Patterns of perinasal fluid flow and contractions of the diaphragm in the human fetus

Our aim was to identify patterns of fetal perinasal fluid flow, and to determine the relationship of pattern of flow to the diaphragmatic component of fetal breathing movements. Twenty-four fetuses were studied with the use of two ultrasound systems simultaneously. Continuous video-tape records of the color and spectral Doppler imaging of fluid flow velocity in the nose and of the movements of the fetal diaphragm were made on two video recorders during 30-min study sessions. Two different patterns of fetal perinasal flow were recognized. One type had a rapid rate and low amplitude, and was independent of ultrasonographically observed movements of the fetal diaphragm. The other type had a lower rate and higher amplitude, and was uniformly related to diaphragmatic contractions. The breath-to-breath interval, time of inspiration, time of expiration and peak inspiratory and expiratory velocities were determined for each type of perinasal flow. Two ratios were used to quantify the change of peak flow velocity. There were significant differences in the values of all timing parameters between diaphragm-related perinasal flow velocities and those not related to the diaphragm, at both 30-36 and 37-41 weeks of gestation. The rate of perinasal flow related to diaphragmatic contraction cycles was one-third that of the flow cycles not related to diaphragmatic contraction (approximately 50 vs. 148 cycles/min). For both patterns of perinasal flow velocity, the expiratory peak velocity ratio was about 1.6 times higher than the inspiratory peak velocity ratio. We conclude that, in uncomplicated pregnancy, one pattern of fetal perinasal fluid flow reflects activity of the diaphragm. We speculate that the contractions of the fetal airway smooth muscle or oropharyngeal-laryngeal muscle groups are the origin of the second pattern of perinasal flow.