27 CARDIOVASCULAR RESPONSES OF THE INTRAUTERINE GROWTH RETARDED FETUS (IUGR) TO ACUTE HIPOXEMIA

Abstract

IUGR fetal lambs with chronic hypoxemia are particularly susceptible to additional acute stress. We therefore studied the cardiovascular responses of 6 IUGR fetuses to superimposed acute hypoxemia. IUGR was produced by daily embolization of the uteroplacental vascular bed. Additional acute fetal hypoxemia (PaO211 torr) was produced by the ewe breathing a 10% O2,and nitrogen gas mixture. Fetal cardiac output (CO) and its distribution was measured using radioactive microspheres. Basal umbilical blood flow (Q) was reduced in the IUGR fetuses (132±18 ml · min-1 · kg-1; mean ± SE), and kidneys, and adrenal Q (ml × min-1 × 100 g-1) elevated. During the acute hypoxemic episodse, Q increased to myocardium (478 ± 209 to 732 ± 248) and to the brain (238 ± 79 to 295 ± 69) with a trend to further increase in adrenal blood flow (588 ± 88 to 1001 ± 329). These increased organ Q changes were similar to those occurring in normal fetuses but reached greater absolute levels.There was also a decrease in Q to the gut, kidneys and carcass, but no change in CO nor the depressed umbilical Q. The Q to the carcass in the IUGR fetus during acute hypoxemia is greater than the Q observed in the normal fetus. The inability of the IUGR fetus to increase their abnormally low umbilical Q, plus its inability to reduce the carcass Q,as the normal fetus does, may account for the increased mortality rate observed in the IUGR fetus under acute hypoxemia.