Assessing Asthma Control by Impulse Oscillometry and Fractional Expiratory Nitric Oxide in Children With Normal Spirometry

Background Because spirometric parameters fail to address current status of asthma in some patients, additional tests are required for better evaluation of asthma. Objective We aimed to test the ability of impulse oscillometry (IOS) and fractional expiratory nitric oxide (FeNO) in identifying inadequately controlled asthma (ICA) that was not uncovered by spirometry. Methods Recruited asthmatic children between ages of 8 and 16 years underwent spirometry, IOS, and FeNO measurements on the same day. Only subjects who had spirometric indices within normal range were included. Asthma Control Questionnaire-6 scores of 0.75 or lower and greater than 0.75 indicated well-controlled asthma (WCA) and ICA. Percent predicted values of IOS parameters and IOS reference values for upper and lower limits of normal (>95th and <5th percentiles, respectively) were calculated on the basis of previously published equations. Results There were no significant differences in all spirometric indices between the WCA (n = 59) and the ICA (n = 101) groups. The % predicted values of IOS parameters except resistance at 20 Hz (R20) were significantly different between the 2 groups. Receiver operating characteristic analysis showed that the highest and lowest areas under the curve were 0.81 and 0.67 for the difference between the resistances at 5 Hz and 20 Hz (R5–R20) and R20 in discrimination of ICA versus WCA. The areas under the curve for IOS parameters were improved by combination with FeNO. The better discriminative ability of IOS was also supported by the higher values of the concordance index for the resistance at 5 Hz (R5), R5–R20, the reactance at 5 Hz (X5), and the resonant frequency of reactance than those for spirometric parameters. Compared with those with normal values, subjects with abnormal IOS parameters or high FeNO had significantly higher odds of having ICA. Conclusions The IOS parameters and FeNO were shown to be useful in identifying children with ICA when spirometry was normal. Because spirometric parameters fail to address current status of asthma in some patients, additional tests are required for better evaluation of asthma. We aimed to test the ability of impulse oscillometry (IOS) and fractional expiratory nitric oxide (FeNO) in identifying inadequately controlled asthma (ICA) that was not uncovered by spirometry. Recruited asthmatic children between ages of 8 and 16 years underwent spirometry, IOS, and FeNO measurements on the same day. Only subjects who had spirometric indices within normal range were included. Asthma Control Questionnaire-6 scores of 0.75 or lower and greater than 0.75 indicated well-controlled asthma (WCA) and ICA. Percent predicted values of IOS parameters and IOS reference values for upper and lower limits of normal (>95th and <5th percentiles, respectively) were calculated on the basis of previously published equations. There were no significant differences in all spirometric indices between the WCA (n = 59) and the ICA (n = 101) groups. The % predicted values of IOS parameters except resistance at 20 Hz (R20) were significantly different between the 2 groups. Receiver operating characteristic analysis showed that the highest and lowest areas under the curve were 0.81 and 0.67 for the difference between the resistances at 5 Hz and 20 Hz (R5–R20) and R20 in discrimination of ICA versus WCA. The areas under the curve for IOS parameters were improved by combination with FeNO. The better discriminative ability of IOS was also supported by the higher values of the concordance index for the resistance at 5 Hz (R5), R5–R20, the reactance at 5 Hz (X5), and the resonant frequency of reactance than those for spirometric parameters. Compared with those with normal values, subjects with abnormal IOS parameters or high FeNO had significantly higher odds of having ICA. The IOS parameters and FeNO were shown to be useful in identifying children with ICA when spirometry was normal.