RIGHT AND LEFT-VENTRICULAR FUNCTION IN FETAL SHEEP EXPOSED TO LONG-TERM HIGH-ALTITUDE HYPOXEMIA

To test the hypothesis that long-term hypoxemia affects fetal cardiac function, we measured right (RVO) and left (LVO) ventricular output by electromagnetic flow probes. We also determined their responses to increased preload (ventricular function curve, VFC) and afterload (arterial sensitivity curve, ASC). We exposed seven pregnant ewes to high altitude (3,820 m) from 30 to 120 days gestation, at which time surgery was performed. Thereafter, maternal arterial PO2 was maintained at approximately 60 Torr by N2 administration. Fetal arterial PO2 was significantly reduced in the hypoxemic fetuses (Hyp, n = 7) compared with that of control (Con, n = 9) (19.3 +/- 0.8 vs. 23.3 +/- 0.5 Torr, P < 0.01). Mean arterial pressures in the Hyp group were elevated (52.0 +/- 1.2 vs. 44.4 +/- 1.7 mmHg, P < 0.01) and fetal heart rate showed minimal change. Catecholamine concentrations in the Hyp group tended to be higher than the Con group, but not significantly so. For Con and Hyp, RVO equaled 275.7 +/- 9.1 vs. 183.1 +/- 10.1 (P < 0.01), LVO equaled 165.7 +/- 16.9 vs. 141.6 +/- 16.5 (NS), and combined ventricular output (CVO) equaled 441.1 +/- 22.9 vs. 334.9 +/- 28.3 ml.min-1.kg-1 (P < 0.05). For the LV there were no significant differences of the VFC between the Con and Hyp groups. However, the right VFC in the Hyp was significantly shifted downward. Concerning afterload, in the RV the slope of the ASC of Con was steeper than that of Hyp (-3.00 +/- 0.05 vs. -0.84 +/- 0.11 ml.min-1.g-1.mmHg-1, P < 0.01). In contrast, in the LV the slopes of the ASC were not significantly different between the Con and Hyp groups. In conclusion, long-term hypoxemia significantly depressed fetal RV function, while only slightly decreasing LV function. RV sensitivity to afterload was decreased. CVO was reduced as a consequence of reduced RVO. The mechanisms responsible for these fetal cardiac alterations remain to be explored.