Background: Exhaled nitric oxide (FeNO) is a non-invasive marker of airway inflammation. Smokingreduces FeNO by 30-60%. Weak positive relation between lung function and FeNO has been inconsistently described. This has not been separately for smokers. Therefore we investigated the relation between lung function and FeNO with regard to smoking.
Methods: FeNO and lung function post-bronchodilation (BD) were measured in 4813 subjects from the European Community Respiratory Health Survey III. GLI reference values were used. Smoking habits were self-reported.
Results: Current smokers with FEV1 <lower limit of normal (LLN) had lower FeNO levels (ppb, geometric mean (95%CI)) than subjects with FEV1 ≥LLN: 10.1 (9.1, 11.1) vs 11.7 (11.3, 12.2), p=0.005, while the opposite was found in non-smokers: 20.0 (18.4, 21.6) vs 18.5 (18.2, 18.8), p=0.03. This interaction with current smoking was significant both before and after adjustments for study centres, age, BMI and gender (p=0.001 and p=0.004). Current smokers with FEV1/FVC <LLN had lower FeNO than current smokers with FEV1/FVC ≥LLN: 10.5 (9.4, 11.6) vs 11.6 (11.2, 12.1), p=0.04, and the opposite was found in non-smokers: 20.8 (19.1, 22.7) vs 18.4 (18.1, 18.8), p<0.001. There was a significant interaction with current smoking both in unadjusted and adjusted models (both p<0.001).
Conclusion: Higher FeNO relates with lower FEV1 and FEV1/FVC-ratio among non-smoking individuals, suggesting that the obstruction is related with airways inflammation. In current smokers, higher FeNO relates with better preserved lung function and this finding warrants further studies to understand the underlying mechanisms. Presented on behalf of ECRHS III (www.ecrhs.org)
2018.