Normative values for exhaled breath condensate pH and its relationship to exhaled nitric oxide in healthy African Americans

Background: Exhaled breath condensate (EBC) pH and exhaled nitric oxide (FeNO) have been proposed as markers of asthma severity. EBC pH values below 6.5 have been associated with asthma exacerbations. Protonation of airway nitrite occurs at low pH and may contribute to FeNO. Objective: To establish normative EBC pH values and to determine the contribution of EBC pH to FeNO in healthy African Americans. Methods: Two hundred seventy healthy African American subjects without asthma between 18 and 40 years old were evaluated. Subjects had simultaneous measurement of EBC pH, EBC nitrite, nitrate, and FeNO. Results: The median EBC pH was 8.14 (interquartile range, 7.83-8.28). Of subjects, 11.9 % had an EBC pH <= 6.5. In subjects with EBC pH values below 6.5, there was an inverse correlation between EBC pH and FeNO (r(2) = 0.158; P =.0245; n = 32). In the entire cohort, there was a direct correlation between EBC pH and EBC nitrite (r(2) = 0.163; P <.0001), but there was no correlation between EBC nitrite and FeNO. In multivariate analyses, EBC pH and nitrite did not contribute significantly to FeNO variation while controlling for other confounders of FeNO. Conclusion: There was an increased prevalence (11.9%) of low EBC pH (less than 6.5) in healthy African American subjects compared with white subjects (<5%). EBC pH and nitrite were directly correlated, but there was no correlation between EBC nitrite and FeNO. FeNO correlated with EBC pH at pH values less than 6.5 in univariate but not multivariate analyses. This suggests that EBC pH and nitrite are not significant determinants of FeNO in healthy subjects.