A balanced field-type electromagnetic flowmeter

Heat flux and oxygen consumption of the pregnant uterus

Heat flux (conductive and convective heat) and oxygen consumption of the pregnant uterus and its content were measured simultaneously in the same group of pregnant ewes during the acute postoperative period, during a chronic resting period, and during alpha- and beta-adrenergic-receptor stimulation with norepinephrine and ritodrine. Results indicated four conclusions. First, an excellent correlation existed between heat flux and oxygen consumption in the acute and chronic resting condition as well as during increasing uteroplacental vascular resistance and decreasing blood flow produced by norepinephrine infusion; the correlation was not as good during ritodrine infusion. Second, during rest, about 85% of heat generated by the pregnant uterus is eliminated through the uteroplacental circulation while the remaining heat diffuses through the myometrium. Third, during decreasing uteroplacental blood flow and elevated resistance, the pregnant uterus is able to maintain a normal thermostasis by widening the temperature difference in the blood entering and leaving the uterus and by increasing the myometrial heat exchange; oxygen consumption also is maintained at normal level through increase in oxygen extraction. Fourth, with the exception of uteroplacental circulation, the circulatory, metabolic, and thermal conditions of the pregnant ewe are not different after 5 hours from 5 to 7 days after the surgical procedure.

Hemodynamic effects of isoxsuprine and terbutaline in pregnant and nonpregnant sheep

Nonpregnant and pregnant sheep at 110 to 140 days' gestation were chronically instrumented for measurement of mean arterial pressure, heart rate, cardiac output, common internal iliac artery blood flow, and middle uterine artery blood flow. Systemic and regional vascular resistances were calculated from pressure/flow data. Either isoxsuprine, 10 microgram/kg/min, or terbutaline, 0.40 microgram/kg/min, was infused continuously for a period of one hour. The above-mentioned parameters were monitored during control, infusion, and postinfusion periods. The findings show that: (a) isoxsuprine had greater effects on the mean arterial pressure, heart rate, and cardiac output than did terbutaline; (b) both agents had minimal effects on the common internal iliac artery blood flow of pregnant ewes, but isoxsuprine decreased the middle uterine artery blood flow significantly; and (c) with isoxsuprine, a marked vasodilatation occurred in the common internal iliac vascular bed of nonpregnant ewes, in contrast to the insignificant changes in the pregnant ewes. The conclusions drawn were that: (1) the more pronounced effects of isoxsuprine are most probably related to a greater beta 1 stimulation; (2) contiguous regional vascular beds respond differently to pharmacologic stimuli; and (3) the state of a given vascular bed during the resting state determines its response to vasoactive agents.

Renal hypertension and pregnancy in the sheep. I. behavior of uteroplacental vasomotor tone during mild hypertension

The progressive changes in arterial pressure and uteroplacental hemodynamics were studied in 13 pregnant sheep from about the eightieth gestational day. All animals were followed to term. The results revealed a progressive increase in uteroplacental blood flow as the pregnancy progressed in the seven control animals. In six of the animals, mild hypertension was induced by unilateral renal artery constriction at about the one hundred fifteenth day. Following the induction of mild hypertension, there was a transient increase in uteroplacental vascular resistance and a reduction in uteroplacental blood flow. The arterial pressure remained significantly increased throughout the remainder of the gestation.