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 10 min 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 (postconceptional 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.