M. Kamitomo et al., CARDIAC-FUNCTION IN FETAL SHEEP DURING 2 WEEKS OF HYPOXEMIA, The American journal of physiology, 266(6), 1994, pp. 180001778-180001785
Although several studies have examined fetal cardiac responses to acut
e hypoxemia, relatively little is known of the response to prolonged h
ypoxemia. To determine the effects of long-term hypoxemia on ovine fet
al cardiac function, we measured right (Q(RV)) and left ventricular ou
tputs (Q(LV)) and determined the effects of increasing preload (ventri
cular function curve) and afterload (arterial pressure sensitivity cur
ve) on the left ventricle. Six days after fetal surgical instrumentati
on with catheters and electromagnetic flow probes (similar to 123 days
gestation), we administered N-2 into the maternal trachea for 14 days
to reduce maternal PO2 to similar to 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 similar to 27
to similar to 18 Torr. Fetal heart rate in Hyp fetuses decreased simil
ar to 22% on day 14 compared with Cont (P < 0.05). Mean arterial press
ure in the Hyp group was higher than that of Cont but not significantl
y so. Right and left atrial pressures were not affected by hypoxemia.
Q(RV) in Hyp fetuses was maintained on day 1 but decreased significant
ly by day 3 (similar to 19%) and further decreased on days 7 (similar
to 28%) and 14 (similar to 34%). Q(LV) was not depressed until day 7 (
similar to 20%), with a further decrease on day 14 (similar to 38%). I
n association with the decreased Q(LV) the plateau of the ventricular
function curve in Hyp fetuses was depressed significantly on days 7 an
d 14. In contrast, the slope of the arterial pressure sensitivity curv
e in the Hyp group did not differ from Cont. Fetal growth rate in Hyp
fetuses was significantly depressed compared with Cont. In conclusion,
2 wk of hypoxemia during the last third of gestation significantly de
pressed LV function but did not affect LV sensitivity to afterload. Q(
RV) was decreased significantly by day 3, whereas Q(LV) was not decrea
sed until day 7. The mechanisms for this difference in response remain
to be explored.