Lung oscillometry indices are impaired in healthy smokers and biomass smoke exposed subjects despite normal spirometry

Introduction: Oscillometry is a simple to perform lung function test with additional benefits of being more sensitive to picking up small airway’s obstruction. We aimed to study lung oscillometry indices among non-smoker, smoker and biomass smoke exposed subjects with normal spirometry from a randomly selected community in rural India. Methods: 16 non-smoker (all males), 12 smoker (all males) and 15 biomass smoke exposed (all females) subjects having normal spirometry (FEV1 and FVC both >80% predicted) were randomly selected from a rural population in India. Oscillometry was performed using Impulse oscillometer (Jaeger, Vyasis, USA), according to ERS standards. The proportion of subjects showing abnormal R5, R5-R20, X5 and AX values were obtained. The cut-off values used for R5 was >0.4 kPa/L/sec, for R5-R20 was <0.1 kPa/L/sec, X5 was <-0.1 kPa /L/sec and AX was >0.4 kPa /L. Results: The mean FEV1 and FVC values for healthy non-smokers, healthy smokers and healthy biomass smoke exposed subjects were 91% ± 7.9, 94% ± 23.6, 96.3% ± 11.2 and 97.2% ± 12.5, 97.1% ± 18 and 103.4% ± 11 respectively. The figure 1. below shows the proportion of subjects with abnormal oscillometry indices in the three groups. Reactance indices (X5 and AX) were predominantly abnormal among biomass smoke exposed subjects, despite having normal spirometry. Conclusion: Abnormal oscillometry indices (R5, R5-R20, X5 and AX) were seen in a significantly large number of healthy subjects, especially among those exposed to biomass smoke. Oscillometry is more sensitive in detecting lung function abnormalities than spirometry. Oscillometry may help diagnose early COPD in the absence of abnormal spirometry.