Increased exhaled nitric oxide on days with high outdoor air pollution is of endogenous origin

The aim of this study was to assess the effect of outdoor air pollution on exhaled levels of endogenously released nitric oxide. To exclude bias from exogenous NO in the recovered exhaled air (residual NO or NO in dead volume) an experimental design was used that sampled NO of e ndogenous origin only. The validity of the presented experimental design wa s established in experiments where subjects were exposed to high levels of exogenous NO (cigarette smoke or 480 mu g.m(-3) synthetic NO). Subsequent 1 min breathing and a final inhalation of NO-free air proved to be sufficien t to attain pre-exposure values, Using the presented method detecting only endogenous NO in exhaled air, 18 subjects were sampled on 4 seperate days with different levels of outdoor a ir pollution (read as an ambient NO level of 4, 30, 138 and 236 mu g.m(-3)) . On the 2 days with highest outdoor air pollution, exhaled NO was signific antly (p<0.001) increased (67-78%) above the mean baseline value assessed o n 4 days with virtually no outdoor air pollution, In conclusion, the level of endogenous nitric oxide in exhaled air is incre ased on days with high outdoor air pollution. The physiological implication s of this findings need to be investigated further.