F48Vasoconstrictor effect of the proximal segment of the fetal middle cerebral artery after an external partial occlusion of the umbilical vein (vasoconstrictor reflex)

Abstract

BackgroundWe studied the repercussion of the nuchal cords on the proximal segment of the middle cerebral artery (pMCA) (segment with a rich innervation).MethodWe performed an external partial occlusion of the umbilical vein (through maternal abdominal wall) during 1–2 s to stimulate the baroreflex (pressure test or PT). We performed 76 PT in 36 fetuses. The pMCA was studied sonographically before, during and after the PT through pulsed Doppler and color Doppler energy (CDE).ResultsDuring the PT we observed stop the whole of the umbilical vein flow while maintaining the flow of the umbilical arteries. We observe a vasoconstrictor effect on the pMCA using CDE. This effect reflected a moderate‐severe segmental stenosis in the pMCA, however, flow in the remaining MCA was maintained. Sometimes, the effect vasoconstrictor produced a reverse flow on the pMCA to pulsed Doppler study. Post occlusion a cerebral vasodilatation took place, although in occasions an increased vascular tone persisted. Some fetal movements also could produce a similar effect in the pMCA (spontaneous PT).ConclusionThe PT produces an effect vasoconstrictor in the pMCA. Variations of this reflex can be the origin of some perinatal motor injury of intrauterine origin.