Correlation between impulse oscillometry with bronchodilator reversibility in asthmatic population in a tertiary referral centre.

Introduction: Spirometry is considered as a 'gold standard' for diagnosis of asthma. Impulse oscillometry (IOS) is an alternative diagnostic tool which requires less cooperation by the participants. We performed a study to determine the correlation of IOS with bronchodilator reversibility from spirometry in asthmatic participants. We studied the correlation between forced expiratory flow (FEF) and differences between the resistance at 5Hz and 20Hz (R-R) in small airway disease (SAD) and the proportion of SAD diagnosed using IOS.

Materials And Methods: This was a cross-sectional study involving 82 asthmatic participants in Hospital Canselor Tuanku Muhriz (HCTM), Universiti Kebangsaan Malaysia (UKM) conducted between December 2020 till January 2022. Participants performed pre- and post-bronchodilator IOS and spirometry within the same day. Correlation between spirometry and IOS parameters and FEF with IOS were determined and analysed.

Results: The change of forced expiratory volume in 1 second (FEV1) was statistically correlated with a change of R5 in IOS. A decrement of 14.5% in R5 can be correlated with positive bronchodilator response (BDR) with a sensitivity of 63.9% and specificity of 60.9%, p=0.007. Pre-bronchodilator FEF correlated with all parameters of SAD in IOS, e.g., R-R, reactance at 5Hz (X5) and area of reactance (AX), p < 0.05. IOS detection for SAD is higher compared to FEF in the BDR negative group (91.3% vs 58.7%).

Conclusion: IOS detected both bronchodilator reversibility and SAD hence can be considered as an alternative tool to spirometry for diagnosis of asthma in adults. IOS detected SAD more than FEF, especially in BDR-negative group.