Preschool Oscillometry and Later Asthma-Related Outcomes: A Systematic Review of Longitudinal Studies

Background: Preschool wheezing is common, but distinguishing transient wheezing from early persistent asthma remains difficult. Oscillometric techniques, including impulse oscillometry (IOS), may provide objective prognostic information. Objective: To systematically review longitudinal studies assessing whether oscillometric measurements obtained at preschool age are associated with later asthma-related outcomes or lung function impairment. Methods: PubMed, Scopus, and MEDLINE (via EBSCOhost) were searched from inception to 28 February 2026. Eligible studies included preschool-aged children or closely related early-childhood populations assessed with IOS or forced oscillation technique (FOT), longitudinal follow-up, and later asthma-related or spirometric outcomes. Two reviewers independently screened studies, extracted data, and assessed risk of bias with QUIPS. Owing to substantial heterogeneity, findings were synthesized qualitatively. Results: Seven longitudinal cohort studies, encompassing 1077 children, met the eligibility criteria; baseline oscillometry was performed between ages 2 and 7 years, and follow-up ranged from 1 to 10 years. Short-term classification and longer-term prognostic studies were interpreted separately. Resistance-based indices, particularly R5, showed the most consistent associations with later asthma-related outcomes and lower subsequent spirometric indices, including FEV₁ and FEV_1/FVC. Most studies were at moderate risk of bias, and some reports came from related cohorts. Conclusions: Preschool oscillometry may provide complementary physiological information to assess asthma risk in symptomatic or high-risk preschool-aged children, particularly through resistance-based measures. However, evidence remains limited, heterogeneous, and insufficient to support a single validated cutoff, routine screening of apparently healthy children, or routine stand-alone prognostic use.