Introduction: We previously reported the use of blood oxygen level dependant functional MRI (BOLD-fMRI) for monitoring hemodynamic changes in placenta and fetal organs in mice. Here we describe the use of BOLD-fMRI to compare ephedrine and phenylephrine for effects on placental and fetal organ perfusion.

Methods: Pregnant ICR mice (n=16; E17.5) were anesthetized with pentobarbital (30mg/kg i.p.) and placed supine in a 4.7-T Bruker Biospec MRI spectrometer. Following baseline images, ephedrine (1mg/kg) or phenylephrine (1 mcg/kg) were administered intravenously. Equipotential doses were selected from a pilot study in anesthetized pregnant Wistar rats with femoral artery pressure transduction. Changes in placental and fetal perfusion following ephedrine or phenylephrine administration were analyzed from T2*-weighted gradient echo MR images (TR/TE=147/10 ms). Different regions of interest (placenta, fetal heart, fetal liver and fetal brain) were identified on True-FISP images using home written IDL software. Percentage change of MR signal intensity (%ΔSI) following the administration of equipotential doses of either ephedrine or phenylephrine were calculated and presented by time curves.

Results : We observed that the effects of ephedrine and phenylephrine were markedly different. Phenylephrine caused a marked reduction in placental and fetal heart and fetal liver signal intensity, but fetal brain SI was unchanged. The time course of fetal cerebral perfusion following phenylephrine (Fig 1) was statistically different from that of the placenta and all other fetal organs (p<0.001). Additionally, the fetal brain: fetal liver %ΔSI ratio was markedly increased with respect to baseline (p<0.001). The time course of fetal cerebral perfusion following ephedrine (Fig 2) was only statistically different from that of the fetal heart (p<0.001). Fetal heart SI was markedly reduced with respect to baseline (p<0.001).

Discussion : Ephedrine increased maternal liver and placental SI and decreased fetal heart SI; this was apparently related to increased maternal cardiac output with increased fetal myocardial oxygen demand. Phenylephrine markedly reduced placental and fetal organ SI, except for fetal brain SI which was minimally changed; this was apparently indicative of acute placental and fetal asphyxia with fetal brain sparing. BOLD fMRI has potential as a tool for non-invasive hemodynamic and pharmacodynamic monitoring of the placental and fetal circulation.

Authors:

Y. Ginosar, J. Shapiro, N. Corchia, U. Elchalal, R. Abramovich

Hadassah Hebrew University Medical Center, Jerusalem, Israel