Circulatory responses to maternal hyperoxaemia and hypoxaemia assessed non‐invasively in fetal sheep at 0.3–0.5 gestation in acute experiments

Abstract

Maternal hypoxaemia in early pregnancy causes similar fetal circulatory responses to those in late pregnancy: bradycardia, reduced venous flow velocities, augmented pulsatility in veins and a redistributional flow velocity pattern of the umbilical and common carotid arteries.

Ductus venosus velocimetry in acute fetal acidemia and impending fetal death in a sheep model of increased placental vascular resistance

“…Our finding is in agreement with published experimental studies (13,22). It has been shown that a comparable degree of fetal hypoxemia with our study caused a profound and immediate distension of the DV inlet (14,22).…”

“…Hypoxemia leads to the dilatation of DV and an increase in the volume blood flow shunting through it (14,20). Studies on fetal sheep in early pregnancy have shown increased pulsatility in DV blood velocity waveform pattern during hypoxemia (13). Another mechanistic pathway leading to increased pulsatility in Doppler-derived DV blood velocity waveform can be a rise in end-diastolic pressure of the ventricles (11).…”

The human ductus venosus between 13 and 17 weeks of gestation: histological and morphometric studies

“…The novel finding, on scanning electron microscopy, of longitudinal corrugations on the endothelial surface of the ductus venosus may have functional relevance. The hourglass shape, endothelial corrugations and the elastin-rich adventitia may assist in the process of dilatation of the ductus venosus 1,2 .…”

“…Recently, animal studies have demonstrated that the ductus venosus diameter increases in response to fetal hypoxemia, enhancing the shunting of oxygenated blood 1,2 . There is, however, conflicting evidence from previous studies about the structure of the ductus venosus, especially with regard to the presence of a sphincter at the ductus venosus inlet [9][10][11][12][13][14][15][16][17] .…”

“…These shunts ensure that highly oxygenated blood from the placenta is delivered to the fetal brain and heart, bypassing the fetal hepatic and pulmonary circulations. It has been proposed that shunting of umbilical blood through the ductus venosus is actively regulated at the level of the ductus venosus inlet, and that the degree of shunting varies under different physiological and pathological conditions [1][2][3][4][5][6][7][8] .…”