It is now well established that SAD precedes the development of obstructive airway diseases (OADs). Spirometry, the gold standard for diagnosis of OADs, is unable to detect SAD. The Oscillometer, is a sensitive tool and corrleates well with presence of SAD in OADs. We aimed to explore the utility of the oscillometer as a diagnostic tool in patients presenting with respiratory symptoms and normal spirometry.

In this single-centre, retrospective, observational study, the forced oscillometry (FOT) readings of 150 consecutive patients who presented with respiratory symptoms but had no evidence of obstruction on Spirometry (FEV1/FVC<0.7) were analysed. The correlation between spirometric and FOT parameters were tested.

The average age of the patients was 48.65+16.14 yrs; 58% were males and 27% had a smoking history. With MMEF (FEF25-75%pred) < 65%, SAD was detected in 35 patients (23%)^1,2. Assuming cut-off > 0.7138 kPa/Ls for R5-R20, SAD was detected in 119 patients (79%)^2,3. The correlation between MMEF and R5-R20 was statistically significant and of moderate degree (r= -0.273, p<0.05). With a cut-off >4.487 for AX^2,3, SAD was detected in 147 patients (98%) and with cut-off >8, 133 in (89%) patients. The correlation between MEF50 and MEF75 (%pred) and FOT parameters and MMEF with AX was of moderate degree.

Overall, our findings indicate that patients with no obstruction on spirometry but presenting with respiratory symptoms may have SAD which can be detected by performing Oscillometry.

(1. Knox-Brown et al. Repir Res 2022; 23:67.; 2. Chui HY et al. JACI Pract 2020; 8- 229-35 E2.; 3. Hsiao Y et al. Am J Respir Crit Care Med 2019;199: A5779)