Endogenous nitric oxide in the upper airways of premature and term infants

Concentrations of endogenous nitric oxide (NO) were measured in premature ( n = 18) and term infants ( n = 7). Nasal gas was aspirated continuously and after timed occlusions, 15 s and 60 s, by a fast-response chemiluminescence analyser. The sampling flow rate was 20 ml min^-1. Typical NO recordings consisted of plateaux and postocclusive peaks. In term infants peak NO concentrations (60 s occlusion) were 2. 71 ± 0. 44 parts per million (ppm) within lOmin after birth, increasing ( p < 0. 05) to 3. 81 ± 0. 25 ppm at 4–7 d postnatally. Peak NO values (15 s occlusion) averaged 1. 22 ± 0. 16 ppm in premature infants (postconcep-tional age 25–37 weeks, body weight 623–2844 g) and the NO concentrations increased significantly with postconceptional age ( p < 0. 05). Nasal excretion rate, estimated from plateau NO concentrations and sampling flow rate, was 0. 10 ± 0. 01 nmol min^-1 kg^-1 in both groups. We conclude that premature and term newborn infants excrete considerable amounts of NO in the upper airways, with hitherto not fully known functions.