Measurements of upper and lower airway nitric oxide in healthy adults.

Introduction.Nasal nitric oxide (NO) measurement can be a useful tool for monitoring upper airway diseases. However, there is a considerable lack of validation data.Aims.To evaluate the repeatability and intra-subject variations of nasal NO output (nVNO) in healthy adults and to study its correlation with lower airway NO parameters.Methods.nVNOwas measured in healthy non-smokers at baseline (N= 31, age: 28 ± 6 years), after 1 h (N= 15), 1 d (N= 15), 1 week (N= 17), and compared using the Bland-Altman method. At baseline, lower airway NO parameters (FENO, flux of NO in the conducting airways and alveolar NO concentration) were also measured and correlated tonVNO(Spearman correlation). Multivariate regression analysis was used to assess the factors influencingnVNO.Results.Baseline mediannVNOwas 465 (interquartile range (IQR) = 404-536) nL min-1. The mean differences between the baseline and repeated measurements were not significant (p> 0.05). The coefficient of repeatability (mean: 118, IQR = 88-181 nL min-1) and coefficient of variation (mean: 9.1%) were low. We found no correlation betweennVNOand lower airway NO parameters (p> 0.05). Sex (β= -0.52,p= 0.02) and body weight (β= -0.65,p= 0.03) influencednVNO(model:p= 0.04,R2= 0.31).Conclusion.nasal NO output has good repeatability in healthy adults. The NO productions of lower and upper airways are not related in health, but nasal NO output seems to be affected by sex and body weight.