Physiologic study of the uterine venous drainage of the pregnant rhesus monkeys.

The proportion of the total venous drainage from the uterus which represents drainage of the placenta versus myometrial and endometrial drainage has not been defined in any primate. Furthermore, the extent to which this proportion varies in the principal veins draining the pregnant uterus is not known. This information is particularly important in the application of the Fick principle to the determination of uterine blood flows and placental function. In the past a steady diffusion technique involving a constant infusion of a rapidly diffusible solute into the fetal circulation has been applied to the sheep placenta to give measurements of uterine and umbilical blood flows.' In two recent publications, other investigators have applied to the rhesus monkey this method originally developed for the simultaneous measurement of the uterine and umbilical blood flows in sheep.2" Since the method is based upon the Fick principle, its application requires venous blood samples which are representative of the venous drainage of the whole uterus or, alternatively, sufficient information to estimate the composition of the representative venous samples. We shall demonstrate in this paper that in the pregnant rhesus monkey, venous drainage by the two ovarian veins is often unequal in composition and variable. In the light of this finding, we shall examine the uterine flow data that have been published and indicate the systematic errors involved in the calculation of these data.