A Comparison of Impulse Oscillometry to Spirometry in the Evaluation of Exercise Induced Bronchoconstriction in Children with Asthma

Abstract

Rationale: Impulse Oscillometry (IOS) is a noninvasive method to measure respiratory impedance. The use of IOS as an indirect measure of airflow obstruction compared to spirometry in the evaluation of Exercise-Induced Bronchoconstriction (EIB) has not been fully explored in children. In this study we aim to describe the IOS values, resistance at 5 Hz (R5rs) in subjects with EIB and without EIB. We also aim to compare whether IOS variables correlate with spirometry variables following exercise challenge test in asthmatic subjects. Methods: We designed a cross sectional study involving subjects between 6-18 years old with a diagnosis of asthma who were referred to the pediatric pulmonary function lab for an exercise challenge test to rule out EIB. Spirometry and IOS were performed at baseline and at 5 minute intervals up to 20 minutes post exercise and again post bronchodilator. Results: 43 subjects were enrolled. Of the 43 subjects, 15 had a 10% fall in FEV1 after exercise significant for EIB. Demographic characteristics (gender, age and ethnicity) were not different comparing subjects with EIB to those without EIB. There was a significant correlation between spirometry and IOS measurements at baseline, 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes and post bronchodilator after exercise (r= -0.75, -0.72, -0.72, -0.76, -0.75, -0.72 and -0.75 respectively, p<0.01) in asthmatic subjects without EIB. In asthmatic subjects with EIB, there was a significant correlation between spirometry and IOS measurements at baseline, 1 minute, and post bronchodilator after exercise (r=-0.55, -0.79 and -0.63 respectively p<0.05). There was weak correlation between spirometry and IOS measurements at 5 minutes, 10 minutes, 15 minutes and 20 minutes after exercise for asthmatic subjects with EIB. Conclusion: A significant correlation was found between spirometry and IOS measurements of change in airway function in asthmatic patients both with EIB and without EIB.