Abstract
Fractional exhaled nitric oxide (F (ENO(50)) ), a marker of allergic airway inflammation, is used in respiratory research and asthma clinical care; however, its trajectory with increasing age during childhood has not been well characterised. We examined F (ENO(50)) longitudinally during a period of important somatic growth to describe trajectories across childhood and adolescence in healthy participants and evaluate clinical factors as potential determinants of trajectories.F (ENO(50)) was collected at six visits over 8 years in a population-based cohort of 1791 schoolchildren without asthma (median age at entry 8.4 years). Smooth sex-specific F (ENO(50)) trajectories were estimated using generalised additive mixed models, with participant-level random effects. We evaluated whether sex-specific trajectories were influenced by race/ethnicity, body mass index (BMI) percentile, allergic rhinitis or puberty.Different F (ENO(50)) patterns were observed by sex in later childhood and several factors were associated with either F (ENO(50)) level or change in F (ENO(50)) as participants aged. F (ENO(50)) -age trajectories were similar by sex until age ∼11.5 years, after which males had greater F (ENO(50)) change than females. This divergence in F (ENO(50)) -age trajectories coincides with puberty. Males with higher starting BMI percentile had attenuated F (ENO(50)) -age slopes. Among males, F (ENO(50)) levels were lower in non-Hispanic white subjects. Among both sexes, participants with rhinitis had higher F (ENO(50)) F (ENO(50)) levels within individuals tracked over time; however, there was considerable variation in F (ENO(50)) patterns across participants.F (ENO(50)) trajectories from longitudinal data provide evidence of sex differences coinciding with puberty, suggesting potential hormone link. Improved understanding of determinants of F (ENO(50)) trajectories is needed to realise the potential for using individualised predicted F (ENO(50)) trajectories.