Impulse oscillometry at preschool age is a strong predictor of lung function by flow‐volume spirometry in adolescence

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Background The transition from early childhood wheezing to persistent asthma is linked to lung function impairment over time. Little is known how the methods used to study lung function at different ages correlate longitudinally. Methods Sixty‐four children with a history of hospitalization for bronchiolitis before 6 months of age were prospectively studied with impulse oscillometry (IOS) at the mean age of 6.3 years and these preschool IOS results were compared with flow‐volume spirometry (FVS) measurements at mean age of 11.4 years. Results The baseline respiratory system resistance at 5 Hz (Rrs5) showed a modest statistically significant correlation with all baseline FVS parameters except FVC. The post‐bronchodilator (post‐BD) Rrs5 showed a modest statistically significant correlation with post‐BD FEV 1 and FEV 1 /FVC. The bronchodilator‐induced decrease in Rrs5 showed a modest statistically significant correlation with the percent increase in FEV 1 . Baseline and post‐BD respiratory reactance at 5 Hz (Xrs5) showed a modest statistically significant correlation with baseline and post‐BD FVS parameters except post‐BD FEV 1 /FVC, respectively, and post‐BD Xrs5 showed a strong correlation with post‐BD FVC ( ρ = 0.61) and post‐BD FEV 1 ( ρ = 0.59). In adjusted linear regression, preschool Xrs5 remained as a statistically significant independent predictor of FVS parameters in adolescence; the one‐unit decrease in the Z ‐score of preschool post‐BD Xrs5 predicted 9.6% lower post‐BD FEV 1 , 9.3% lower post‐BD FVC, and 9.7% lower post‐BD MEF 50 when expressed as %‐predicted parameters. Conclusion Persistent post‐BD small airway impairment in children with a history of bronchiolitis detected with IOS at preschool age predicted FVS results measured in early adolescence.