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The effect of intravenous infusion of angiotensin II (2 to 200 ng/kg/min) on uterine blood flow and cardiovascular performance was studied in the normotensive, unanesthetized pregnant ewe. With low rates of infusion (2 to 4 ng/kg/min), only a transient increase in uterine blood flow, lasting 1 to 3 minutes, was observed. Higher rates (110 to 200 ng/kg/min) of infusion caused a decrease in uterine blood flow; this decrease was significantly correlated to the dose. Angiotensin II also caused a significant decrease in the maternal heart rate and an increase in mean maternal arterial blood pressure as the rate of infusion was increased. A high rate of infusion resulted in decreased fetal heart rate and PaO2, probably due to a marked reduction in uteroplacental blood flow.

The effect of magnesium sulfate on fetal heart rate (FHR) variability and uterine activity is evaluated in 19 preeclamptic patients at term in active labor. Magnesium sulfate was given by intramuscular injection in nine patients and by intravenous infusion in 10 patients after an intravenous loading dose over a period of 15 minutes. No significant change was noted in FHR variability. There was only a transient, mild decrease in the frequency of uterine contractions during the magnesium sulfate loading dose, and there was no significant change in the intensity of uterine contractions. The conclusion is that, when magnesium sulfate is used for treatment of mild preeclampsia in patients at term in established labor, there is no clinically significant effect on FHR variability or uterine activity.

An on-line technique for quantitating uterine activity by measuring the total area under the intrauterine pressure curve was utilized during the labor of 100 primiparous patients. Uterine activity was measured in uterine activity units (1 UAU=1 Torr minute). UAU's were calculated for each patient in both cumulative and noncumulative fashions. The rate of uterine activity (UAU per unit of time) increased as labor progressed, yet the total UAU's expended at each centimeter of dilatation progressively decreased with advancing dilatation. Thus, the rate of cervical dilatation increased faster than could be accounted for by the increase in uterine activity. The implication being that the efficiency of uterine contractions increases with advancing labor. It no longer appears reasonable to refer to labor in terms of elapsed time. Information regarding the "pattern of cervical dilatation" and uterine activity appears to be much more meaningful to the evaluation of progress in labor. Quantitation of uterine activity may provide useful information for the ongoing management of labor. Quantitation of UA does provide a means of evaluating the effects of specific events such as medication, anesthesia, and manipulation on UA.