Edgar L. Makowski

Blood flow to fetal organs as a function of arterial oxygen content.

In a sheep preparation the blood flow to fetal organs was studied 3 to 10 days after surgery by means of the microsphere technique over a range of fetal arterial O2 content from 6 to 1 mM. Blood flows to neural tissues (cerebrum, cerebellum, brain stem), heart, and the adrenals increased in inverse relation to arterial O2 content. As a result the arterial supply of O2 to these organs tended to remain constant over the O2 range studied. Blood flow to the fetal lungs decreased progressively with hypoxia. The blood flow to kidneys, digestive tract, pancreas, and carcass had a tendency to remain constant or increase gradually in the transition from high to moderately low levels of arterial O2 content and then to decrease abruptly in more severe hypoxia. Umbilical blood flow did not change systematically in relation to arterial O2 content.

Measurement of Umbilical Arterial Blood Flow to the Sheep Placenta and Fetus in Utero: DISTRIBUTION TO COTYLEDONS AND THE INTERCOTYLEDONARY CHORION

A method of estimating the magnitude and distribution of umbilical blood flow by means of radioactive microspheres in sheep fetuses in utero is described. Simultaneous measurements of total umbilical flow by this method and the steady-state diffusion technique showed agreement within ±11%. In 11 fetuses of 90 to 150 days gestational age, the distribution of umbilical flow to the intercotyledonary chorion was 6.2±0.8% of the total. This information has been used to estimate the effect of venous admixture of cotyledonary and noncotyledonary blood on the umbilical vein-uterine vein concentration difference of inert molecules with flow-limited transplacental clearance.

Circulatory Changes in the Reproductive Tissues of Ewes during Pregnancy

The blood flows to reproductive organs were measured by means of radionuclide-labeled microspheres in 24 pregnant ewes with gestational ages ranging from 38 to 141 days. The microspheres were injected

Effect of estrogens on the uterine blood flow of oophorectomized ewes

Abstract Quantitative information about dilatation of uterine blood vessels after administration of estrogens is needed, e.g., the dose response of uterine blood flow to estrogens, whether different estrogens are equipotent in inducing vasodilation, the maximum obtainable blood flow to the nonpregnant uterus under maximum estrogen stimulation, and the related chain of biochemical events. The type of biological preparation developed and the results obtained thus far form the substance of this report.

Effect of estradiol-17β on blood flow to reproductive and nonreproductive tissues in pregnant ewes

The effect of estradiol-17beta (1 mug per kilogram) on regional blood flow and cardiac output was studied by means of radionuclide-labeled microspheres in 6 nonpregnant and 13 pregnant ewes five to seven days after operation. Estradiol caused vasodilation in myometrium, endometrium, and placental cotyledons throughout pregnancy, but these responses were significantly less than the fifteenfold increase seen in the nonpregnant uterine tissues. Significant vasodilation also occurred in the ovaries, cervix, vagina, uterine tubes, mammary gland, skin, and adrenal glands of pregnant ewes. Cardiac output increased by 14%. No significant change in uterine oxygen consumption was associated with the increase in blood flow to the pregnant uterus.

An Evaluation of Fetal Renal Function in a Chronic Sheep Preparation

Fetal renal function in the sheep was investigated in a chronic preparation which permitted repeated evaluations of urine flow and osmolality as well as renal clearances in animals which were unanesthetized and remote from acute surgical stress. Measurements of fetal blood pressure, pH, osmolality, fetal growth in utero, and final outcome did not indicate an adverse effect of the experimental procedure on the fetus. Fetal urine flow and osmolality were highly variable during the early postoperative period. They did not stabilize until 3-6 days after surgery, when urine osmolality became markedly hypotonic (range 65-160 mOsm/kg H(2)O) and urine flow rose to approximately 0.14 ml/min.kg. Fluctuations in urine flow and osmolality in the early postoperative period were the result of tubular reabsorption of water rather than a change in the glomerular filtration rate. The inulin-(14)C clearance, used as a measure of the glomerular filtration rate, was 1.05 +/-0.05 ml/min.kg (mean +/-sem) for all animals studied. Urea, fructose, sodium, and chloride were partially reabsorbed by the fetal kidney, while creatinine was secreted. Continuous drainage of fetal urine for 18 days in one animal demonstrated that the fetus was able to excrete large amounts of water, sodium, and fructose without apparent detrimental effects.

Redistribution of cardiac output and oxygen delivery in the hypoxemic fetal lamb.

In hypoxia, fetal cardiac output and the product arterial O2 content x blood flow to the fetal heart and central nervous system (CNS) tend to remain constant. As a consequence the percentage of cardiac output directed to the heart and CNS increases hyperbolically in inverse relation to the oxygen content of the fetal ascending aorta, [O2]as. The fetal lamb maintains [O2]as approximately 0.45 mM (0.45 +/- 0.02 SEM) higher than the O2 content in the abdominal aorta, [O2]ab, over a wide range of oxygenation. When [O2]as decreases below the 2 mM level, the [O2]as--[O2]ab difference (delta O2) decreases also. A mathematical model of the fetal circulation shows that delta O2 is a function of the ratio oxygen consumption of fetal upper body/abdominal aorta blood flow (VU/FA). The behavior of delta O2 in hypoxia can be explained by assuming that the VU/FA ratio is maintained in moderate hypoxia and decreases in sever hypoxia.

Venous drainage of the human uterus: Respiratory gas studiesin normal and fetal growth-retarded pregnancies

OBJECTIVE To determine respiratory gas relationships between the uterine veins and umbilical vein in normal and pregnancies complicated by intrauterine growth retardation. STUDY DESIGN Respiratory gases were measured in both uterine veins and the umbilical vein in eight normal and 13 pregnancies with intrauterine growth retardation. RESULTS No significant differences were found in the placental versus nonplacental uterine veins. There was a significant correlation for umbilical and uterine venous values of PO2 (p less than 0.002) and PCO2 (p less than 0.004) in appropriate-for-gestational-age pregnancies, umbilical venous PO2 was always less than uterine venous PO2, and PCO2 always greater than uterine. The transplacental gradient was significantly higher in intrauterine growth retarded than appropriate-for-gestational-age pregnancies for both POC2 and PCO2. There was a lower uterine oxygen extraction in intrauterine growth retarded pregnancies (p less than 0.05). CONCLUSION There is no consistent relationship between placental venous drainage in each uterine vein and placental location. The human placenta simulates a relatively inefficient venous equilibrator and the larger transplacental gradients in intrauterine growth retarded pregnancies may reflect differences in both perfusion pattern and placental structure.

Distribution of uterine blood flow in the pregnant sheep

Abstract Uterine flows in 14 pregnant sheep were determined before, during, and after the infusion of radioactive microspheres into the maternal arch of the aorta. The distribution of microspheres in the endometrium, myometrium, and cotyledons was then measured and the regional blood flows to these structures calculated and related to gestational age and fetal weight. As fetal weight increases, the flow to the cotyledons increases markedly, while the flows to the uterine muscle and endometrium show no significant changes.

Effect of Estradiol-17, β on the Magnitude and Distribution of Uterine Blood Flow in Nonpregnant, Oophorectomized Ewes

Extract: In seven nonpregnant sheep studied either acutely or chronically there was an increase in total uterine blood flow after the systemic, 2-min infusion of 1.0