REDUCED UPPER AIRWAY NITRIC-OXIDE IN CYSTIC-FIBROSIS

Nitric oxide (NO) produced within the respiratory tract is detectable in exhaled and nasal air. Its synthesis may be induced by inflammatory cytokines and reduced by glucocorticoids. Increased concentrations ha ve been found in asthma and bronchiectasis. In this study, NO concentr ations were determined in 63 children with cystic fibrosis, of whom 13 were on inhaled steroids (mean age 13.3 years) and 50 were not (mean age 12.3 years); 57 normal children (mean age 12.2 years) were also st udied. NO was measured by chemiluminescence analyser, exhaled NO follo wing a relaxed vital capacity manoeuvre, and nasal NO with the breath held following a full inspiration. Mean concentration of exhaled NO in cystic fibrosis patients (no steroids) was 4.7 parts per billion (ppb ) (95% confidence interval (CI) 4.0 to 5.3); this did not differ from values in normal children (mean 4.8 ppb, 95% CI 3.8 to 5.8) or in cyst ic fibrosis patients on inhaled steroids (mean 3.6 ppb, 95% CI 2.5 to 4.8). Nasal concentrations were significantly lower in cystic fibrosis patients, with or without inhaled steroids, than in normal children ( cystic fibrosis, no inhaled steroids: 460 ppb, 95% CI 399 to 520; cyst ic fibrosis, inhaled steroids: 522 ppb, 95% CI 313 to 730, v normal ch ildren: 1024 ppb, 95% CI 896 to 1152, p<0.0001). Considering the infla mmatory nature of cystic fibrosis, it is surprising exhaled NO levels were not increased, but this may have been due to alteration in NO dif fusion through thick mucus. The low nasal NO concentrations, which are probably the result of impaired flow from the paranasal sinuses, may contribute to the recurrent respiratory infections typical of cystic f ibrosis.