Utility of Forced Oscillation Technique in Detecting Obstruction in Asthma and the Significance of ‘Isolated Increase in R5-R20’ (II R5-R20)

Document Type : Original Article

Author

Head of the Department of Pulmonary and Sleep Medicine, MOSC Medical Mission Hospital, Thrissur, Kerala, India.

Abstract

Introduction & objective : The objective of this retrospective observational study was to investigate the role of forced oscillometry in detecting airway obstruction in asthma and to compare its sensitivity to that of spirometry in detecting airway obstruction.
Method: The retrospective observational study was conducted in the Pulmonary Medicine Department of a secondary hospital in South India. Data from diagnosed cases of asthma from  October 1, 2024, to March 31, 2025, were collected and analyzed to determine the effectiveness of forced oscillometry in detecting airway obstruction in asthma compared to spirometry. Diagnosis of asthma was made by the treating pulmonologist based on history, examination, and investigations. The cohort included patients over eighteen years of age who underwent both oscillometry and spirometry. Patients who only had one of the tests done were excluded from the study. Asthma-COPD overlap syndromes were also excluded.
Results: The total number of patients in the cohort was 182 with a mean age of 48.5 years. Spirometry showed obstruction in 36.8% of diagnosed asthma cases, while forced oscillometry detected obstruction in 69.7% of cases (p < 0.0001, 95% CI 20%–46%, RR-1.89). When both spirometry and oscillometry were combined, the sensitivity for detecting underlying airway obstruction increased to 80.8% (n = 147). Isolated increase in R5-R20 (II R5-R20) was observed in 36.81% of the cohort, whit this phenomenon seen in 52.5% of cases where oscillometry was more successful than spirometry.
Conclusion: Oscillometry is more sensitive than spirometry in detecting airway obstruction in asthmatics. Using both methodsIt for evaluation increases sensitivity. ‘II R5-R20’ is defined as an increase in R5-R20 with a normal R5 and is the most sensitive parameter for detecting airway disease in asthmatics. It may detect the early changes in airway resistance, making it useful  for identifying airway obstruction at an earlier stage.

Keywords

References

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Journal of Cardio-Thoracic Medicine
Volume 14, Issue 1
March 2026
Pages 1656-1661

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