Impulse Oscillometry Detects Small Airway Dysfunction in 61.7% of Asthma Patients With Normal Spirometry, Study Finds
A recent study published in the Indian Journal of Allergy, Asthma and Immunology in July 2026 highlights the superior sensitivity of passive, effort-independent lung function testing, which detected peripheral airway impairment in 61.7% of asthmatic patients with completely normal spirometry.
While effort-dependent spirometry remains challenging, Indian-specific diagnostic thresholds for passive impulse oscillometry (IOS) are scarce. Addressing this gap, Aanchal S. Malik, Bharati K. Italiya, Ravindra Shinde, and Sushama R. Dugad from Ahmedabad and Nashik established local IOS cutoffs and evaluated their correlation with spirometry and asthma control.
Therefore, the cross-sectional, observational, diagnostic test accuracy study was conducted over two years (August 2022 to August 2024) at a Western Indian tertiary care center, comparing pre- and post-bronchodilator spirometry (performed fifteen minutes after inhaling two hundred micrograms of salbutamol) with multi-frequency impulse oscillometry in 100 asthmatic patients aged 5 to 45 years. Excluding patients with acute exacerbations, recent surgeries, or unstable cardiovascular diseases, the investigators utilized Pearson correlation and receiver operating characteristic (ROC) curve analyses to determine the primary and secondary endpoints of diagnostic cutoff values, sensitivities, and specificities.
Key Clinical Findings of the Study Includes:
Enhanced Early Detection: The investigators discovered that IOS detected abnormalities in 61.7% of asthmatic patients who had completely normal spirometry.
High-Sensitivity Reactance: The investigators found that reactance at 5 Hertz (X5) exhibited a high sensitivity of 90.5% but low specificity of 27.6% at a cutoff of −0.06 kPa/(L/s).
Optimal Resistance Thresholds: The investigators established that a resistance cutoff of 0.64 kPa/(L/s) at 5 Hertz (R5) offered 67.9% sensitivity and 59.5% specificity.
Monitoring Asthma Control: The investigators noted that pre-bronchodilator resistance at 5 Hertz was significantly higher in uncontrolled asthma at 0.9 kPa/(L/s) compared to well-controlled cases at 0.6 kPa/(L/s).
Strong Pulmonary Correlation: The investigators demonstrated that resistance at 5 Hertz negatively correlated with forced expiratory volume in 1 second (FEV1) (r = −0.49, P = 0.001), reflecting worsening obstruction.
The results suggest that IOS is an exceptionally sensitive modality for evaluating lung function, demonstrating an 84.9% concordance rate with abnormal spirometry while successfully identifying peripheral small airway dysfunction in 61.7% of patients who otherwise present with normal spirometric findings. This confirms the system's unique capability to uncover early, subtle changes in respiratory mechanics and airway resistance that conventional forced expiratory volume tests frequently overlook.
Thus, the study concludes clinicians adopting IOS as a routine complementary tool alongside conventional spirometry to enhance the early detection of small airway disease, improve monitoring of disease control, and optimize therapeutic management for asthmatic patients.
Although the cross-sectional, single-center study in Western India was limited by its sample size of 100 patients, future multi-center prospective trials with larger cohorts could help validate and refine these standardized diagnostic cutoff values across a broader, more diverse clinical population.
Reference
Malik AS, Italiya BK, Shinde R, Dugad SR. Evaluating the diagnostic utility of impulse oscillometry system versus spirometry in diagnosing bronchial asthma among adults in Western India: A diagnostic test accuracy study. Indian J Allergy Asthma Immunol 2026;40:24-31.
