Exhaled nitric oxide levels in COPD patients who use electronic cigarettes.

Emerging data from clinical studies have shown pro-inflammatory effects associated with e-cigarette use. Fractional exhaled nitric oxide (FeNO) is a biomarker of pulmonary type 2 (T2) inflammation. The effect of chronic e-cigarette use on FeNO is unclear. The aim of this study was to compare FeNO levels in COPD ex-smokers who use e-cigarettes (COPDE + e-cig) to COPDE ex-smokers (COPDE) and COPD current smokers (COPDS). FeNO levels were significantly higher in COPDE + e-cig (median 16.2 ppb) and COPDE (median 18.0 ppb) compared to COPDS (median 7.6 ppb) (p = 0.0003 and p < 0.0001 respectively). There was no difference in FeNO levels between COPDE + e-cig compared to COPDE (p > 0.9). The importance of our results is that electronic cigarette use does not alter the interpretation of FeNO results, and so does not interfere with the use of FeNO as a practical biomarker of T2 inflammation, unlike current cigarette smoking in COPD. Whilst the effect of electronic cigarette use on FeNO levels is not the same as cigarette smoke, this cannot be taken as evidence that electronic cigarettes are harmless. These differential pulmonary effects can be attributed to differences in the chemical composition of the two products.