometry before and after bronchodilator administration on the same day. Asthma control level was assessed using Asthma Control Test (ACT) scores; WCA was defined as a score above 20, while ICA was defined as a score of 20 or below. Receiver operating characteristic curve (ROC) and logistic regression analyses were employed to determine the relationship between IOS and FeNO measurements and asthma control.

Results: The z score values of IOS parameters, specifically resistance at 5 hz (R5), resistance at 20 hz (R20), and the area under reactance curve between 5 hz and resonant frequency (AX) after bronchodilator administration were significantly different between the WCA (n = 75) and ICA (n = 77) groups. IOS parameters, R5, R20, and AX, after bronchodilation identified patients with ICA, with areas under receiver operating characteristic curve (AUC) of 0.654, 0.690, and 0.708, respectively, adjusted for smoke exposure, variable airflow limitation and fixed airflow obstruction. Combining IOS parameters with FeNO significantly increased the AUC (0.728, 0.752, and 0.763) for detecting ICA compared to IOS parameters with R5, R20, and AX, alone. Patients with abnormal IOS and FeNO values had significantly higher odds ratio (OR) of having ICA by logistic regression analyses, especially for abnormally higher AX, with an OR of 6.48.

Conclusion: IOS is useful in discriminating ICA from WCA in adults, with its effectiveness further enhanced when combined with FeNO measurements.