PATTERNS OF PERINASAL FLUID-FLOW AND CONTRACTIONS OF THE DIAPHRAGM INTHE 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 co mponent of fetal breathing movements. Twenty-four fetuses were studied with the use of two ultrasound systems simultaneously. Continuous vid eotape 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 differe nt patterns of fetal perinasal flow were recognized. One type had a ra pid rate and low amplitude, and was independent of ultrasonographicall y observed movements of the fetal diaphragm. The other type had a lowe r rate and higher amplitude, and was uniformly related to diaphragmati c contractions. The breath-to-breath interval, time of inspiration, ti me of expiration and peak inspiratory and expiratory velocities were d etermined for each type of perinasal pow Two ratios were used to quant ify the change of peak flow velocity. There were significant differenc es in the values of all timing parameters between diaphragm-related pe rinasal flow velocities and those not related to the diaphragm, at bot h 30-36 and 37-41 weeks of gestation. The rate of perinasal flow relat ed 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 exp iratory peak velocity ratio was about 1.6 times higher than the inspir atory peak velocity ratio. We conclude that, in uncomplicated pregnanc y, one pattern of fetal perinasal fluid flow reflects activity of the diaphragm. We speculate that the contractions of the fetal airway smoo th muscle or oropharyngeal-laryngeal muscle groups are the origin of t he second pattern of perinasal flow.