Exhaled breath condensate pH and exhaled nitric oxide in allergic asthma and in cystic fibrosis

Background: It has been proposed that the pH of airway lining fluid may regulate the fractional exhaled concentration of nitric oxide (Fe_NO) in respiratory disease. Methods: Fe_NO, exhaled breath condensate (EBC) pH, and EBC concentrations of nitrite plus nitrate (NO₂/NO₃) were compared in 12 subjects with stable asthma, 18 with stable cystic fibrosis (CF), and 15 healthy control subjects. Eight of the CF patients were studied on a separate occasion at the start of a pulmonary exacerbation. Results: Fe_NO was significantly greater in asthmatic subjects than in control subjects (mean 35 v 9 ppb, p<0.001). EBC pH, however, was similar in the asthmatic and control groups (median 5.82 v 6.08, p = 0.23). Levels of NO₂/NO₃ were on average higher in EBC samples from asthmatic subjects, but the difference was not significant. In patients with stable CF both the Fe_NO (mean 4 ppb, p<0.001) and EBC pH (median 5.77, p = 0.003) were lower than in the control group. Levels of EBC NO₂/NO₃ (median 29.9 μM; p = 0.002) in patients with stable CF, in contrast, were significantly higher than in control subjects. During CF exacerbations, EBC pH was further reduced (median 5.30, p = 0.017) but Fe_NO and NO₂/NO₃ were unchanged. Conclusions: These findings demonstrate a dissociation between EBC pH and Fe_NO in inflammatory airways disease.