Low levels of exhaled nitric oxide are associated with impaired lung function in cystic fibrosis

Fraction of exhaled nitric oxide (FENO) is often reduced in cystic fibrosis (CF). FENO at different expiratory flows can provide an indication of the site of nitric oxide production. The aim of this study was to examine whether NO parameters are related to overall (FEV1) or peripheral (lung clearance index, LCI, measured by multiple breath SF6 washout) airway function and systemic inflammation in CF. Secondary aim was to compare alveolar NO and bronchial NO flux calculated by two different mathematical models, a linear and a nonlinear method. Thirty‐five healthy and 45 CF children were recruited. FENO at 50 ml/sec (FENO50) and bronchial NO flux were lower in CF than controls, 9.5 (2.7–38.8) (median (range)) versus 12.4 (5.2–40.1) ppb, P = 0.029, and 391 (97–1772) versus 578 (123–1993) (pl/sec), P = 0.036, respectively. No difference in alveolar NO was shown. The nonlinear method resulted in lower alveolar NO and higher bronchial flux, than the linear method, but the result was closely correlated in both groups. LCI was higher in CF than controls, 8.4 (6.5–12.9) versus 5.9 (5.1–7.8), P