Doppler assessment of tracheal and nasal fluid flow during fetal breathing movements: preliminary observations.

Our aim was to determine if it was technically possible to assess fetal tracheal fluid flow during fetal breathing movements, and to compare the data obtained with those recorded in the fetal nasopharynx. Tracheal and nasal fluid flow was analyzed in ten uncomplicated pregnancies, the gestational age ranging between 28 and 38 weeks. Color Doppler was used to detect the fluid displacement in the trachea generated by fetal breathing movements. Spectral Doppler was then used to analyze the fluid flow velocity waveforms. During the same breathing episode, nasal fluid flow was assessed by the same technique. The inspiration and expiration times were variable and not statistically comparable for both nasal and tracheal flow. Peak velocities of inspired and expired fluid were higher in the trachea than in the nose (p < 0.05). We found that the peak velocity of tracheal flow waveforms was significantly higher for inspiration than expiration (p < 0.05). No significant differences were found in the time velocity integral between inspiration and expiration (p = 0.79). The calculated intratracheal flow volume displaced during one breathing cycle increased from 1.3 to 5.0 ml with advancing gestation. Assessment of nasal and tracheal flow, using color and spectral Doppler, is feasible in the human fetus. Intratracheal flow measurements may provide an insight into the effect of fetal breathing movements on lung fluid in the human fetus.