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 wer e 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 21-4 8, 16 male, 10 female) with normal findings in flow-volume spirometry, pulm onary diffusing capacity, relative amount of blood eosinophils, chest X-ray and ECG at rest. NOexp was determined according to the European Respirator y Society guidelines during slow expiration against an airflow resistance. The measurements were repeated after 7 (n = 13) and 23 days (n = 17). The m ean 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 mea n (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 i ntraindividual 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 va lues 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.