Correlation between impulse oscillometry and spirometry parameters in Indian patients with cystic fibrosis

Impulse oscillometry (IOS) is an emerging tool to assess lung function in chronic respiratory diseases, more often in preschool children and patients who are unable to perform spirometry. We conducted a prospective cross-sectional study on patients with cystic fibrosis (CF). Primary objective was to evaluate correlation between IOS and spirometry parameters. Secondary objective was to evaluate the ability of IOS parameters to discriminate patients with airflow limitation at various forced expiratory volume in 1 second (FEV₁) cutoffs. Patients with CF above 6 years of age, who were following up on a routine visit, were enrolled in the study. Patients underwent IOS and spirometry as per guidelines. A total of 39 patients (34 children and 5 adults) were enrolled in the study. There was a significant moderate negative correlation between spirometry parameters (FEV₁, forced vital capacity, and peak expiratory flow rate) and IOS parameters, that is, impedance at 5 Hz (Z5), resistance at 5 Hz (R5), and reactance area, both between raw values and percent predicted values. Of the various IOS parameters, Z5 percent predicted had the maximum area under the curve (AUC) of 0.8152 and 0.8448 for identifying children with FEV₁ <60% and <80%, respectively. R5 percent predicted had an AUC of 0.8185 for identifying children with FEV₁ <40%. IOS can be used as an alternative pulmonary function test in patients with CF more so in patients who are unable to perform spirometry.