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 microM; 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.