Reference resistance indices of the umbilical, fetal middle cerebral and uterine arteries at 24-42 weeks of gestation

The objective of this cross-sectional study was to construct new reference ranges for Doppler flow velocity waveform resistance indices for the fetal umbilical artery, middle cerebral artery, placental and non-placental uterine arteries and the placentocerebral ratio in a large and minimally selected population attending a single clinic. Study design and data analysis adhered to a number of stringent and validated methodological recommendations derived both from the recent literature and from a review of earlier publications in this field. The final database comprised initial routine Doppler velocimetry at 24-42 weeks' gestation in 1675 pregnancies. Separate regression models were fitted to estimate the mean and standard deviation at each gestational age for each vessel. New charts, centile tables and regression equations are presented for the resistance indices of the fetal umbilical artery, middle cerebral artery, placental and non-placental uterine arteries and the mean of both uterine arteries and for the placentocerebral ratio.

Increase of fetal hematocrit decreases the middle cerebral artery peak systolic velocity in pregnancies complicated by rhesus alloimmunization

Our hypothesis for this study was that an increase in fetal hematocrit would decrease the middle cerebral artery peak systolic velocity. Seventeen pregnancies complicated by Rh alloimmunization were included in this study. Middle cerebral artery peak systolic velocity was studied by Doppler ultrasound before and after intrauterine transfusion with adult packed red blood cells (hematocrit = 80-85%). Mean gestational age at time of study was 27 weeks. Paired t-test was used for statistical comparison. A P value of < 0.05 was considered statistically significant. The fetal hematocrit ranged from 5.9% to 30% prior to the procedure, and it was 24.8-53.4%, following the procedure. Mean middle cerebral artery peak systolic velocity was 46.2 +/- 10.7 cm/s prior to the procedure, and it decreased to 31.7 +/- 9.5 cm/s following the procedure (P < 0.01). The increase of fetal hematocrit significantly decreases the middle cerebral artery peak systolic velocity supporting data that this Doppler measurement may be useful for the diagnosis of fetal anemia.

Changes in umbilical artery, middle cerebral artery, and aorta blood flow Doppler waveform pulsatility indices after funisocentesis

This study evaluates the effect of funisocentesis on umbilical artery, fetal cerebral artery, and aortic circulation. The pulsatility index in the umbilical artery, fetal middle cerebral artery, and descending aorta was measured by pulsed Doppler ultrasonography before and after 41 diagnostic funisocenteses. Percutaneous umbilical artery blood sampling was associated with a significant decrease in umbilical artery pulsatility index (mean -0.132, standard deviation 0.259, P = 0.002) and in middle cerebral artery pulsatility index (mean -0.143, standard deviation 0.260, P = 0.001). The decline in resistance to flow of the umbilical artery (r = 0.340, P = 0.029) and middle cerebral artery (r = 0.457, P = 0.002) was correlated with gestational age at sampling. These findings suggest that alterations in the waveforms from both the umbilical and the fetal cerebral circulations can be induced by fetal blood sampling.

Intracavernous anterior cerebral artery origin with associated arteriovenous malformations: a developmental analysis: case report

OBJECTIVE AND IMPORTANCE

This case demonstrates an unusual association between arteriovenous malformations and an intracavernous anterior cerebral artery origin. To the best of our knowledge, this relationship has not been previously described. Identification and understanding of this relationship are important in pre-embolization and surgical planning and in offering some insight into neurovascular development.

CLINICAL PRESENTATION

The patient presented with severe recurring headaches and an otherwise nonfocal neurological examination. He maintained a stable neurological course throughout evaluation and therapy.

INTERVENTION

The patient underwent endovascular embolization of the arteriovenous malformations without consequence. He was then scheduled for radiosurgical treatment planning.

CONCLUSION

This case demonstrates an unusual neurovascular anomaly with associated arteriovenous malformations. To the best of our knowledge, this is the first reported case of such an association. An understanding of anomalous angioarchitecture and neurovascular development is essential for prudent endov ascular and surgical planning.

High altitude-induced changes in alpha1-adrenergic receptors and Ins(1,4,5)P3 responses in cerebral arteries

In response to high-altitude long-term hypoxemia, the cerebral arteries of fetal and adult sheep show decreased contractile responses to norepinephrine (NE) and other agonists. To test the hypothesis that hypoxia-induced developmental and vessel specific cerebral artery contractility changes are mediated, in part, by changes in alpha1-adrenergic receptor (alpha1-AR) density and/or NE-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] responses, we performed the following study. In common carotid (Com) and main branch cerebral (MBC) arteries from normoxic adult ewes and near-term fetuses and those acclimatized to high altitude (3,820 m), we quantified alpha1-AR density (maximal binding in fmol/mg protein) and affinity (dissociation constant in nM) with the alpha1-AR antagonist [3H]prazosin. In addition, we quantified NE-induced Ins(1,4,5)P3 responses in these arteries. With long-term hypoxemia, alpha1-AR density in fetal and adult Com decreased 75% (from 113 +/- 18 to 28 +/- 5 fmol/mg protein) and 66% (from 54 +/- 3 to 18 +/- 4 fmol/mg protein), respectively, from normoxic control values. alpha1-AR density of the fetal and adult MBC decreased 76% (from 47 +/- 4 to 11 +/- 1 fmol/mg protein) and 61% (from 23 +/- 3 to 9 +/- 3 fmol/mg protein), respectively, from controls. In hypoxemic adult Com, the NE-induced Ins(1,4,5)P3 response decreased 51% (from 309 +/- 38 to 151 +/- 24%) from the control value. In fetal and adult MBC, long-term hypoxemia was associated with decreases of 35% (from 345 +/- 40 to 225 +/- 30%) and 44% (from 355 +/- 55 to 199 +/- 16%), respectively, from control values. We conclude that in the adult Com and MBC vessels, acclimatization to high-altitude, long-term hypoxemia was associated with significant decreases in both alpha1-AR density values and Ins(1,4,5)P3 responses to NE. Similarly, in the fetal MBC arteries, high-altitude hypoxemia was associated with marked attenuation of both alpha1-AR density and NE-induced Ins(1,4,5)P3 responses. The magnitude of decreases in NE-induced Ins(1,4,5)P3 responses in these vessels correlated fairly well with the decreases in alpha1-AR density. These findings suggest that changes in noradrenergic receptor-second messenger coupling may play a role in altered cerebrovascular tone in association with high-altitude acclimatization and other forms of long-term hypoxia in both fetus and adult.

Middle cerebral artery velocimetry as a predictor of hypoxemia in fetuses with increased resistance to blood flow in the umbilical artery

About half of all fetuses with increased resistance to blood flow, but with still detectable diastolic blood velocity in the umbilical artery (UA), show signs of imminent asphyxia during labour indicating a need for operative delivery. Fetal brain-sparing during hypoxia is characterized by an increase in diastolic and mean blood flow velocity in the middle cerebral artery (MCA). The aim of this study was to assess whether MCA blood velocity in pregnancies with increased resistance to blood flow in the feto-placental circulation could predict the development of fetal asphyxia during labour. Fifty pregnant women with signs of increased feto-placental vascular resistance between 31 and 42 weeks of gestation were studied serially by Doppler ultrasound and the last examination was correlated to perinatal outcome. The MCA pulsatility index (PI), cerebroplacental PI ratio and mean MCA blood velocity were calculated and correlated to fetal outcome. Fetal brain-sparing was defined as MCA PI < mean -2 S.D., cerebroplacental PI ratio < 1.08 and mean MCA blood velocity >mean + 2 S.D. No significant association was found between signs of fetal brain-sparing and the perinatal outcome. Among fetuses with signs of increased resistance to flow in the umbilical artery, velocimetry of the middle cerebral artery did not identify those that would not withstand the strain of labour.

Circulatory Doppler parameters in fetal hypoxaemia

A 32-year-old pregnant woman (gravida 1, para 0) was delivered at 27 weeks of gestation by elective Caesarean section because of regular fetal heart rate (FHR) decelerations. Doppler ultrasound assessment of the middle cerebral artery (MCA) and the ductus venosus (DV) showed pathological results, whereas the umbilical artery waveforms were normal. Blood gas analysis of the umbilical cord obtained at Caesarean section indicated fetal hypoxaemia. The discrepancy between abnormal Doppler findings in the central circulation and normal Doppler in the umbilical artery suggests that a detailed Doppler assessment may be necessary in order to clarify abnormal FHR tracings.

Formation of the ocular arteries in the chick embryo: observations of corrosion casts by scanning electron microscopy

An investigation was carried out on the formation of the blood vessels that supply the optic cup or eyeball in developing chick embryos ranging in age from Hamburger-Hamilton stage 17 (st17) to st44. Corrosion casts of the vasculature were made by injecting resin and examined by scanning electron microscopy. The optic cup was supplied by branches of the cranial ramus of the circle of Willis (CCW) from st17 to st19. By st23, a branch of the CCW and that of the internal carotid artery became anlagen of two ophthalmic arteries, namely, the cerebral ophthalmic artery (COA) and the internal carotid ophthalmic artery (ICOA) respectively. They were continued by primordia of the long posterior ciliary arteries, which connected with each other to form a ring around the pupil. Between st19 and st26, another branch of the CCW was found, by contrast, to supply the primitive pecten. The distal part of the nasal long posterior ciliary artery began to atrophy at st28, so the temporal long posterior ciliary artery only began to supply the ring artery around the pupil by st30. At the same time, the artery supplying the pecten became anastomosed with the ICOA behind the eyeball to form the definitive pectinate artery. By st30, the ophthalmic branch of the stapedial artery had also formed and connected with the distal part of the ICOA behind the eyeball, as well as with the distal part of the COA by st34. The supraorbital branch of the stapedial artery, which had replaced the CCW to anastomose with the ethmoidal artery by st30, was found to be connected to the COA at st36. The main vascular system supplying the eyeball was complete at st36, and its structure at st40 and st44 was fundamentally similar to that at st36.

[Pulsatility indexes of fetal middle cerebral artery and umbilical artery for predicting intrauterine fetal growth retardation]

OBJECTIVE

To evaluate the role of fetal cerebral and umbilical blood flow for predicting intrauterine fetal growth retardation (IUGR).

METHODS

Doppler ultrasonography was used to study pulsatility indexes (PI) of the fetal middle cerebral artery (MCA) and umbilical artery (UA) in 84 normal late pregnancies and 31 IUGR cases.

RESULTS

MCA PI were significantly lower in IUGR fetuses than that of normal fetuses (P < 0.01). UA PI and UA PI/MCA PI ratio were higher in IUGR group than that of normal group (P < 0.01). The sensitivities of MCA PI, UA PI and UA PI/MCA PI ratio for predicting IUGR were 80.64%, 70.96% and 87.09% respectively at the cut off level with 2 standard deviation (SD). The specificities were 94.05%, 88.90% and 97.61% respectively.

CONCLUSIONS

Doppler ultrasonography for predicting IUGR was a practical and sensitive method.

Prediction of perinatal outcome by middle cerebral artery Doppler velocimetry

The relationship between pulsatility index (PI) in the middle cerebral artery (MCA) and adverse perinatal outcome was studied in 162 normal and 75 high-risk pregnancies. The intrapartum cardiotocographic (CTG) findings, the mode of delivery, 1 and 5-minute Apgar scores, the pH level of the umbilical artery, admission to the neonatal intensive care unit (NICU) and the incidence of intrauterine fetal growth retardation were recorded. In the low risk group, the PI values in the MCA were only affected in growth retarded fetuses (P = 0.0084). In the high-risk group, there was an association between the MCA PI values and 5-minute Apgar scores (P = 0.0397), umbilical artery pH values (P = 0.0068) and development of IUGR (P = 0.0376). In both groups, an abnormal intrapartum CTG, the 1-minute Apgar score, cesarean section for fetal distress and admission to the NICU were not related to PI values in the MCA. Our present study suggests that Doppler flow measurement of MCA provides useful information about perinatal outcome, especially in the high-risk pregnancies.

Neurovascular developmental interaction: a specific form of vascular maldevelopment in the malformed brain. I. An experimental study and proposal of a new teratological concept

The process of the development of the intracranial vessels was studied by means of immunohistochemical analysis of factor VIII in normal and exencephalic chick fetuses. The results revealed that the development of blood vessels in exencephalic brain was far advanced beyond the norm, with intense immunoreactivity to factor VIII on postincubation day 16 exceeding that on day 21 in normal controls. Compared with results regarding the direction of the overgrowth in the neuronal maturation process in the previous study using the chick exencephaly model, the findings of overmatured blood vessels were compatible with NSE- and somatostatin-positive elements that appeared especially in the overgrowth foci. The results of the present study suggested the pathogenic development of the "area cerebrovasculosa" in the neural placode as a phenomenon consequent upon hypervascularization in response to neuronal overgrowth, as seen in human cases of exencephaly or anencephaly. We emphasize the significance of this specific phenomenon in the development of the fetal central nervous system, namely neurovascular developmental interaction.

'Medial defects' in the prenatal human cerebral arteries: an electron microscopic study

BACKGROUND AND PURPOSE

Fine structural studies were performed to investigate the histogenesis of human intracranial arteries. Special attention was paid to whether "medial defects" exist in these arteries.

METHODS

Segments of the intracranial extracerebral arteries of normal human embryos (n=6) were examined with transmission electron microscopy.

RESULTS

Focal defects of the medial smooth muscle cells were disclosed at every bifurcation of the developing arteries. This configuration persisted until the arteries obtained enough muscle coat. These areas, in which an absence of medial smooth muscle cells (ie, a medial defect) existed, were occupied by fibrous connective tissues of elastin and collagen.

CONCLUSIONS

The medial defect observed at the arterial bifurcation of the embryos seems to be a development process that accompanies human ontogenesis rather than a congenital anomaly, supporting a possible pathogenesis for intracranial saccular aneurysms.

Fetal middle cerebral artery blood flow velocities in pregnancies complicated by intrauterine growth restriction and extreme abnormality in umbilical artery Doppler velocity

If they are not delivered in a timely fashion, pregnancies complicated by severe intrauterine growth restriction (IUGR) can lead to fetal loss. Conventional fetal well-being tests, including ultrasound measurement of fetal growth rate, biophysical profile, nonstress test, and contraction stress test are used to manage these pregnancies. Some fetuses delivered based on abnormal fetal well-being tests show long-term sequelae. A better understanding of the malfunction of the placenta and its effect on the fetus is desperately required for better management of these cases. We are reporting our experience of 6 such pregnancies followed by fetal middle cerebral artery (MCA) blood flow velocity measurements. There was significant decrease in MCA flow velocities in all of these fetuses compared to normal population (p < 0.05). Reverting to normal values occurred prior to the appearance of abnormal conventional tests, on average 4 days earlier. In other words, normalization of MCA flow velocities was a harbinger of fetal jeopardy. Although our observation includes a small number of patients, there is a potential for use of MCA blood flow velocity measurement to aid us in understanding and managing fetuses with IUGR. This needs to be evaluated in a larger study.

Effect of dehydroepiandrosterone sulfate on fetal middle cerebral artery flow velocity waveforms in term pregnancy

OBJECTIVE

To investigate whether bolus injection of dehydroepiandrosterone sulfate (DHAS) is associated with changes in fetal middle cerebral artery flow velocity waveforms in term pregnancy.

METHODS

Ten normal full-term pregnant women received the administration of a 200-mg intravenous dose of DHAS in 20 ml of 5% dextrose. Ten normal full term pregnant women received 20 ml 5% dextrose as controls. Color Doppler flow imaging and pulsed Doppler ultrasonographic assessments were made on fetuses in each group before and 10 min, 30 min, 60 min, 90 min. and 120 min after DHAS or dextrose administration. The pulsatility index (PI) values for the middle cerebral artery, and umbilical artery, and fetal heart rate were recorded.

RESULTS

In the DHAS group, middle cerebral artery PI decreased from baseline by 24% (p<.05) after 10 min, and the mean reduction was 22% (p<.05) after 30 min. The PI returned to the baseline value 60 min later. In the control group, there was no change in middle cerebral artery PI. No change was found in umbilical artery PI or fetal heart rate in the control or DHAS group.

CONCLUSION

DHAS induces a significant decrease in the fetal middle cerebral artery PI, which suggests a possible decrease in fetal cerebral vascular impedance in term pregnancy.

Assessment of early placental development in the cynomolgus monkey (Macaca fascicularis) using colour and pulsed wave Doppler sonography

Colour flow mapping and pulsed wave Doppler were used to assess the process of placental growth and development in the cynomolgus monkey from 32 to 71 days gestational age. Fetal and maternal vessels were reliably visualised and insonated. Accurate longitudinal non-invasive assessment of placentation is possible using this technique.

Doppler velocimetry of the fetal middle cerebral and renal arteries: interobserver reliability

Using color and pulsed Doppler ultrasonography, the interobserver reliability of measurements in the fetal circulation was evaluated in 41 pregnancies of 25 to 39 weeks' gestation. Two observers recorded flow velocity waveforms from the middle cerebral and renal arteries for measurement of peak systolic, minimum diastolic, and mean velocities, pulsatility index, and resistive index. Intraclass correlation coefficient of reliability was calculated by analysis of variance. Substantial interobserver agreement was found for pulsatility index and minimum diastolic velocity in both arteries. Therefore, these measurements have the greatest clinical applicability.

[Significance of middle cerebral artery doppler velocimetry based on behavioral states in intrauterine growth retarded fetuses--prediction of development of fetal distress]

Middle cerebral artery resistance indices (MCARI) based on fetal behavioral states were calculated in 60 normal and 20 intrauterine growth retarded (IUGR) fetuses between 33 and 40 weeks of gestational age. Fetal behavioral states were determined by recording fetal actocardiograms. The results obtained were as follows: 1. MCARI was significantly lower in the active phase than in the resting phase in normal fetuses. 2. Of the 20 IUGR fetuses, 9 subsequently developed fetal distress. Seven of 11 fetuses who did not develop fetal distress had abnormally low MCARI (less than M-2.0 SD) in the active phase. On the other hand, seven of the fetuses that subsequently developed fetal distress had abnormal MCARI not only in the active phase but also in the resting phase. The fetuses that did not develop fetal distress had different MCARIs in the two phase, but the fetuses that developed fetal distress exhibited no such difference. 3. The sensitivity and specificity in predicting the development of fetal distress in IUGR fetuses with abnormal MCARI in the resting phase were 77.8% and 81.8%, respectively. This study showed that in normal fetuses MCARI differs according to the behavioral state, and that resting phase MCARI is useful for predicting fetal distress in IUGR fetuses.

Doppler information pertaining to the intrapartum period

The aim of the study was to evaluate the use of color-Doppler velocimetry during the labor. 325 intrapartal measurements of the umbilical artery, fetal aorta, middle cerebral artery and arcuate arteries were performed in a group of 105 patients. The resistance index (RI) and pulsatility index (PI) were measured. During the active labor the RI and PI of the umbilical artery remained unchanged. The impedance in arcuate arteries have increased (p < 0.05). The RI and PI of the middle cerebral artery showed non significantly increased mean values when compared with the corresponding values during pregnancy. But, a short term, transitory decreased impedance is registered during the decrement slope of contraction. Since fetal outcome was normal in all newborns, these changes are considered as physiologic.

Doppler velocimetry of different sections of the fetal middle cerebral artery in relation to perinatal outcome

To assess the standard curves of pulsatility index (PI) in different segments of middle cerebral artery (MCA): initial segment (MI) and subcortical segment (M2); to determine the variation of the flow velocity waveforms (FVW) of the M1 and M2 segments of MCA in presence of fetal distress and to establish the possible correlation between the two segments of MCA. 50 normal pregnancies from 25 weeks of gestation to term and 20 pregnancy with alteration of fetal growth rate were investigated with serial records of the FVW of the M1 and M2 segments of the MCA and of the umbilical artery (UA) with a colour Doppler system. Severe fetal distress was associated to cerebral-placental ratio below 1 (C/P < 1). The perinatal outcome was established on the basis: 1) abnormal intrapartum CTG, 2) emergency cesarean section, 3) Apgar score at 1st and 5th minute after birth and 4) birth eight centiles. In normal pregnancy P1 of M2 was always higher than that of M1: therefore M2/M2 resulted below 1, with a maximum peak near 32 weeks of gestation. In presence of moderate fetal distress only P1 of M2 was reduced (M1/M2 > 1). It exists a significant difference of PI in M1 and M2 segments of fetal MCA during gestation: thus MCA so it is important to identify the tract of fetal MCA when recording its FVW. Moreover we suppose that an initial "cerebral sparing" effect exists in order to protect the cortex by the initial hypoxic injury: this is shown by a M1/M2 > 1. The progression of fetal distress results in a greater haemodynamic modification, the so called "brain sparing" which is usually present when C/P < 1.

[The relationship between blood flow redistribution in umbilical artery and middle cerebral artery and fetal growth in intrauterine growth retardation]

The aim of this study was to evaluate the usefulness of umbilical artery and middle cerebral artery PI and the ratio of these values as predictors of fetal growth-retardation and adverse perinatal outcome. In 100 normal fetuses and 105 intrauterine growth-retarded fetuses Doppler velocity waveforms were recorded from the umbilical artery and middle cerebral artery, and we calculated the incidence of low birth weight, gestational age at delivery, fetal distress and umbilical artery blood gas. The results were as follows: 1. There were moderate correlations between umbilical PI and birth weight (r = -0.43, p < 0.0001) and between middle cerebral artery PI and birth weight (r = 0.37, p < 0.0001) and a close correlation between cerebral-umbilical PI ratio and birth weight (r = 0.71, p < 0.0001). 2. There was a significant association between the cerebral-umbilical PI ratio and the HC/AC ratio (r = -0.46, p < 0.0001). 3. The cerebral-umbilical PI ratio was the best predictor of birth weight, fetal distress and neonatal mortality compared with umbilical artery PI and middle cerebral artery PI. In growth retarded fetuses, high umbilical artery PI and low middle cerebral artery PI, the so called "brain sparing effect" was demonstrated. The cerebral-umbilical PI ratio provided a better predictor of IUGR and adverse perinatal outcome than umbilical artery PI and middle cerebral artery PI alone.

Changes in blood flow velocity waveforms following fetal blood sampling

The umbilical artery, aorta, and middle cerebral artery pulsatility indices were investigated by pulsed Doppler ultrasound in 73 fetuses at 18-37 weeks of gestation, before and after fetal blood sampling performed either at the placental cord insertion (n = 46) or at the intrahepatic vein (n = 27). At the end of the procedure, after randomization, 35 fetuses were infused amounts of normal saline equal to the blood volume withdrawn, and 38 fetuses served as controls. Following blood sampling, the umbilical artery pulsatility indices decreased both in controls (p = 0.004) and in the saline group (p = 0.006). The middle cerebral artery velocity waveforms exhibited similar changes only in controls (p = 0.01), and no changes in fetal heart rate and aortic pulsatility indices were recorded in either group. The changes in blood flow velocity waveforms did not correlate with gestational age and the blood volume sampled, and were similar whether the site of sampling was the placental cord insertion or the intrahepatic vein. In 10 acidemic and/or hypoxemic fetuses, pulsatility indices in the umbilical and middle cerebral arteries were not modified by the blood sampling procedure. The release of vasoactive substances is most likely the cause of diminished vascular resistances following fetal blood sampling. Hypoxemic/acidemic fetuses may fail to mount a normal vasodilative response to needle puncture.

Nitric oxide and beta-adrenergic mechanisms modify contractile responses to norepinephrine in ovine fetal and newborn cerebral arteries

Ovine fetal cerebral arteries exhibit an enhanced contractile response to norepinephrine (NE) compared with newborns and adults. It is possible that beta-adrenergic receptors and/or nitric oxide (NO), a putative endothelium-dependent relaxing factor, differentially modulate cerebrovascular responsiveness to NE as a function of development. The present study evaluated the effect of the beta-adrenoceptor antagonist, propranolol, and the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (LNAME), on the contractile response of isolated middle cerebral artery (MCA) and basilar artery (BA) to NE during fetal development. MCAs isolated from four preterm fetal lambs (105 d of gestation), seven near-term fetal lambs (125-130 d of gestation), and eight newborn lambs (2-7 d of age) were evaluated using organ baths. BAs isolated from the near-term fetal and newborn lambs were also evaluated. Contractile reactivity of MCAs to NE decreased significantly during fetal maturation as manifested by a marked decrease in Fmax (maximal relative contractile force generated) and an increase in EC50 (Fmax = 100 +/- 7, 41 +/- 7, and 28 +/- 8% of KCl contraction; EC50 = 0.14 +/- 0.03, 1.09 +/- 0.36, and 1.07 +/- 0.22 microM for preterm fetus, near-term fetus, and newborn lamb MCAs, respectively, p < or = 0.05). Propranolol treatment (10(-5) M) increased Fmax (2-fold) only for newborn lamb MCAs. Pretreatment with LNAME (10(-4) M) markedly enhanced the contractile response to NE (7-fold decrease in EC50 and 2-fold increase in Fmax, p < 0.05) for near-term fetus MCAs, whereas preterm fetus and newborn lamb MCAs were unaffected by the inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

[Doppler ultrasound of the middle cerebral artery: pre-final normalization of cerebrovascular circulation?]

We report on the circulatory changes of a severely growth-retarded fetus at 26 weeks of gestation with intrauterine death after 6 days of observation and a birth weight of 480 g. On admission the fetus already showed signs of circulatory centralisation; furthermore, we found pulsation in the umbilical vein and diastolic reverse flow in the umbilical artery. During the days of observation this reverse flow increased and the compensatory phase of fetal circulatory centralisation was followed on the last day by a phase of circulatory decompensation with an apparently normal middle cerebral artery waveform, mimicking preterminal normalisation of fetal cerebral blood flow.