Abstract 62

Background/Aim: Endogenous NO in the exhaled gas has an important role in lung physiology (e.g. VQ matching, inflammation).

Methods: We studied tidal vari-ations of NO exhaled from the respiratory tract of 24 newborns (n = 15 and 9 premature and term infants, respectively) during spontaneous nasal breathing on day 9 ± 13 (mean ± SD) postnatally. Gas was sampled at 0.19 L min-1 via a thin nasal catheter placed in the hypopharynx in the absence of acute respiratory compromise. NO was measured by fast response ultra-sensitive chemilumi-nescence analysis and assigned to the upper or lower respiratory tract using synchronized tidal CO2 analysis.

Results: Lower airway NO was 1.9 ± 0.9 ppb and not significantly correlated with weight, gestatio-nal or postnatal age. Autoinhaled nasal NO peaks during regular breathing were 12.0 ± 8.3 ppb and reached maxima of 50.9 ± 28.5 ppb after breathholds. During regular breathing 7 infants exhi-bited sudden decreases to periods of nasal NO peaks with < 50% ampli-tude suggesting transient shortage of autoinhaled nasal NO.

Conclusion: NO exhaled from the lower respiratory tract can non-invasively be distinguished from nasally derived NO during sponta-neous breathing in the newborn.

Supported by DFG AR 205/2-1.