Relationships among Doppler-derived umbilical artery absolute velocities, cardiac function, and placental volume blood flow and resistance in fetal sheep

Abstract

We hypothesized that umbilical artery (UA) absolute blood flow velocities measured by Doppler ultrasonography reflect placental volume blood flow (Q(UA)) and placental vascular resistance (R(UA)) in a late gestation fetal sheep model. In addition, we examined the relationships between umbilical artery absolute blood flow velocities and parameters of fetal cardiac function. Twenty-six sheep fetuses were instrumented at 112-132 days of gestation. After a 5-day recovery period, experiments were performed under general anesthesia in 16 normal fetuses, in 5 fetuses after maternal administration of phenylephrine, and in 5 fetuses after placental embolization. The Q(UA) and arterial blood pressures were measured using a transit-time ultrasonic flow probe and a catheter placed into the descending aorta, respectively. UA peak systolic velocity (PSV), end-diastolic velocity (EDV), time-averaged maximum velocity (TAMXV), pulsatility index (PI), mean velocity (V(mean)), fetal cardiac output, ventricular ejection forces, and the proportion of isovolumetric relaxation time (IRT%) in the cardiac cycle were measured with the use of Doppler ultrasonography. Significant positive linear correlations were found between UA EDV, TAMXV, and V(mean) versus Q(UA), whereas UA PI had a significant negative correlation with Q(UA). Significant negative correlations were shown between UA EDV, TAMXV, and V(mean) versus R(UA). A significant positive correlation was present between UA PI and R(UA). Doppler-derived UA parameters did not correlate with fetal arterial blood pressures, cardiac output, ventricular ejection forces or IRT%. In fetal sheep, Doppler-derived UA PI and absolute velocities, except PSV, are closely related to directly measured Q(UA) and R(UA), validating the use of noninvasive Doppler velocimetry in the assessment of placental circulation.

Laparoscopy Guided Doppler Ultrasound Measurement of Fetal Blood Flow Indices During Early to Mid-Gestation in Pigs

“…The systolic peak and time averaged velocities did not change during the examined gestational period. In porcine fetuses, the PSV was two-times higher compared with that of rabbits [37] but half that of sheep fetuses [38]. Apparently, differences exist concerning species, the number of fetuses and the stage of gestation.…”

“…In porcine fetuses, the PSV was two-times higher compared with that of rabbits [37] but half that of sheep fetuses [38]. Apparently, differences exist concerning species, the number of fetuses and the stage of gestation.Volumetric blood flow assessment in small, convoluted umbilical arteries is difficult [38]. Therefore, qualitative analysis of blood flow velocity waveforms [16] or semiquantitative indexes, such as RI and PI, are often used.…”

Comparison of foetal growth in singleton and twin pregnancies byB-mode and Doppler ultrasonography in Karya ewes

“…The use of ultrasonography minimises the slaughter rate of pregnant animals, facilitates optimal feeding for ideal birth weight, and reduces feed cost in females carrying a singleton (1)(2)(3)(4). Moreover, the pregnant ewe model being used in numerous human biomedical studies and ultrasound examination of foetuses in the intrauterine environment emphasises the multidisciplinary importance of this method (5,6).…”

Mechanism of Acute Fetal Cardiovascular Depression after Maternal Inflammatory Challenge in Mouse

“…A significant correlation exists between umbilical artery PI values and placental vascular resistance. 30 Because a substantial proportion of the descending aorta volume blood flow is directed to placenta, the increase in placental vascular resistance is also reflected in the descending aorta vascular impedance. Thus, the results indicate an acute increase in the placental vascular resistance and fetal cardiac afterload.…”