Maternal placental blood flow is reduced in proportion to reduction in uterine driving pressure.

The relationship between uterine driving pressure and maternal placental blood flow was studied after inflation of an aortic occluder previously placed between the renal and ovarian arteries in 10 conscious pregnant rabbits at 28 +/- 1 (mean +/- SEM) d of a 30- to 31-d gestation to test the hypothesis that there is autoregulation of maternal placental blood flow. After control measurements, the femoral artery pressure was reduced 22 +/- 3% from 83 +/- 5 mm Hg and clamped at 65 +/- 4 mm Hg (p < 0.001) for 54 +/- 4 min by servo control. Carotid artery pressure increased from 86 +/- 5 to 98 +/- 6 mm Hg (p < 0.01). There was no change in cardiac output (839 +/- 78 vs 814 +/- 64 mL/min; NS), upper-body flow (651 +/- 62 vs 671 +/- 55 mL/min; NS), or renal flow (111 +/- 14 vs 104 +/- 8 mL/min; NS). Blood flow to tissues below the occluder decreased from 188 +/- 18 to 143 +/- 14 mL/min for the lower body (p < 0.05), 153 +/- 15 to 116 +/- 11 mL/min for the hindquarters (p < 0.05), and 17.7 +/- 1.9 to 12.9 +/- 1.4 mL/min for 13 pregnant uterine horns (p < 0.05). Placental flow to live fetuses per horn decreased from 13.0 +/- 1.9 to 8.9 +/- 1.2 mL/min (p < 0.01), whereas there was no significant change in myoendometrial flow (4.0 +/- 0.3 vs 3.5 +/- 0.5 mL/min; NS). Uterine oxygen consumption was unchanged (1.15 +/- 0.16 vs 1.06 +/- 0.13 mL/min; NS).(ABSTRACT TRUNCATED AT 250 WORDS)