Tension umbilical arterial

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... 

Changes in umbilical arterial po2 will alter both end-capillary 02 tension and 02 transfer rate (Figure 10), but these two responses occur in opposite directions and offset one another to maintain 02 transfer... 

It was recently proposed that kinin is responsible for the circulatory changes at birth which result in conversion of the foetal to the new-born circulation. Presumably, the decreased temperature of the umbilical cord, the increased partial tension of oxygen in the blood and the increased concentration of circulating granulocytes all activate the kininogenase and thus induce kinin release. Kinin then constricts the umbilical artery and vein and the ductus arteriosus and dilates the pulmonary vasculature. All these effects of kinin have been confirmed experimentally in the lamb. 

We have tried to circumvent these problems by isolating a cotyledon of the placenta and perfusing its umbilical circulation in situ with blood of known and accurately controlled flow rates and 02 tensions (47). We have also varied maternal arterial Oo tension by administering various concentrations of inspired 02. 

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