Effect of smoking on exhaled nitric oxide and flow-independent nitric oxide exchange parameters

It is a well-known fact that smoking is associated with a reduction in exhaled nitric oxide (NO) levels. There is, however, limited knowledge relating to the smoking-induced changes in production or exchange of NO in different compartments of the airways. This study comprised 221 adult subjects from the European Community Respiratory Health Survey 11, who were investigated in terms of their exhaled NO, lung function, immunoglobulin E sensitisation and smoking habits. The following parameters were determined using extended NO analysis: airway tissue nitric oxide concentration (Caw,NO), airway transfer factor (or diffusing capacity) for nitric oxide (Daw,NO), alveolar nitric oxide concentration (CA,No) and fractional exhaled nitric oxide concentration at a flow rate of 50 mL(.)s(-1) (FeNO,0.05). Maximum total airway nitric oxide flux (J'aw,NO) was calculated from Daw,NO(Caw,NO-CA,NO). Current smokers (n=35) exhibited lower (geometric mean) FeNO,0.05 (14.0 versus 22.8 ppb), Caw,NO (79.0 versus 126 ppb) and J'aw,NO (688 versus 1,153 pL(.)s(-1)) than never-smokers (n=111). Ex-smokers (n=75) were characterised by lower FeNO,0.05 (17.7 versus 22.8 ppb) and Jaw,NO (858 versus 1,153 pL-s(-1)) than never-smokers. These relationships were maintained after adjusting for potential confounders (sex, age, height, immunoglobulin E sensitisation and forced expiratory volume in one second), and, in this analysis, a negative association was found between current smoking and CA,NO. Snus (oral moist snuff) consumption (n=21) in ex-smokers was associated with an increase in Daw,NO and a reduction in Caw,No, after adjusting for potential confounders. Passive smoking was associated with a higher CA,NO. Using extended nitric oxide analysis, it was possible to attribute the reduction in exhaled nitric oxide levels seen in ex- and current smokers to 6 lower total airway nitric oxide flux in ex-smokers and reduced airway and alveolar nitric oxide concentrations in current smokers. The association between snus (oral tobacco) use and reduced nitric oxide concentrations in the airways and increased nitric oxide transfer from the airways warrants further studies.