Abstract
We used the microsphere method to assess the effect of increasing UV blood O2 on fetal cardiac output (CO) and vascular shunts by giving the ewe 100% inspired oxygen (MO2). Two groups of fetal lambs with normal pH were studied; 5 had normal aortic PO2 (20.4±2.4) and 5 were spontaneously hypoxemic (12.0±2.0). Although magnitude of shunts differed in the two groups, they changed in similar direction so the two groups were analyzed together. UV Hgb O2 saturation increased from 61.6±20.7 to 85.5±15.8% (p<0.005) during MO2. CO and umbilical blood flow (UBF) did not change from control values of 537±82 and 208±30 ml/min/kg. 59.7±6.6% of UV blood passed through the ductus venosus (DV); this did not change with MO2. The percent DV blood crossing the foramen ovale to enter the upper body decreased from 38.5±8.7 to 23.5±5.5% (p<0.001) and the percent DV blood returning to the placenta without perfusing the fetal body increased from 32.1±5.8 to 37.9±8.0% (p<0.05). Lung blood flow as percent of CO increased from 4.9±3.6 to 13.8±6.4 (p<0.005) during MO2. Thus, increasing UV O2 modifies shunting of DV blood through the foramen ovale and to the placenta; this probably results from the decrease of pulmonary vascular resistance. (Supported by NIH grants HL 06285 and HL 24056.)
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