Measurement of Uterine Blood Flow and Uterine Metabolism

Uterine blood flow has been measured with a chronically implanted miniature electromegnetic flow meter in unanesthetized pregnant sheep and dogs during spontaneous and oxytocin induced labor and followed in the same animal for several postpartum days. In either spontaneous or oxytocin induced labor, uterine contractions are accompanied by a significant decrease in uterine blood flow and relaxations by the return of the flow to or higher than control values. The decrease is roughly proportional to the intensity of uterine contraction. When the contraction is of a tetanic nature and not followed by relaxation, uterine ischemia is so severe that the fetus might succumb. After the delivery of the fetus and before the expulsion of the placenta, uterine blood flow falls slightly. However, after separation and expulsion of the placenta, uterine blood flow falls precipitously. Thereafter, a very slight and progressive decrease continues for several days paralleling uterine involution.

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Increasing Maternal Blood Pressure with Ephedrine Increases Uterine Artery Blood Flow Velocity during Uterine Contraction

Anesthesiology ◽

10.1097/00000542-200203000-00017 ◽

2002 ◽

Vol 96 (3) ◽

pp. 612-616 ◽

Cited By ~ 18

Author(s):

Laurent Ducros ◽

Philippe Bonnin ◽

Bernard P. Cholley ◽

Eric Vicaut ◽

Moncef Benayed ◽

...

Keyword(s):

Blood Flow ◽

Flow Velocity ◽

Uterine Artery ◽

Uterine Contraction ◽

Perfusion Pressure ◽

Resistance Index ◽

Hemodynamic Parameters ◽

Uterine Blood Flow ◽

Uterine Contractions ◽

Uterine Perfusion

Background During labor, ephedrine is widely used to prevent or to treat maternal arterial hypotension and restore uterine perfusion pressure to avoid intrapartum fetal asphyxia. However, the effects of ephedrine on uterine blood flow have not been studied during uterine contractions. The purpose of the study was to assess the effects of ephedrine on uterine artery velocities and resistance index using the Doppler technique during the active phase of labor. Methods Ten normotensive, healthy parturients with uncomplicated pregnancies at term received intravenous ephedrine during labor to increase mean arterial pressure up to a maximum of 20% above their baseline pressure. Peak systolic and end-diastolic Doppler flow velocities and resistance indices were measured in the uterine artery before and immediately after administration of bolus intravenous ephedrine and after ephedrine washout. Umbilical and fetal middle cerebral arterial resistance indices and fetal heart rate were also calculated. Results After ephedrine administration, mean arterial pressure increased by 17 +/- 4%. End-diastolic flow velocity in the uterine artery at peak amplitude of uterine contraction was restored to 74% of the value observed in the absence of contraction. The systolic velocity was totally restored, and the uterine resistance index was significantly decreased, compared with the values in the absence of contraction. Between uterine contractions, ephedrine induced similar but less marked effects. Fetal hemodynamic parameters were not altered by ephedrine administration. Conclusions Bolus administration of intravenous ephedrine reversed the dramatic decrease in diastolic uteroplacental blood flow velocity and the increase in resistance index during uterine contraction, without altering fetal hemodynamic parameters. This suggests that the increase in uterine perfusion pressure during labor could in part restore uterine blood flow to the placenta during uterine contraction.

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Regional blood flow and vascular resistance in response to oxytocin in the pregnant sheep and dog

Journal of Applied Physiology ◽

10.1152/jappl.1961.16.6.1087 ◽

1961 ◽

Vol 16 (6) ◽

pp. 1087-1092 ◽

Cited By ~ 15

Author(s):

N. S. Assali ◽

L. Holm ◽

H. Parker

Keyword(s):

Blood Flow ◽

Vascular Resistance ◽

Regional Blood Flow ◽

Uterine Blood Flow ◽

Pregnant Uterus ◽

Blood Flows ◽

Uterine Contractions ◽

Intravenous Drip ◽

Pregnant Sheep ◽

Regional Vascular Resistance

The effects of oxytocin on regional blood flow and regional vascular resistance were investigated in a group of pregnant ewes and bitches not in labor and in another group in early labor. Single injections or intravenous drip infusion did not change significantly arterial pressure, cardiac output, electrocardiogram, and renal, iliac, femoral, and carotid blood flows in any of the animals studied. The effects on the pregnant uterus were negligible before the onset of spontaneous labor. Only when the animal was in labor did oxytocin produce an increase in uterine contractions accompanied by a significant decrease in uterine blood flow. The data indicate that in the pregnant sheep and dog the circulatory action of oxytocin is limited to the pregnant uterus in labor and that the decrease in blood flow is probably due to an increase in intramural vascular resistance caused by the contracting myometrium around the uterine arterioles. Submitted on May 5, 1961

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Behavioral activity during prolonged hypoxemia in fetal sheep

Journal of Applied Physiology ◽

10.1152/jappl.1988.65.6.2420 ◽

1988 ◽

Vol 65 (6) ◽

pp. 2420-2426 ◽

Cited By ~ 49

Author(s):

A. D. Bocking ◽

R. Gagnon ◽

K. M. Milne ◽

S. E. White

Keyword(s):

Blood Flow ◽

Eye Movements ◽

Normal Incidence ◽

Behavioral Activity ◽

Uterine Blood Flow ◽

Fetal Sheep ◽

Pregnant Sheep ◽

Fetal Breathing ◽

Fetal Breathing Movements ◽

Internal Iliac

Experiments were conducted in unanesthetized, chronically catheterized pregnant sheep to determine the fetal behavioral response to prolonged hypoxemia produced by restricting uterine blood flow. Uterine blood flow was reduced by adjusting a vascular occluder placed around the maternal common internal iliac artery to decrease fetal arterial O2 content from 6.1 +/- 0.3 to 4.1 +/- 0.3 ml/dl for 48 h. Associated with the decrease in fetal O2 content, there was a slight increase in fetal arterial PCO2 and decrease in pH, which were both transient. There was an initial inhibition of both fetal breathing movements and eye movements but no change in the pattern of electrocortical activity. After this initial inhibition there was a return to normal incidence of both fetal breathing movements and eye movements by 16 h of the prolonged hypoxemia. These studies indicate that the chronically catheterized sheep fetus is able to adapt behaviorally to a prolonged decrease in arterial O2 content secondary to the restriction of uterine blood flow.

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The Effects of S(+)-Ketamine and Racemic Ketamine on Uterine Blood Flow in Chronically Instrumented Pregnant Sheep

Anesthesia & Analgesia ◽

10.1213/01.ane.0000096243.74182.5e ◽

2004 ◽

pp. 497-502 ◽

Cited By ~ 18

Author(s):

Danja Str??mper ◽

Wiebke Gogarten ◽

Marcel E. Durieux ◽

Kristian Hartleb ◽

Hugo Van Aken ◽

...

Keyword(s):

Blood Flow ◽

Uterine Blood Flow ◽

Pregnant Sheep ◽

Racemic Ketamine

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Effects of hyperthermia on uterine blood flow and shunting through uterine arteriovenous anastomoses in the late-pregnant ewe

Reproduction Fertility and Development ◽

10.1071/rd99034 ◽

1999 ◽

Vol 11 (5) ◽

pp. 201 ◽

Cited By ~ 1

Author(s):

Suzanne L. Miller ◽

Graham Jenkin ◽

David W. Walker

Keyword(s):

Blood Flow ◽

Experimental Period ◽

Respiratory Alkalosis ◽

Uterine Horn ◽

Arteriovenous Anastomoses ◽

Uterine Blood Flow ◽

Ambient Conditions ◽

Total Blood ◽

Uterine Arteries ◽

Pregnant Sheep

The effect of maternal hyperthermia on uterine blood flow (UBF) through the two main uterine arteries and on the proportion of UBF shunted through uterine arteriovenous anastomoses (AVAs) was investigated. Eight late-pregnant ewes were exposed to normothermic (22–23˚C) or hyperthermic (approx-imately 39˚C) ambient conditions for 8 h. UBF was measured in the left and right uterine arteries using flow probes and microspheres were injected into the uterine artery before, during and after the experimental period. The distribution of microspheres between the uterus and lungs was determined to calculate changes in capillary and AVA blood flows. Hyperthermia produced a significant (P<0.05) increase in maternal core temperature (+1.5˚C), increase in maternal blood pH (+0.21; P<0.05) and decrease in maternal pCO 2 (–16.2 mmHg; P<0.05). Blood flow to the uterine horn ipsilateral to the corpus luteum (CL) remained unchanged during hyperthermia, whereas total UBF and blood flow to the contralateral uterine horn were significantly decreased (P<0.05), by 23.1% and 20.8%, respectively, of pre-heat control values. The proportion of UBF shunted through uterine AVAs during hyperthermia was not significantly different from values observed in normothermic ewes (21.9 0.7%). Mild to moderate hyperthermia in late-pregnant sheep induces respiratory alkalosis and decreases total blood flow to the uterus, brought about by a decrease in blood flow to the uterine horn contralateral, but not ipsilateral to the CL. Heat treatment does not alter the proportion of UBF traversing uterine AVAs.

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Oxygen, glucose, and lactate uptake by fetus and placenta during prolonged hypoxemia

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1995.268.2.r303 ◽

1995 ◽

Vol 268 (2) ◽

pp. R303-R309 ◽

Cited By ~ 5

Author(s):

S. B. Hooper ◽

D. W. Walker ◽

R. Harding

Keyword(s):

Blood Flow ◽

Glucose Uptake ◽

Lactate Clearance ◽

Gravid Uterus ◽

Uterine Blood Flow ◽

Fetal Circulation ◽

Umbilical Blood ◽

Pregnant Sheep ◽

Lactate Uptake ◽

Arterial O2 Saturation

Our aim was to compare the effects of short (4 h) and prolonged (24 h) periods of reduced uterine blood flow (RUBF) on fetal and placental uptake of O2, glucose, and lactate. In pregnant sheep, uterine and umbilical blood flows were measured under normal conditions and after 4 and 24 h of RUBF. A 50% reduction in uterine blood flow caused a 56% reduction in fetal arterial O2 saturation (SaO2). Umbilical blood flow increased from 325 +/- 33 to 378 +/- 32 ml.min-1.kg-1 (P < 0.05) after 4 h but was not different from pre-RUBF values after 24 h. O2 uptake by the gravid uterus was not altered by RUBF, due to an increase (84%) in uterine O2 extraction. Similarly, uteroplacental and fetal O2 consumptions and fetal glucose uptake were not affected by RUBF, whereas uteroplacental glucose uptake was significantly reduced after 4 h (by 42%) and 24 h (by 58%) of RUBF. Fetal lactate uptake was greatly reduced from 78.7 +/- 15.5 to -167 +/- 57 mumol.min-1.kg-1 after 4 h and to -198 +/- 80 mumol.min-1.kg-1 after 24 h of RUBF; negative values indicate placental lactate uptake from the fetal circulation. Thus, although RUBF significantly reduced fetal SaO2, fetal and uteroplacental O2 consumptions did not change. In addition, although fetal glucose uptake was not altered by RUBF, during RUBF the placenta became a major site of lactate clearance from the fetal circulation.

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