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

Introduction Nasal nitric oxide (nNO) 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 nNO output (nVNO) in healthy adults and to study its correlation with lower airway NO parameters. Methods nVNO was measured in healthy non-smokers at baseline (N=31, age: 28±6 years), after 1 hour (N=15), 1 day (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 to nVNO (Spearman correlation). Multivariate regression analysis was used to assess the factors influencing nVNO. Results Baseline median nVNO was 465 (interquartile range=404-536) nL/min. The mean differences between the baseline and repeated measurements were not significant (p>0.05). The coefficient of repeatability (mean: 118, interquartile range=88-181 nL/min) and coefficient of variation (mean: 9.1%) were low. We found no correlation between nVNO and lower airway NO parameters (p>0.05). Sex (β=-0.52, p=0.02) and body weight (β=-0.65, p=0.03) influenced nVNO (model: p=0.04, R2=0.31). Conclusion nNO 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.