Forced Oscillation Technique May Identify Severe Asthma

Background: Fixed airflow obstruction in severe asthma is usually assessed by spirometry. However, the role of the forced oscillation technique (FOT) in severe asthma is unknown. We hypothesised that FOT would be useful to diagnose severe asthma and discriminate it from non-severe asthma. Aims: In this cross-sectional study, we assessed the usefulness of FOT in diagnosing severe asthma. Methods: FOT (MostGraph) was performed in 48 patients with severe asthma and 207 with non-severe asthma who attended outpatient clinics at Shizuoka General Hospital or Nihon University Itabashi Hospital for routine check-ups between February 2013 and August 2016. Severe asthma patients fulfilled the definition of ERS/ATS severe asthma guidelines. Recursive partitioning analysis was performed to create classification tree. Demographic data, peripheral blood eosinophil and neutrophil counts, IgE, serum periostin, YKL-40, fractional exhaled nitric oxide, and spirometry were compared between the classes. Results: Recursive partitioning analysis revealed that resonant frequency (Fres: Hz) and resistance at 5 Hz (R5: cmH2O/L/s) were the significant parameters, suggesting the presence of airflow obstruction during tidal breathing (Figure 1). The accuracy of the diagnosis of severe asthma (class 4) was as follows: diagnostic odds ratio, 16.8; 95% confidence interval, 6.1 to 46.0; sensitivity 33.3%; and specificity, 97.1%. The patients in class 4 had lower FEV1, FVC, and FEV1/FVC, and higher BMI and YKL-40 than those in class 1. However, there was no difference in other parameters between classes 4 and 1. Conclusions: FOT may be useful in identifying severe asthma.