Oxygen maternal arterial

Effects of Varying Maternal Arterial Oxygen Tension. Oxygen, air, and various N2-air mixtures were administered randomly to four ewes for 3-10-min intervals (47). The inspired gases achieved maternal arterial 02 tensions ranging from 30-350 mm Hg. During this interval the isolated... 

Figure 9 shows the effects of decreasing the oxygen capacity of maternal blood on the maternal axial oxygen partial pressure profile. In the normal case (N2 — 16 ml oxygen/100 ml blood) maternal arterial blood enters the exchange unit at an oxygen partial pressure of 90.5 mm... 

The fetal and maternal flow rates were set at 40-80 ml/min and 450 ml/min, respectively, and an amniotic fluid pressure of 15 mm Hg was maintained over the placenta throughout the experiment. Oxygen tensions were 60-160 mm Hg in the maternal artery and 14-28 mm Hg in the fetal vein. Glucose was added at the beginning of the perfusion to help maintain placental viability. 

Two umbilical arteries from the foetus carry blood to the placenta and a single umbilical vein returns blood from the placenta back to the foetus. The functions of the placenta in pregnancy are to supply oxygen and nutrients from the maternal circulation to the foetus and to remove waste materials, such as urea and carbon dioxide, from foetal blood. 

In the placenta a volume of oxygen sufficient for fetal needs must diffuse across the membranes from maternal to fetal blood during the short time the two circulations are in close contact. This oxygen transfer is a function of several factors which include uterine and umbilical arterial 02 partial pressures, maternal and fetal placental blood flow rates, the 02 capacity and 02 affinity of maternal and fetal hemoglobin, the diffusing capacity of the placenta, the amount of C02 exchanged, and the vascular arrangement of maternal to fetal vessels. 

After it was determined that changing the linear velocity of the maternal or fetal blood stream did not affect the equilibration pressure, it was possible to determine the maternal to fetal volumetric flow rate ratio that would result in an equilibration pressure which matched experimentally determined values of umbilical vein and artery oxygen partial pressures (37). As the maternal to fetal volumetric flow rate ratio is increased, the partial pressure of oxygen at which equilibration... 

Figures 17 and 18 shows the effects produced on maternal and fetal blood when the arterial oxygen partial pressure of maternal blood is decreased.

Fig. P-66. The growing fetus depends on its mother for nutrients and removal of wastes. The mother s heart pumps blood through the uterine arteries into the placenta nutrients and oxygen diffuse through the placental membranes into the fetal bloodstream by way of the umbilical cord and wastes pass in the reverse direction to the maternal bloodstream through the uterine veins.

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