Impulse oscillometry: An adjunct or alternative to spirometry in the diagnosis of obstructive airway disease. Results from an observational study

BACKGROUND: Obstructive airway disease is one of the leading causes of morbidity and mortality in India. Spirometry is the gold standard for diagnosis of OAD, but is difficult to perform and requires patient cooperation. Impulse oscillometry has been shown to be more sensitive in diagnosis of OAD in studies conducted outside India. MATERIALS AND METHODS: This was a cross sectional, observational study including 125 (63 asthma and 62 COPD) patients conducted at a tertiary care centre. All patients underwent spirometry and impulse oscillometry and parameters were compared. RESULTS: Patients with asthma were significantly younger (p < 0.001), predominantly female (p < 0.001), had a history of allergy (p < 0.001) and a family history of OAD (p < 0.001). COPD patients were significantly older, male, smokers (p < 0.001) and had a history of COVID-19 disease (p < 0.001). Upon comparing lung function, COPD patients in our study had significantly lower post FEV1/FVC% (p = 0.001) and PEFR (p = 0.006) and significantly higher R5 (p = 0.008), R5-R20 (p = 0.046) and AX (p = 0.014) in comparison to asthma patients. We found that increased small airway resistance (SAD) is associated with reduced lung function in both the groups. We found expiratory flow limitation (EFL) in 72.6% COPD patients. Using 40% decrease in X5 as a criterion, we identified a significantly higher number of patients with bronchodilator responsiveness (P < 0.001). CONCLUSION: R5, R5-R20 and AX can be used to differentiate between asthma and COPD. SAD is associated with reduced lung function in both group of patients. IOS parameters are more sensitive in diagnosis of bronchodilator responsiveness.