RESPIRATORY PHYSIOLOGY

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

J C Ojoo, S A Mulrennan, J A Kastelik, A H Morice and A E Redington

Division of Academic Medicine, Postgraduate Medical Institute, University of Hull, Hull, UK

Correspondence to:
Correspondence to:
Dr A E Redington
Respiratory Medicine, Hammersmith Hospital, Du Cane Road, London W12 0HS; a.e.redington{at}hhnt.org

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.

Abbreviations: CF, cystic fibrosis; EBC, exhaled breath condensate; FE_NO, fractional exhaled concentration of nitric oxide; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; NO, nitric oxide; PD₂₀, provocative dose of methacholine required to produce a 20% fall in FEV₁

Keywords: asthma; cystic fibrosis; exhaled breath condensate; nitric oxide

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