Long-term variability of impulse Oscillometry and Spirometry in stable COPD and Asthma

Abstract Background: While optimizing spirometry is a challenge for all lung function labs, long-term variability is not known in stable COPD (chronic obstructive pulmonary disease) and chronic asthma. The forced oscillation technique is increasingly employed in routine lung function testing. Our aim in this study was to determine the variability in oscillometric parameters between clinic visits over weeks or months in two patient groups during a period of clinical stability (asthma patients and COPD patients). Moreover, the research assesses relationships between IOS (impulse oscillometry) parameter long-term variability and COPD severity.Methods: We used data from 73 patients with stable COPD and 119 patients with stable asthma at the Shanghai Pulmonary Hospital Affiliated to Tongji University. Patients were included if they had three or more clinic visits where spirometry and IOS were performed during a clinically stable period. Only data recorded from the first three visits were used. The standard deviation (SDbv), the coefficient of variation (COV), intraclass correlation coefficient (ICC) and the coefficient of repeatability (COR) were calculated, Wilcoxon Mann-Whitney test was used for data that did not conform to normality of distributions, Kruskal Wallis test was used to compare with multiple groups, post hoc comparison was analyzed by Bonferroni, Spearman correlation coefficients for non-parametric data, the multiple regression analyses to determine the relationship between long-term variability and airflow obstruction.Results: 1. the repeatability of IOS parameters were high (>0.80) ICC values in COPD and asthma, ICC values of IOS parameters were higher than for spirometry; 2. repeatability (ICC valve<0.8) of spirometry parameters was lower than IOS parameters (ICC valve>0.8) in different GOLD (the Global Initiative for Chronic Obstructive Lung Disease) stage, and the higher the stage, the worse the repeatability; 3. the severity of airflow obstruction was correlated with long-term variability of R5 (R at 5 Hz) (P<0.05) and R5-R20 (P<0.05), not with long-term variability of R20 (R at 20 Hz) (P>0.05).Conclusion: IOS parameters have good long-term repeatability in asthma and COPD. Additionally, variability is different between diseases and GOLD stages, repeatability of spirometry parameters is lower than that in IOS parameters in different GOLD stages. The greater the long-term variability seen in COPD is associated with airflow obstruction.