Foetal placental blood flow in the lamb

Abstract

SUMMARY1. Fifteen sheep foetuses of 1-5-5-2 kg body weight were prepared with indwelling arterial and venous catheters for experimentation one to six days later.2. Unanaesthetized foetuses were found to have mean arterial and central venous blood pressures of 40 + 1-5 (S.E. of mean) and 2x0 + 0-3 (S.E. of mean) mm Hg respectively, compared to intra-uterine pressure. Intra-uterine pressure was 16 + 0-8 (S.E. of mean) mm Hg with respect to atmospheric pressure at mid-uterine level.3. Mean placental blood flow of the foetuses was 199 + 20 (S.E. of mean) ml./(min. kg body wt.). Mean cardiac output in eleven of the foetuses was 658 + 102 (S.E. of mean) ml./(min.kg).4. Mean foetal and maternal colloid osmotic pressures were 17'5+ 0 7 (S.E. of mean) and 20-5 + 0-6 (S.E. of mean) mm Hg respectively at 380 C.5. Intravenous infusions into six ewes of 1P8 mole of mannitol and 0 4 mole of NaCl resulted in significant increases in foetal plasma osmolarity, sodium, potassium, and haemoglobin concentrations, without detectable transfer of mannitol to the foetal circulation.6. In the sheep placenta there is osmotic and hydrostatic equilibration of water. As a consequence, there should be an interaction between foetal placental blood flow and foetal water exchange with the maternal circulation. It was concluded that this interaction tends to stabilize foetal placental blood flow.

Novel modification of an artificial placenta: pumpless arteriovenous extracorporeal life support in a premature lamb model

“…Therefore, the circuit volume of our artificial placenta (60 ml) may be sufficiently low. However, the resistance of our membranous oxygenator (0.85 mmHg·min·kg·ml −1 ) may still be too high, as the placental resistance of sheep was previously reported to be 0.14-0.30 mmHg·min·kg·ml −1 (9,11,12). If an artificial placenta with a lower resistance can be developed, such a device may further prolong fetal survival time by reducing afterload to the fetal heart.…”

“…Figure 1 shows the changes in physiologic parameters over time in the longest survivor. At 4 h after birth, a significant decrease in circuit blood flow, to ~15% of normal sheep placental blood flow (9), and a marked increase in blood lactate level were observed; gas exchange in the membranous oxygenator was maintained. We administered dopamine to the fetus to increase circuit blood flow via an inotropic cardiac effect and vasoconstriction, but administration had to be discontinued 4 h later because of a further increase in blood lactate level.…”

Changes in fetal renal function in response to infusions of a hyperosmotic solution of mannitol to the ewe.

“…Thus, it is not surprising that the fetal kidney usually produces a urine that is hypo-osmotic with respect to plasma. However, transplacental water transfer is dependent upon hydrostatic and osmotic gradients across the placenta (Faber & Green, 1972) and it is possible that these gradients may be altered by modifying maternal fluid intake or, in the sheep, by ingestion of large amounts of dry feed. When these perturbations occur, maintenance of the fetal blood volume and its osmolality within normal limits may depend on rapid adjustments in fetal renal function.…”

“…infusion of mannitol. Mannitol does not cross the sheep placenta (Faber & Green, 1972). The renal responses of the fetal lambs were measured following i.v.…”

“…infusion of mannitol to the ewe. This rise in fetal plasma osmolality probably resulted from the reduction in net transplacental water transfer (see Faber & Green, 1972) which also elicited a rapid change in fetal renal function, in that fetal urine flow rate dropped within 90 min of infusion of mannitol. Because free water clearance fell and urinary sodium excretion rose (Table 1, Figs.…”