Age and height trajectories of exhaled nitric oxide in schoolchildren

Introduction: Exhaled nitric oxide (FeNO), produced by inducible nitric oxide synthase in airway epithelial cells, is a marker of airway inflammation used in clinical care and research. Sex, age, and height associations with FeNO during the period of somatic growth have been explained by differences in lung size. These studies are primarily based on cross-sectional data (e.g., Jacinto, T. et al. J Breath Res 2015; 9(3):036005), with little longitudinal data reported. Aims: Describe trajectories of FeNO as a function of sex, age, and height in schoolchildren. Methods: 50 ml/s FeNO was collected longitudinally in a population-based sample of 1806 southern California schoolchildren without asthma (starting at ages 7-9), with 6 visits over 8 years. Smooth sex-specific trajectories of log FeNO versus height or age were estimated using a generalized additive mixed model, with participant-level random intercepts. Results: 55% of participants had 5+ measurements of FeNO. Trajectories were different for males and females, with linear trajectories in height (Figure 1). Nonlinear trajectories in age were similar by sex until age ~11.5, after which boys had higher FeNO. Conclusions: FeNO trajectories estimated using longitudinal data provide novel evidence of sex differences after age 11 and nonlinearity prior to age 14. Future efforts will investigate joint effects of age and height.