Experimental and clinical study on the blood supply of the subdermal vascular network island flap]

Vascular resistances of various fetal areas are assessed by Doppler ultrasound. The PI, RI and S/D indices are measured on the cerebral, renal, aortic and umbilical Doppler spectrum. Ratios of these indices based on the comparison of the cerebral (Rc) and the umbilical (Rp) resistances, or carotid (Rcc) and umbilical resistances, or cerebral (Rc) and aortic (Rao) resistances (Rc/Rp or Rp/Rcc, or Rc/Rao), measure the flow redistribution between the placenta and brain. The umbilical resistance indices, when greater than the upper limit of the normal range (> 2sd) are frequently associated with IUGR. (Sensitivity about 65 to 70%). Absent end diastolic flow is most of the time associated with severe IUGR and hypoxia and poor fetal outcome. A fairly good correlation was found between the existence of significantly decreased (< .2.sd) cerebral resistance and the development of post asphyxial encephalopathy in the neonate (Specificity 75% Sensitivity 87%). The earliest detectors of IUGR and hypoxia are the cerebral-umbilical cerebral-carotid, or cerebral-aortic ratios (Sensitivity 85% specificity 90%). When used as predictor of poor perinatal outcome in growth retarded fetuses, the cerebral umbilical ratio shows a sensitivity of 90% compared with 78% of the middle cerebral artery, and 83% for the umbilical artery indices. Changes of this ratio are well correlated with the fetal pO2 changes. The renal flow response to hypoxia depends on the degree of hypoxia. Opposite responses were found in case of moderate, and severe IUGR or hypoxia. Thus, it is too early to conclude if the renal indices are reliable parameters for the evaluation of fetal hypoxia. The sensitivity in predicting IUGR was for the aortic PI: 41% and for the aortic BFC (Blood flow classes): 57%. In predicting delivery for fetal distress, the corresponding values were 76 and 87%, respectively. Because the resistance indices are heart rate-dependent, it is dangerous to draw any conclusion from one single value of any of these parameters. Only several successive measurement of the Doppler indices or of their ratio, may lead to a reliable evaluation of fetal hemodynamics. In the case of significant IUGR with abnormal Doppler indices it is recommended to repeat the Doppler measurements daily both at the cerebral and umbilical or aortic level in order to follow up the fetal flow redistribution which is highly correlated with the fetal pO2 changes.     

Cardiac flow after fetal blood sampling in normally grown and growth-retarded fetuses

The objective of this study was to evaluate the effect of fetal blood sampling on cardiac flow velocity waveforms. Flow velocity waveforms were measured from the ascending aorta and pulmonary artery immediately before and after fetal blood sampling in 29 normally grown and 12 growth-retarded fetuses. The latter group was characterized by abnormal Doppler indices in the umbilical artery and middle cerebral artery suggestive of uteroplacental insufficiency as the causative factor of the impaired growth. The flow velocity parameters studied were the peak velocity, the time to peak velocity, and the left and right cardiac output and their ratio. In normally grown fetuses, the peak velocity and right and left cardiac output values increased significantly after fetal blood sampling, while no significant changes were observed in the other indices considered. The gestational age at the time of the procedure was positively related to the amplitude of these changes. In growth-retarded fetuses, fetal blood sampling did not induce any significant increase in cardiac output or peak velocities, while in more than 50 per cent of the fetuses these Doppler indices decreased. The amplitude of the decrease was significantly related to the severity of acidosis in the umbilical vein. In conclusion, the cardiac haemodynamic response to fetal blood sampling differs between normally grown and growth-retarded fetuses. This difference may explain the higher rate of complications occurring in the latter group of fetuses after blood sampling.     

Analysis of risk factors influencing imminent distress in growth-retarded fetuses undergoing oxygen test

We previously demonstrated a prognostic significance of maternal oxygen test in predicting imminent fetal distress. The purpose of this study was to investigate eventual other factors related to the length of the time interval elapsing between the Doppler diagnosis of brain sparing effect and abnormal fetal heart rate patterns. To this end we considered 101 growth-retarded fetuses free of structural and chromosomal abnormalities with a ratio between the pulsatility indices of umbilical and middle cerebral artery above the 95th centile in presence of a normal fetal heart rate pattern. The factors, other than the oxygen test, analyzed for a potential influence on this time interval were gestational age, presence of hypertension or preeclampsia, amniotic fluid index, severity of growth retardation (centile of the ultrasonographic estimated fetal weight) and 9 different Doppler indices calculated from extra- and intracardiac districts. Statistical actuarial methods were used to determine the effect of these prognostic factors on the duration of this time interval. The occurrence of abnormal fetal heart rate patterns (antepartum late heart rate decelerations) was used as censoring variable. The time interval between the entry in the study and delivery ranged from 1 to 39 days. Indications for delivery were fetal distress in 53 fetuses (52.4%) and different maternal or fetal complications in the remaining 48 fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mental illness in homeless women: an epidemiological study in Munich, Germany

This longitudinal observational study evaluates the stage at which coronary flow can be visualized by color-coded and pulsed wave Doppler sonography in fetuses with normal cardiac anatomy. Fetal biometry, echocardiography and Doppler examination of the umbilical and middle cerebral arteries, ductus venosus, inferior vena cava and umbilical vein were performed in 109 cases. Fetuses were divided into five groups based on the Doppler examination of the umbilical artery, birth weight and the ability to visualize coronary blood flow. Coronary blood flow was identified in six of 55 fetuses with normal growth who had normal Doppler studies and perinatal outcome. In these, visualization of coronary blood flow was possible after 31 weeks' gestation at a median gestational age of 37 weeks. Coronary blood flow was also visualized in ten of 54 fetuses with severe intrauterine growth retardation and highly pathological flow velocity waveforms in all vessels soon after a significant increase of venous indices in the inferior vena cava and ductus venosus. In these cases, coronary blood flow was identified at a significantly earlier gestational age (median 27 weeks). These fetuses had a poor perinatal outcome (average birth weight less than 3rd centile, mortality rate 50%, significantly lower umbilical artery blood pH and Apgar scores after 1 and 5 min). Intrauterine fetal death occurred in five fetuses after a median of 3.5 days following visualization of coronary blood flow. Median coronary peak blood flow velocities in the right coronary artery were higher in intrauterine growth-retarded than appropriate-for-gestational-age fetuses.     

Experimentally contaminated reabsorbable meshes: their evolution in abdominal wall defects

The effect of maternal hyperglycemia on fetal regional circulation in appropriate for gestational age and small for gestational age fetuses was evaluated. Color Doppler flow imaging and pulsed Doppler ultrasonographic assessments were made on 15 appropriate for gestational age and 19 small for gestational age fetuses, ranging from 33 to 40 weeks' gestation before, 60 minutes, and 120 minutes after a maternal 75 g glucose load. The pulsatility index (PI) was calculated for middle cerebral artery, descending aorta, splenic artery, renal artery, femoral artery, and umbilical artery. Simultaneously, maternal plasma glucose concentration was measured. Baseline PI value (1.50 +/- 0.31) for middle cerebral artery in small for gestational age fetuses was significantly lower than that (1.89 +/- 0.37) in appropriate for gestational age fetuses (p < 0.05); however, there were no significant differences in baseline PI values for other arteries in both groups. In appropriate for gestational age fetuses, the mean PI decreased from 1.89 +/- 0.37 to 1.47 +/- 0.33 at 60 minutes, and to 1.55 +/- 0.32 at 120 minutes (p < 0.05), but no changes were found in the other arteries. In small for gestational age fetuses, there was no significant change in PI value for each artery before and after maternal glucose load. Maternal hyperglycemia induces a significant decrease in cerebrovascular resistance in appropriate for gestational age fetuses but not in small for gestational age fetuses. These results provide a foundation for evaluating the effect of maternal hyperglycemia on fetal regional circulation.     

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.     

Intraobserver variability of pulsatility index measurements in three fetal vessels in the first trimester

PURPOSE: The intraobserver repeatability of pulsatility index measurements in 3 fetal vessels in the early weeks of gestation was evaluated. METHODS: The pulsatility index was calculated from the flow velocity waveforms from 3 fetal vessels in a series of 58 uneventful, low-risk, singleton first-trimester pregnancies using transvaginal color Doppler sonography. The intraobserver repeatability was expressed as the intraclass correlation coefficient. Mean menstrual age at the time of the examination was 10.3 weeks (range, 7.6-13). RESULTS: Flow velocity waveforms from the umbilical artery, abdominal aorta, and middle cerebral artery were obtained in 100% (58/58), 98.3% (57/58), and 100% (34/34) of cases, respectively. The intraclass correlation coefficients for these vessels were 0.89, 0.79, and 0.93, respectively. CONCLUSIONS: The intraobserver repeatability was acceptable for all the vessels studied.     

Doppler score for evaluating perinatal risk

Doppler sonography now has a definite place in the surveillance of risk pregnancies. Uniform clinical management is sometimes difficult especially in borderline cases. The following study demonstrates the possibility of standardizing and systematizing Doppler results using a score. In a collective of 253 pregnant women we performed Doppler examinations in the fetal aorta, umbilical artery, middle cerebral artery, internal carotid artery. The results were divided into 4 groups and correlated to the fetal outcome. There was a highly significant worsening in prognosis regarding duration of pregnancy, birth weight and rate of cesarean sections with increasing Doppler score. In the event of pathological and highly pathological scores, the average duration of pregnancy was 23 and 48 days shorter than normal. As a result, there was a highly significant reduction in the average birth weight compared to fetuses with normal Doppler scores: by 1060.7 g in the case of a pathological score and by 1633.5 g in the case of a highly pathological score. There was a highly significant correlation concerning the rate of cesarean sections and the indication "fetal distress". The average interval between diagnosis and birth was 6.3 days in the case of pathological Doppler findings and 2.3 days in the case of highly pathological findings. The difference was highly significant. In the case of highly pathological scores all fetuses were delivered after at least 5 days, compared with after at least more than 10 days in those with only pathological Doppler findings. This reflects the fact that there is none room for discretion in case of a highly pathological flow. In summary the Doppler score allows better estimation of fetal risk and can improve fetal prognosis by special monitoring and earlier obstetric intervention.     

The effects of nephrectomy on the developing fetus

Bilateral renal pathologies such as renal agenesis and renal dysplasia and lower urinary tract obstruction have been reported to result in pulmonary hypoplasia. Although oligohydramnios and resultant thoracic compression was suggested to be the cause of pulmonary hypoplasia, the exact mechanism is still unknown. Additionally the effect of absence of renal tissue on the development of the fetus has not been previously studied in detail. Therefore an experimental study was planned to investigate the effects of fetal nephrectomy on development. The fetuses from 27 New Zealand white rabbits were studied on the 23rd day of gestation. Right ovarian-end fetuses underwent bilateral nephrectomy or sham operations. Rabbits underwent hysterectomy on gestational day 30, and live fetuses were studied. Fetal body, lung, heart and liver weights, and lung, heart and thorax volumes were determined, organ weight/body weight ratios were calculated. Additionally, lungs were evaluated by histological examination. Although fetal nephrectomy resulted in decreased body weight (BW), lung, heart, liver weights and heart weight/BW ratio (p < 0.05), lung weight/BW and liver weight/BW ratios did not differ. Additionally, heart and thorax volumes were significantly decreased in the nephrectomy group (p < 0.05). However lung volume and thorax volume/BW ratio did not differ between groups. The histological evaluation of lungs revealed exfoliated cells but normal lung development. Bilateral fetal nephrectomy results in small-for-gestational age (SGA) status during birth without affecting the development of organic systems. Since SGA status may be associated with decreased placentofetal blood flow, bilateral nephrectomy may act through decreasing placentofetal blood flow and/or through the lack of kidney-related growth factors.     

Doppler ultrasonography of canine maternal and fetal arteries during normal gestation

Two-dimensional ultrasonography was used in combination with colour-flow imaging and pulsed wave Doppler ultrasonography to study the maternal circulation and the development of fetal vascularization in six Beagles during normal gestation. For the first time, the development of the circulation was demonstrated in the bitch and her fetuses intra vitam. The bloodstream was examined in small uteroplacental arteries, the umbilical artery, the fetal aorta and the common carotid artery. The duration of the study was from week 3 after insemination until birth. Relatively large vessels were detected by cross-sectional ultrasonography, and small vessels were detected by colour-flow imaging. In pulsed wave Doppler ultrasonography, the blood flow was measured and described using the parameters of systolic peak velocity, diastolic peak velocity, end-diastolic velocity, pulsatility index, resistance index, A:B ratio (systolic peak velocity:end-diastolic velocity) and S:D parameter (systolic peak velocity:diastolic peak velocity). The development of the measured parameters is typical and similar to that in humans. The systolic peak velocity of the canine maternal uteroplacental arteries shows important differences in comparison with humans. The pulsatility index, resistance index and A:B ratio decrease in nearly all vessels. Only the fetal common carotid artery has constant pulsatility and resistance indices during gestation. For the first time, the quality and quantity of the normal blood flow have been monitored during the whole of gestation. A normal circulation is fundamental for supplying the fetus adequately with oxygen and nutrients and thus for physiological development. These ultrasonographic results are the basis for further clinical studies.     

The renal arterial pedicle in the human fetus

To analyze the incidence of renal arteries variations during the fetal period and compare these findings with previous findings in adults, we studied the renal arterial pedicle in 70 human fetuses ranging in age from 13 to 36 weeks postconception. The fetuses were injected through the right common carotid artery with a red polyester resin to fill in the arterial tree enabling the identification and dissection of the small fetal arteries. The renal arteries were analyzed considering their number, origin, direction and site of penetration. Among the 70 fetuses studied, 30 (42.8%) presented at least one kidney with renal artery variations. In 6 fetuses the variation was bilateral. Among the total of 140 renal pedicles studied, 36 presented arterial variations (25.7%). We did not find statistically significant difference between right and left kidneys and between male and female fetuses. In the present study we did find kidneys with more than 2 arteries, probably because we did not study kidneys with any kind of development anomaly. Even kidneys with malrotations of the vertical axis were removed from the study.     

Prenatal ultrasonographic assessment of the middle cerebral artery: a review

Published reports, case studies, and articles regarding ultrasonographic morphology, physiology, and pathophysiology of the fetal middle cerebral artery obtained from a MEDLINE search from 1966 through January 1997 were reviewed. Both transabdominal and transvaginal color Doppler ultrasonographic modalities may be used to assess fetal middle cerebral artery flow hemodynamics. Altered middle cerebral artery flow velocities may be noted in various medical conditions that include various behavioral states, term and preterm labor, maternal medications (anesthesia, tocolytics), fetal compromise (growth restriction and hypoxia), twin-twin transfusion syndrome, invasive diagnostic procedures (amniocentesis and fetal blood sampling), fetal anemia and transfusion, in addition to intracranial fetal lesions (congenital anomalies and hemorrhage). In summary, knowledge of Doppler flow velocity of the fetal middle cerebral artery may assist prenatal diagnosis and management of complicated pregnancies.     

The response regulator-like protein Pos9/Skn7 of Saccharomyces cerevisiae is involved in oxidative stress resistance

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.     

Causality and control: key to the experiment

Maternal betamethasone administration causes a transient but considerable reduction in fetal body and breathing movements and in fetal heart rate variation. The aim of the present prospective study was to investigate whether there is evidence of circulatory changes in fetal, placental or uterine arteries, consistent with hypoxemia. Eighteen women at risk for preterm delivery received betamethasone to enhance fetal lung maturation. Doppler studies were performed before treatment, and 24 and 72 h after the second dose of betamethasone. Blood flow velocity waveforms were obtained from both uterine arteries, umbilical arteries, fetal descending aorta, fetal renal artery, and fetal cerebral arteries. No significant changes occurred in the pulsatility index of any of these blood vessels, suggesting that the transient reduction in fetal heart rate variation and fetal body and breathing movements following maternal betamethasone administration is not mediated through fetal hypoxemia.     

Effect of antenatal administration of thyrotrophin releasing hormone on fetal flow velocity waveforms

AIM: To determine whether antenatal administration of thyrotrophin releasing hormone (TRH), to promote lung maturation, alters blood flow through the fetal middle cerebral, umbilical artery, or ductus arteriosus and through the maternal uterine arteries. METHODS: The effect of transplacentally administered TRH on the fetal circulation was prospectively evaluated in 30 patients between 24 and 34 weeks' gestation. TRH (400 micrograms) was given to the mother intravenously either as a bolus or an infusion. Fetal effects were determined by measuring the maximum velocity and pulsatility index (PI) in middle cerebral artery, ductus arteriosus, uterine artery and umbilical artery Doppler waveforms. Measurements were made immediately before, and 10 and 60 minutes after maternal TRH administration. RESULTS: Intravenous injection of TRH had no significant effect on PI in the uterine, umbilical, or middle cerebral artery and the ductus arteriosus within 60 minutes of administration in either group. CONCLUSION: The antenatal use of TRH in conjunction with steroids for fetal lung maturity does not affect utero-placental or fetal haemodynamic variables, as measured by Doppler. These findings, therefore, do not support the suggestion that antenatal intravenous administration of TRH either as bolus or infusion may have immediate adverse vascular effects in the fetus.     

Changes in reactivity of the middle cerebral artery caused by cerebral circulation disturbances of ischemic and hemorrhagic types in rats

Reactivity of the middle cerebral artery (MCA) to serotonin was attenuated in vitro in vessels taken from rats following an audiogenic stress. The MCA reactivity to endothelin remained unchanged. Chronic cerebral ischemia diminished the 5-HT-induced contraction and the contractile responses to endothelin were enhanced. Preliminary hypoxic adaptation decreased the artery sensitivity to endothelin in ischemic animals. The findings suggest that a progressing ischemia may involve changes in reactivity of cerebral vessels whereupon hypoxic adaptation may prove to be protecting the brain from ischemia development.     

Cardiotocogram compared to Doppler investigation of the fetal circulation in the premature growth-retarded fetus: longitudinal observations

It was our objective to compare computerized fetal heart rate analysis with blood flow velocity waveform analysis of the arterial and venous fetal circulation in intrauterine growth retardation. We report five illustrative cases with longitudinal observations of fetal Doppler findings and fetal heart rate between 23 and 32 weeks of gestation. Blood flow waveforms were recorded from the umbilical artery, middle cerebral artery, descending aorta, ductus venosus and inferior vena cava. Fetal heart rate was analyzed by a computer system according to the Dawes-Redman criteria. The time sequence of deterioration is described individually for each fetus. An abrupt increase in pulsatility of ductus venosus waveforms with loss of forward flow velocity during atrial contraction preceded abnormally low short-term variation of fetal heart rate. With advanced gestational age and concomitant maternal disease, we observed severe alterations of flow velocity waveforms within 12 h of normal Doppler measurements, which is in contrast to findings in the second trimester, in which severely abnormal venous waveforms were observed over a period of several weeks before intrauterine death occurred. In a fetus with terminally low short-term variation, normal venous waveforms indicated fetal well-being despite an abnormal cardiotocogram (CTG). We challenge the current concept that the CTG is the best available parameter to determine the optimal time for elective delivery of premature growth-retarded fetuses. Deterioration in ductus venosus blood flow seems to precede an abnormal CTG and thus heralds the need for delivery.     

Doppler velocimetry determined redistribution of fetal blood flow: correlation with growth restriction in diamniotic monochorionic and dizygotic twins

OBJECTIVE: Our purpose was to study fetal growth and blood flow distribution in diamniotic monochorionic compared with dizygotic (diamniotic dichorionic) twins by use of Doppler velocimetry of the umbilical artery and middle cerebral artery. STUDY DESIGN: Study candidates were divided into group A, consisting of 33 pairs (66 fetuses) of diamniotic monochorionic twins, and group B, 50 pairs (100 fetuses) of diamniotic dichorionic twins. Diamniotic monochorionic placentation was confirmed by microscopic placental examination for group A. Diamniotic dichorionic placentation was ensured for group B by selecting only twins with different-sex pairs (dizygotic twins). Targeted ultrasonography with biometry was performed in each twin, and Doppler recordings of the umbilical artery and middle cerebral artery were obtained. Waveforms were analyzed and the systolic/diastolic ratio, the resistance index, and a measure of blood flow redistribution (brain-sparing effect), the cerebral/placental ratio, was calculated for each fetus. Growth status at birth was assessed by the number of small-for-gestational-age infants (< or = 10th percentile), low-birth-weight infants (< or = 25th percentile), and percent of growth discordance between twins. Intertwin differences were assessed by delta values (value of larger twin minus value of smaller twin). RESULTS: Diamniotic monochorionic compared with dizygotic twins demonstrated a significantly greater probability of blood flow redistribution. For the study population as a whole, the brain-sparing effect was noted in 67% of small-for-gestational-age babies and only 7% of non-small-for-gestational-age infants (p < or = 0.001). For the diamniotic monochorionic pregnancies blood flow redistribution occurred in 6 of 10 small-for-gestational-age infants (60%) and 6 of 46 non-small-for-gestational-age infants (13%). In the diamniotic monochorionic group small-for-gestational-age compared with non-small-for-gestational-age infants were more likely to show blood flow redistribution, which was the result of significantly decreased resistance in the middle cerebral artery and significantly increased resistance in the umbilical artery. Small-for-gestational-age infants (< or = 10th percentile) occurred much less frequently in the dizygotic group. Two of two small-for-gestational-age infants in the dizygotic group showed blood flow redistribution. Although the extremes of birth weight were more common in the diamniotic monochorionic group, both groups had relatively large numbers of small babies with birth weights in the lower 25th percentile (50.0% for diamniotic monochorionic and 44.0% for dizygotic twins, not significant). However, 42.3% (11/26) of diamniotic monochorionic twins who were in the low-birth-weight group showed blood flow redistribution compared with only 3.3% (1/30) whose birth weights were > or = 25th percentile (p < or = 0.001). In the dizygotic twins 10% of lower-birth-weight infants redistributed blood flow compared with 1% in the higher-birth-weight group, a nonsignificant difference. Diamniotic monochorionic compared with dizygotic twins were delivered earlier (32.9 weeks vs 34.8 weeks, p < or = 0.001), were smaller (1832 gm vs 2304 gm, p < or = 0.001), showed higher birth weight discordance (29.8% vs 14%, p < or = 0.05), and had greater numbers (19.7% vs 2.3%, p < or = 0.01) of infants at < or = 10th percentile birth weight. CONCLUSIONS: Diamniotic monochorionic twins from the lower-birth-weight groups more often show blood flow redistribution compared with dizygotic twins of similar low birth weights. Placental vascular connections and the attendant hemodynamic changes in the fetuses of diamniotic monochorionic twins probably account for this difference. Brain-sparing events occur commonly without clinical twin transfusion syndrome in this group. These findings have implications for management.     

A comparative study of velocity measurements in major blood vessels using magnetic resonance imaging and Doppler ultrasound

Velocity measurements in major blood vessels were obtained in studies of volunteers using magnetic resonance imaging (MRI) and compared with Doppler ultrasound (US). The vessels studied were the abdominal aorta, superior mesenteric artery, common carotid artery, superficial femoral artery and middle cerebral artery. Using a paired t-test, no significant difference was found between velocity values estimated by MRI and US (p > 0.08). The relative advantages of each technique in radiological practice are discussed.     

Doppler examination of cerebral arteries in uremic children

Transcranial Doppler ultrasonography is a useful method for the estimation and monitoring of cerebral circulation in dialyzed patients. The aim of this study was to evaluate the effect of disease and treatment on cerebral circulation in children on maintenance hemodialysis (HD) and children prior to renal replacement therapy. We demonstrated that in uremic children blood flow velocities of the internal carotid artery (ICA), anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA) 120 min and 240 min from the beginning of an HD session were significantly lower than values immediately before HD. Changes in blood flow velocities of MCA and ACA during HD correlated significantly with changes in mean arterial pressure during HD. There was no correlation between changes in blood flow velocities and intradialytic changes in hematocrit values, ultrafiltration, hemoglobin concentration, and blood urea nitrogen values. Mean blood flow velocities of ICA, MCA, and PCA in euvolemic children on conservative treatment were significantly higher than after a HD session in children on maintenance HD. The factors responsible for intradialytic velocity changes of cerebral arteries in uremic children require further examination.