Exhaled nitric oxide and its long-term variation in healthy non-smoking subjects

Exhaled nitric oxide (NOexp) is an indicator of inflammation in the airways. Reference values obtained from healthy adults or information on long‐term variation of NOexp are not yet available. The aims of this pilot study were to collect values of NOexp from a selected group of healthy adults and to assess their long‐term variation. We studied 26 healthy subjects (age 21–48, 16 male, 10 female) with normal findings in flow‐volume spirometry, pulmonary diffusing capacity, relative amount of blood eosinophils, chest X‐ray and ECG at rest. NOexp was determined according to the European Respiratory Society guidelines during slow expiration against an airflow resistance. The measurements were repeated after 7 (n=13) and 23 days (n=17). The mean value of NOexp (n=26) was 6·9 ng g–1 (95% confidence interval, 6·0–7·9 ng g–1). The upper limit of intra‐individual variation (+2 SD) was 11·9 ng g–1 and the lower limit (–2 SD) 1·9 ng g–1, respectively. The mean (SD) value of NO production (NO output) was 39·1 pmol s–1 (20 pmol s–1). We found no correlation between NOexp and age (r=–0·06, P=0·78) and no association of NOexp with the gender (male vs. female, P=0·40). The intraindividual coefficient of variation (CoV) was 15·8% of NOexp and 20·7% of NO output within the interval of 7 days. CoV was 16·8% of NOexp and 18% of NO output within the interval 23 days. The results suggest that NOexp values over 12 ng g–1 are abnormally high in healthy subjects. According to the results the change of NOexp by 30–35% or more within the interval of 1–3 weeks would be abnormal.