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A model for studying chronic reduction in uterine blood flow in pregnant sheep.

A model is described for the investigation of the effects of acute and chronic reduction in uterine blood flow in unanesthetized pregnant sheep. An externally adjustable vascular occluder has been designed to utilize the principles of a modified Goldblatt clamp. This occluder is made of nonbreakable plastic and is adjusted via a flexible cable encased in a sheath. The occluder has been tested in 17 pregnant sheep and has remained functional for periods up to 36 days, the length of implantation. This occluder has allowed graded reductions in uterine blood flow, which can be accurately and consistently reproduced. An example of flow reduction is shown in which uterine blood flow has been reduced by 24, 47, and 82% in late-term pregnant sheep. This method will allow the investigation of the effects of uterine hypoperfusion and fetal hypoxia in a precisely controlled unanesthetized pregnant sheep preparation.