Intra-breath measures of respiratory mechanics in healthy African infants detect risk of respiratory illness in early life

Rationale: Lower respiratory tract illness (LRTI) is a leading cause of mortality and morbidity in children. Sensitive and non-invasive infant lung function techniques are needed to measure risk for and impact of LRTI on lung health. Objective: To investigate whether lung function derived from the intra-breath forced oscillation technique (FOT), was able to identify healthy infants at risk of LRTI in the first year. Methods and Measurements: Lung function was measured with the novel intra-breath FOT, in six-week infants in a South African birth cohort (Drakenstein Child Health Study). LRTI during the first year was confirmed by study staff. The association between baseline lung function and LRTI was assessed with logistic regression and odds ratios (ORs) determined using optimal cut-off values. Results: Of the 627 healthy infants with successful lung function testing, 161(24%) had 238 LRTI episodes subsequently during the first year. Volume dependence of respiratory resistance (ΔR) and reactance (ΔX) were associated with LRTI. The predictive value was stronger if LRTI was recurrent (n=50, 31%): OR=2.5, ΔX; required hospitalisation (n=38, 16%): OR=5.4, ΔR; or was associated with wheeze (n=87, 37%): OR=3.9, ΔX. Conclusion: Intra-breath FOT can identify healthy infants at risk of developing LRTI, wheezing or severe illness in the first year of life.