Reduction of fractional exhaled nitric oxide (FENO) and its variation by mouth wash.

Although fractional exhaled nitric oxide (FENO) measurement is a widely used method to assess eosinophilic bronchial inflammation, knowledge on extrabronchial factors affecting measurement results is still limited. Our aim was to study the eventual modifying effect of mouth wash on FENO values and their variability. A total of 16 healthy Caucasian women performed FENO measurements with a chemiluminescence analyzer according to ATS guidelines (2005), with an exhalation flow rate of 50 ml/s against a flow resistor. On the first day three successive FENO measurements were performed: first after mouth wash with water containing sodium and potassium bicarbonates, and thereafter twice without mouth wash. On the second day, the FENO measurement was first performed without mouth wash, then with preceding mouth wash twice, and finally without preceding mouth wash. Each FENO measurement consisted of three measurements with the average reported and the time interval between the FENO measurements was 10 minutes on both days. The FENO level increased significantly in the subsequent measurements performed without mouth wash (p < 0.01), when the baseline measurement was performed with mouth wash. On the second day, the FENO level decreased significantly in measurements performed with preceding mouth wash, compared with the first measurement without preceding mouth wash (p < 0.01). The results indicate a slight but statistically significant decreasing effect of mouth wash on the FENO. The findings suggest that mouth wash prior to FENO measurement could standardize the measurement procedure, by decreasing the effect of NO produced in the mouth on the measurement result.