Acute embolization of the uteroplacental circulation: uterine blood flow and placental CO diffusing capacity.
In an effort to determine to what extent the fetal sequalae following repeated embolization result from decreased area of placental exchange or from decreased uterine blood flow, we injected microspheres into the uterine circulation of the pregnant ewe. We measured total UBF continuously and sampled fetal blood gases in 6 chronically instrumented ewes following repeated injections of 1 to 2 million 25 mu microspheres into the common internal iliac artery at 30 min intervals. Embolization resulted in an immediate 25 to 30% drop in uterine flow, with partial recovery to about 85% of its control value within 30 min after injection. A linear relation existed between uterine blood flow and fetal O2 tension. A slightly accelerated decrease in O2 content with a more rapid increase in CO2 tension and [H+] was seen when uterine flow decreased below 150 ml X min-1 X kg fetal wt-1. Following repeated injections fetal descending aortic O2 tension and content decreased 34 and 82% respectively, while PCO2 and [H+] increased 28 and 84% respectively. Placental diffusing capacity for CO increased 117% after repeated embolization. Most of this increase could be accounted for by the fetal hypoxia and acidosis, although some of it may have resulted from distension or recruitment of vessels in the placental exchange area, or a more uniform distribution of placental blood flows. These studies suggest that the acute changes in fetal blood gas values following embolization result from a reduction in blood flow rather than from a reduced placental exchange area.
D000818:Animals; D001794:Blood Pressure; D002248:Carbon Monoxide / Q000378:metabolism*; D004617:Embolism / Q000378:metabolism*; D005260:Female; D005312:Fetal Blood / Q000032:analysis; D008431:Maternal-Fetal Exchange; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D012039:Regional Blood Flow; D012756:Sheep; D014599:Uterus / Q000098:blood supply*
D002248:Carbon Monoxide; D010100:Oxygen