INTRODUCTION: The reference standard for diagnosis of obstructive airways disease is spirometry, which is patient-effort and technician-skill dependent. Forced Oscillation Technique (FOT) uses tidal breathing, and might be more sensitive at detecting small airways disease and early disease. However, normative values have been defined for specific populations, and might differ across the world.

AIMS AND OBJECTIVES: To compare test parameters for FOT among healthy Indian adults with published norms.

METHODS: Consecutive subjects ? 18 years with no diagnosed respiratory illness undergoing spirometry as part of routine health screening were enrolled. Consenting subjects underwent FOT using the Thorasys Tremoflo C-100 device.

RESULTS: 200 participants, 63% male, median age 51 (IQR 42-58), median BMI 26.78 (IQR 24.36-29.75) were enrolled. As compared to the suggested reference norms (Oostveen et al), Indians (both men and women) had a statistically significantly higher resistance at 5Hz (R5) and 20 Hz (R20) frequency, and reactance at 5 Hz (X5) frequency.

CONCLUSION: Larger studies, and correlation with imaging modalities and health status are needed to define the normative values for FOT to prevent misclassifying healthy individuals as being abnormal.

Reference: Oostveen E,et al. Respiratory impedance in healthy subjects: baseline values and bronchodilator response. Eur Respir J. 2013 Dec;42(6):1513-23.[figure1]