Forced oscillatory technique R5-19 values correlate with spirometry FEV1/FVC in severe eosinophilic asthma. An observational, prospective, cohort study.

INTRODUCTION

Severe asthma affects 3-10 % of asthmatic patients. Biologic therapies can act as disease modifying agents in severe asthma. The prevalence of small airways dysfunction (SAD) increases with asthma severity. Forced Oscillatory Technique (FOT) is a reliable method for studying small airways. The aim of the study was to analyze FOT parameters in a cohort of eosinophilic severe asthma patients naïve of biologic therapy, and to describe the presence of correlation with spirometry data. Variations of FOT parameters after 6 and 12 months from the start of biologic therapy were also prospectively recorded and analyzed.

METHODS

47 severe eosinophilic asthma patients were consecutively enrolled. FOT, spirometry data, levels of asthma biomarkers, number of exacerbations, Asthma Control Test (ACT) were determined at baseline (T0: patients naïve of biologic treatment) and after 6 and 12 months.

RESULTS

at T0, a significant linear correlation was found between R5-19 and FEV1/FVC (Forced expiratory volume in 1 s/Forced Vital Capacity) values (p = 0.0008). At T0, FOT R5-19 values were more elevated in obstructed patients. The cut-off value of R5-19 that best discriminates the presence of obstruction (FEV1/FVC <0.70) was determined at 0.81 cmHO/(L/s) (sensitivity 0.58, specificity 0.76, ROC-AUC 0.67). A significant relationship was found between FEV1/FVC and FOT R5-19 also after 6 (p = 0.007) and 12 months (p = 0.027) of biologic therapy. No significant correlations were found between any other FOT parameter and blood eosinophils count, FeNO, number of exacerbations or ACT.

CONCLUSIONS

FOT R5-19 values correlate with FEV1/FVC and are significantly higher in obstruction. This correlation could be explained by the higher resistances of small airways in obstructed patients.