Placental anatomy and diffusing capacity in guinea pigs following long-term maternal hypoxia.

To determine the relation of placental structure to placental diffusing capacity (DPCO), we exposed Hartley guinea pigs to 12 or 14 per cent O2 from day 15 of gestation to near term (64 days). At that time we measured DPCO and fetal body and placental weights. In addition, we used stereological techniques to measure placental parameters important to diffusing capacity. We also used a mathematical model with results from the stereological measurements to predict the diffusing capacity. In the first hypoxic group (E1), measured DPCO decreased 10.1 +/- 3.7 per cent, while that predicted was 2.4 per cent less than control. Total vascular volume decreased 6.6 +/- 3.6 per cent, while tissue volume and mean diffusion distance increased 10.2 +/- 5.6 per cent and 12.9 +/- 7.0 per cent, respectively. In the pair-fed animals, measured DPCO decreased 22.6 +/- 4.6 per cent, while that predicted was 20.0 per cent less than control. There were no significant stereological differences in this group. In the second (E2) hypoxic group, measured DPCO increased 27.2 +/- 7.4 per cent, while that predicted increased 38.2 per cent. For this same group, total vascular volume increased 11.7 +/- 3.0 per cent, and tissue volume and mean diffusion distance decreased 18.2 +/- 4.6 per cent and 17.8 +/- 3.8 per cent, respectively. These results demonstrate the dependence of placental diffusing capacity upon placental structure.