Cardiac function in fetal sheep during two weeks of hypoxemia.

Although several studies have examined fetal cardiac responses to acute hypoxemia, relatively little is known of the response to prolonged hypoxemia. To determine the effects of long-term hypoxemia on ovine fetal cardiac function, we measured right (QRV) and left ventricular outputs (QLV) and determined the effects of increasing preload (ventricular function curve) and afterload (arterial pressure sensitivity curve) on the left ventricle. Six days after fetal surgical instrumentation with catheters and electromagnetic flow probes (approximately 123 days gestation), we administered N2 into the maternal trachea for 14 days to reduce maternal PO2 to approximately 55 Torr (hypoxemic group, Hyp, n = 6). Normoxic animals were used as controls (Cont, n = 6). With the onset of hypoxemia, fetal arterial PO2 was reduced from approximately 27 to approximately 18 Torr. Fetal heart rate in Hyp fetuses decreased approximately 22% on day 14 compared with Cont (P < 0.05). Mean arterial pressure in the Hyp group was higher than that of Cont but not significantly so. Right and left atrial pressures were not affected by hypoxemia. QRV in Hyp fetuses was maintained on day 1 but decreased significantly by day 3 (approximately 19%) and further decreased on days 7 (approximately 28%) and 14 (approximately 34%). QLV was not depressed until day 7 (approximately 20%), with a further decrease on day 14 (approximately 38%). In association with the decreased QLV the plateau of the ventricular function curve in Hyp fetuses was depressed significantly on days 7 and 14. In contrast, the slope of the arterial pressure sensitivity curve in the Hyp group did not differ from Cont.(ABSTRACT TRUNCATED AT 250 WORDS)