Tension fetal arterial

Normal values for the various determinants of 02 transfer are necessary for quantitative analysis of the exchange process. Some values— e.g., those for the maternal and fetal arterial 02 tensions, 02 capacities, and 02 affinities—are fairly well defined. Others—e.g., the diffusing capacity and maternal and fetal placental blood flows—are less well determined. 

Effect of Varying Fetal Arterial 02 Tension. Placental exchange has usually been considered limited by either maternal and fetal blood flows or by diffusion. The present analysis suggests umbilical arterial p02 (Pf) is a third and very important factor, based on the observation... 

Figure 17 shows that end-capillary po2 is most sensitive to changes in fetal arterial 02 tension (Pf). It is less sensitive to maternal and fetal hemoglobin flow rates and the Qm/Qf ratio. Changes in maternal arterial p02 (Pm), DPf and the sum of (Qm + 0/) have little effect in the physio-... 

IV. Fetal Arterial Oxygen Tension Implications for Carotid Chemoreceptor Maturation... 

Figure 9. The effects of changes in maternal arterial 02 tension on maternal and fetal end-capillary pq2 and mean rate of Oz exchange. Moderate increases in maternal arterial p0 above normal values (95 mm Hg) increase end-capillary Poo and mean 02 exchange rate only slightly, hut decreases in maternal arterial p02 produce substantial decrease in 02 exchange and end-capillary values.

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. 

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