Fetal central blood circulation in the third trimester of normal pregnancy--a longitudinal study. II. Aortic blood velocity waveform

Cardiovascular function in adulthood following intrauterine growth restriction with abnormal fetal blood flow

OBJECTIVES

To examine whether intrauterine growth restriction (IUGR) is associated with increased cardiovascular risk later in life.

METHODS

We examined 19 young adults (aged 22-25 years) who were born at term after IUGR, along with 18 controls. All had been examined previously with fetal Doppler, and in the present follow-up with echocardiography, carotid echo-tracking ultrasound, applanation tonometry, blood pressure and laser Doppler, in order to characterize their cardiac and vascular geometry and/or function.

RESULTS

The diameter of the ascending aorta and the left ventricular diameter were smaller in the IUGR group, but only ascending aortic diameter remained significantly smaller after adjustment for body surface area (P < 0.05). The aortic pressure augmentation index was higher in the IUGR group (P < 0.05). The common carotid artery diameter, intima-media thickness and distensibility as well as left ventricular mass and function were similar in the two groups. IUGR status was found to be an independent predictor of ascending aortic diameter.

CONCLUSIONS

IUGR due to placental dysfunction seems to contribute to the higher systolic blood pressure augmentation and the smaller aortic dimensions that are observed in adults more than 20 years later, with possible negative consequences for future left ventricular performance due to increased aortic impedance.

Cognitive function in young adults following intrauterine growth restriction with abnormal fetal aortic blood flow

OBJECTIVE

Intrauterine growth restriction (IUGR) is a recognized risk factor for neurological deficits later in life. Abnormal fetal blood flow in the presence of IUGR helps to distinguish fetuses with true growth impairment from those that are small but normally grown. This study aimed to evaluate the influence of IUGR with abnormal fetal blood flow on cognitive function and psychological development in young adults.

METHODS

Cognitive capacity (Wechsler adult intelligence scale-III (WAIS-III)) and psychological development (symptom check-list and Wender Utah rating scale) were evaluated at 18 years of age in 19 subjects who had had IUGR (abnormal fetal blood flow in the descending aorta and birth weight small-for-gestational age) and in 23 control subjects who had had normal fetal aortic blood flow and birth weight appropriate-for-gestational age (AGA). School grades at 16 years of age were also recorded.

RESULTS

The IUGR subjects had significantly lower results at 18 years of age in the combined subtests of the WAIS-III measuring executive cognitive functions (P = 0.03) and lower school grades at 16 years of age (P = 0.03) compared with the AGA group. IUGR subjects did not exhibit significantly more psychological distress symptoms.

CONCLUSION

IUGR with abnormal fetal blood flow is associated with impaired executive cognitive function in young adults.

Hemodynamic evaluation of a prenatal thoracoamniotic shunt for fetal pleural effusion

AIMS

To evaluate the efficacy of a thoracoamniotic shunt for the treatment of pleural effusion (PE) in the view of hemodynamics.

METHODS

The preload index (PLI) in the inferior vena cava (IVC), the maximal flow velocity of the descending aorta (VAomax), skin edema on the thorax and the ratio of lung to the thorax transverse area (L/T) as measured by ultrasound were evaluated before and after thoracoamniotic shunt placement for 5 fetuses with PE.

RESULTS

The PLI and skin edema on the thorax decreased significantly after shunt placement compared to before shunt placement (PLI before: 0.488 +/- 0.036, after: 0.348 +/- 0.043, P < 0.05; edema before: 15.3 +/- 2.06 mm, after: 9.00 +/- 0.63 mm, P < 0.05). Furthermore, the L/T increased significantly after shunt placement compared to before (before: 0.220 +/- 0.013, after: 0.260 +/- 0.011, P < 0.01). No significant difference in VAomax was seen between before and after shunt placement (before: 101.5 +/ -6.39 cm/s, after: 10.7.6 +/ -5.41 cm/s, P = 0.16).

CONCLUSIONS

The shunt for PE improved PLI especially in the fetal hemodynamics significantly.

Impaired vascular growth in late adolescence after intrauterine growth restriction

BACKGROUND

Abnormal blood flow in a fetus small for gestational age indicates true fetal intrauterine growth restriction (IUGR). We tested the hypothesis that IUGR with abnormal fetal blood flow is associated with long-term abnormal vascular morphology and function in adolescence.

METHODS AND RESULTS

In a prospective study, vascular mechanical properties of the common carotid artery (CCA), abdominal aorta, and popliteal artery (PA) were assessed by echo-tracking sonography in 21 adolescents with IUGR and abnormal fetal aortic blood flow and in 23 adolescents with normal fetal growth and normal fetal aortic blood flow. Endothelium-dependent and -independent vasodilatation of the brachial artery was measured by high-resolution ultrasound. After adjustment for body surface area and sex, the IUGR group had significantly smaller end-diastolic vessel diameters than the referents in the abdominal aorta and PA (mean difference, 1.7 mm [95% CI, 0.62 to 2.74] and 0.6 mm [95% CI, 0.25 to 1.02], respectively) (P=0.003 and P=0.002, respectively), with a similar trend in the CCA (P=0.09). A higher resting heart rate was observed in the IUGR group (P=0.01). No differences were found in stiffness or in endothelium-dependent and -independent vasodilatation between the 2 groups.

CONCLUSIONS

IUGR caused by placental insufficiency appears to be associated with impaired vascular growth persisting into young adulthood in both men and women. The smaller aortic dimensions and the higher resting heart rate seen in adolescents with previous IUGR may be of importance for future cardiovascular health.

Visual function in young adults following intrauterine growth retardation

BACKGROUND

Intrauterine growth retardation (IUGR) resulting in infants born small for gestational age is a known risk factor for neurologic deficits and may predispose to poor cognitive development later in life. We recently found an association between IUGR and a reduced neuroretinal rim area at 18 years of age. We evaluated the possible association between IUGR and visual function.

SUBJECTS AND METHODS

We studied 26 subjects who had been born small for gestational age and 20 subjects whose birth weights were appropriate for gestational age (controls) using letter acuity thresholds, color vision testing, full-threshold frequency doubling technology perimetry, and rarebit perimetry at 18 years of age. gestational age had a rarebit hit rate below the normal range as compared with none of the controls (P = .006). These 8 subjects had a significantly smaller rim-disc ratio compared with the subjects who were small for gestational age who had a normal rarebit hit rate (P = .047). The frequency doubling technology indices did not differ significantly between the control group and the group that was small for gestational age, nor did the visual acuity, refraction, and color vision test results.

CONCLUSION

These data indicate that IUGR is associated with an increased rate of impaired visual function, which can be detected by using rarebit perimetry but not frequency doubling technology perimetry, visual acuity, or color vision tests.

Abnormal retinal optic nerve morphology in young adults after intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a recognized risk factor for neurologic deficits later in life. Abnormal fetal blood flow in the presence of fetal growth retardation helps to distinguish true fetal growth impairment from small but normally grown infants. The present study aimed to investigate the influence of IUGR with abnormal fetal blood flow on retinal optic nerve morphology at 18 y of age. A prospective study was performed in 19 subjects with IUGR [abnormal fetal aortic blood flow velocity; median birth weight deviation of -31% (-22 to -42%; median (range)] and in 23 subjects with a normal birth weight for gestational age [normal fetal aortic blood flow velocity; median birth weight deviation of -2% (-10 to 22%)]. All subjects were previously examined concerning minor neurologic dysfunction (MND) at 7 y of age. The ocular fundus was examined by ophthalmoscopy, and the optic nerve morphology was evaluated by digital image analysis. Decrease in neuroretinal rim area at 18 y of age was associated with increasing negative birth weight deviation (r = 0.71, p < 0.0001). The subjects with severe MND at 7 y had a reduced neuroretinal rim area [median (range), 1.57 mm(2) (1.37-1.78 mm(2))] compared with those with less severe MND [1.94 mm(2) (1.33-2.71 mm(2))] and with those with normal neurologic function [2.18 mm(2) (1.75-2.70 mm(2)); p < 0.05 and p < 0.0001, respectively]. A decrease in neuroretinal rim area reflects either a reduction in axonal volume or a decrease in the number of axons in the optic nerve. It is yet unclear whether this finding represents neuronal changes within other cerebral regions in subjects with IUGR.

Abnormal retinal vascular morphology in young adults following intrauterine growth restriction

OBJECTIVE

Intrauterine growth restriction (IUGR) resulting in low birth weight for gestational age may predispose one to development of cardiovascular disease later in life. Abnormal fetal blood flow in the presence of fetal growth restriction helps to distinguish infants with true fetal growth impairment from small but normal infants. Our goal was to investigate associations between IUGR with abnormal fetal blood flow and abnormal retinal vascular morphology at 18 years of age.

METHODS

A prospective study was performed with 21 subjects with IUGR (abnormal fetal aortic blood flow velocity; birth weight small for gestational age; median birth weight deviation from the population mean of -31% [range: -22% to -42%] and in 23 subjects with birth weight appropriate for gestational age [normal fetal aortic blood flow velocity; median birth weight deviation of -2% (range: -10% to 22%)]). The retinal vessel morphology was evaluated by digital image analysis.

RESULT

Subjects with IUGR (n = 21) had significantly less retinal vascularization as evidenced by a lower number of vascular branching points (median: 26; range: 20-31) as compared with the subjects who were born appropriate for gestational age (median: 28; range: 26-32). Within the entire group (N = 44), increasing negative birth weight deviation was associated with a reduced number of vascular branching points (r = 0.36.

CONCLUSION

Our findings show that IUGR with abnormal fetal blood flow is associated with abnormal retinal vascular morphology in young adult life.

A longitudinal analysis of arterial dopler parameters in growth restricted fetuses

Doppler parameters enable noninvasive and direct detection of placental insufficiency and brain sparing effect, which occurs as an adaptive mechanism to chronic hypoxemia. It is of great interest if further changes of Doppler parameters, which occur after the detection of the first pathologic value, can anticipate a moment of fetal distress. We investigated growth-restricted fetuses with the brain sparing effect in the time interval between the detection of blood flow redistribution until the distress. The aim of our study was to evaluate longitudinally Doppler parameters in umbilical (Aum), medial cerebral (MCA), renal (AR) and femoral (AF) artery and find: 1) if there are significant changes in their value; 2) the character and time interval of these changes; and 3) if they differ from changes in biophysical profile (BFP). MATERIALS AND METHODS Prospective clinical study evaluated 35 pregnancies with fetal growth restriction. Fetuses were selected for the study if: 1) there were pathologic cerebral/umbilical (C/U) ratio, 2) at least four Doppler examinations in 3-4 days interval were performed and 3) prepartal fetal distress, defined as silent fetal heart rate pattern with spontaneous and late decelerations, was present. In 28 neonates after delivery umbilical artery gas and acid-base status was determined. Blood flow velocity waveforms were evaluated in Aum MCA, AR, and AF. Arterial blood flow was estimated by pulsatility index (Pi), while in Aum we also used: present end-diastolic velocity (PEDV) absent end-diastolic velocity (AEDV) and reverse end-diastolic velocity (REDV). All of the fetuses were monitored by cardiotocogram (CTG) once to twice a day and by BFP twice a week. Elective Cesarean section was done in the presence of distress, except if severe immaturity or extreme malnutrition occurred. RESULTS Etiological factors of placental insufficiency were: 1) hypertensive syndrome (n=26), 2) chronic renal disease (n=3), 3) primary antiphospholipid syndrome (n=2), 4) diabetes mellitus (n=1), 5) cardiac disease (n=1) and 6) unknown (n=2). Initial Doppler examination, with the detection of pathological C/U, was done in time interval between 26. to 32. weeks of gestation (wg) (29.4 ? 2.5) delivery was between 29. to 34. wg (32.2 ? 1.9); and average body weight was 1327 ? 245g. Pathological BFP was registered in 91.4% of fetuses. Cesarian section has not been done, in spite of distress, in two fetuses (5.7%) due to their extreme immaturity and/or malnutrition, so they died "in utero". Hypoxemia was registered in 96.4% (27/28) neonates, while acidosis in 71.4% (20/28). Neonatal morbidity was 93.9% (31/33), neonatal mortality 8.6% while perinatal mortality was 14.3%. We found high significant difference (P<0.001) in Pi Aum, Pi ACM and Pi AR in the time interval between the detection of pathological C/U ratio and fetal distress, while the difference was insignificant for the values of Pi AF (table). The value changes are characterized by: continuing increase of Pi Aum, with a maximum in the last week before the distress; biphasic character of PI MCA - tendency to decrease in the first two and significant increase in the last week; and significant increase of Pi AR one and a half week before the distress (table, graphic). Three weeks before the distress in 7 (53.8%) cases we registered PEDV, in 6 (46.2%) AEDV, while we didn`t register REDV in any case. In the last week there were 3 (8.6%) PEDV, 23 (65.7%) AEDV and 9 (25.7%) REDV.. DISSCUSSION Significant changes in Doppler parameters suggest that even after the blood redistribution in growth restricted hypoxemic fetuses further haemodynamic changes occur. Preterminal increase in Pi Aum can be due to: 1) release of leucotrien, tromboxan and free oxygen radicals and consecutive vasoconstriction in villous arteries; 2) increase of diastolic arterial pressure as a result of hypoxic-ishemic central nervous system (CNS) insult; 3) decreased combined heart minute volume in preterminal phase of hypoxemia. The increase of Pi MCA values is a result of hypoxic-ishemic CNS insult. As a consequence of hypoxia ischemia occurs by two mechanisms: local vasodilatatory agents production decrease, or due to the brain edema. The increase of Pi AR values can be explained by severe hypoxemia with the failure of local autoregulation of renal blood flow. The greatest changes in BFP values were registered in the first half, while in Doppler parameters in the second half of the studied interval suggesting that Doppler parameters more accurately announce fetal distress. We can conclude the following: 1) fetal distress appears after the presence hypoxic-ischemic CNS insult, and therefore late when sequels are concerned; 2) if the fetus is mature, elective delivery should be planed after the appearance of pathological C/U ratio, or with the pathological BFP at the latest, in order to avoid post-hypoxic sequels; 3) if the fetus is immature, pregnancy can be prolonged safely, in spite of pathological C/U ratio and BFP, with intensive monitoring of Doppler parameters until the detection of their increased values.

A transfer function-based mathematical model of the fetal-placental circulation

The circulation of a human fetus has been modeled using a transfer function that is based on the arterial dimensions at 28 weeks gestational age (GA). These dimensions have then been adapted for growth between 28 and 40 weeks GA. The input to the model is a series of current pulses at the fetal heart rate, where current in the model is analogous to volume blood flow in the fetus. The arterial system is divided into short segments that are cascaded together. The respective transfer functions are based on the dimensions, wall properties and fluid characteristics at each frequency and GA. Bleed off conductances distribute current to circuits representing the various anatomical regions. In particular, the placenta is simplified to a symmetrically distributed network of branching vessels, each represented by a transfer function. All calculations are performed in the frequency domain, after which the inverse Fourier transform is used to calculate the currents that represent the time-domain blood flow waveforms. Simulated flow waveform resistance index and pulsatility index values are within 8% of those reported for human clinical studies, at all gestational ages.

A transmission line model of the human foetal circulatory system

A transmission line model of the human foetal circulatory system is presented. The model has been developed in the frequency domain with the cardiac input modeled as a flow rather than as a pressure pulse and is structured upon electrical transmission line analogies. The model is formed by cascading solutions to the two-dimensional Navier-Stokes equations for both oscillatory and steady, laminar viscous fluid flow in isotropic visco-elastic tubes with thick walls, which are constrained by surrounding tissues. Simulations allow for representation of both forward and retrograde travelling flow and pressure waves in all of the main foetal arterial vessels. The solution is verified by a comparison of model generated Doppler indices in the thoracic aorta, abdominal aorta, iliac artery and both ends of the umbilical arteries with previously published indices obtained by clinical measurements in these arteries. For simulations of blood flow in a healthy foetus, the model generated Pulsatility and Resistance indices were on average within 8% of the corresponding clinical measurements. The model results also demonstrates that placental resistance must increase by a factor of three, corresponding to a 60% decrease in flow to the placenta, before umbilical arterial absent end diastolic flow is observed. Differences between indices obtained from simulations at opposite ends of the umbilical arteries increase with increasing placental resistance.

Systemic assessment of fetal hemodynamics by Doppler ultrasound

The aim of our study was to investigate the parameters of fetal circulation of normal pregnancies and their relationship to fetal cardiac output. We performed a cross-sectional study of 315 normal singleton pregnancies between 20 and 40 weeks' gestation without fetal chromosomal or structural malformations. After follow-up to delivery, 212 patients who fit all the criteria were enrolled for final analysis. Blood flow velocity waveforms were obtained from the tricuspid and mitral ventricular inflow, ascending aorta (AAO), pulmonary artery (PA), middle cerebral artery (MCA), renal artery (RA), umbilical artery (UA), descending aorta (DAO), inferior vena cava (IVC) and ductus venosus (DV) using duplex (real-time Doppler) ultrasound (US) scanner. The peak velocity of DV, AAO, PA and MCA were also obtained. At the intracardiac level, the ratio of peak flow velocity of E wave to peak flow velocity of A wave (E:A ratio) of mitral valve (MV) increased more rapidly than tricuspid valve (TV) E:A ratio. For the great vessels, aortic peak velocity remained higher than the pulmonary peak velocity with advancing gestation. The cardiac output closely correlated to the cardiac compliance and flow resistance indices at arterial and venous level. The acceleration time in the fetal arteries increased with advancing gestation in AAO, PA, MCA and DAO, but it decreased in RA and kept constant in UA. In addition, the acceleration time of UA was unrelated to cardiac output. The changes of the fetal intracardiac, arterial and venous impedances were remarkable through the gestation and related to cardiac output. Fetal cardiac output correlated well with the changes of arterial resistance, except with the DAO. The ventricular compliance increased with advancing gestation, especially in the left side, and was highly related to the change of cardiac output. The acceleration time in major arteries positively correlated with the gestational age and cardiac output, except in UA and RA; this indicates the difference of the changes of mean arterial pressure in uteroplacental circulation, fetal organs and great vessels. In conclusion, the fetal cardiac output correlated well with the ventricular compliance and was influenced by both hemodynamic changes in peripheral resistance and mean arterial pressure.

Association between a low umbilical artery pulsatility index and fetal distress in labor in very prolonged pregnancies

OBJECTIVE

To investigate the association between fetal, umbilical and uterine circulatory changes and adverse perinatal findings in very prolonged pregnancies.

STUDY DESIGN

44 women proceeding to 43 completed weeks of gestation with the intention of a trial of vaginal delivery were studied prospectively with ultrasound Doppler velocimetry. An intensified fetal surveillance was routinely commenced at 42 weeks and only uncomplicated pregnancies were allowed to proceed. The endpoint perinatal measures were oligohydramnios, fetal meconium release, fetal distress in labor and birth asphyxia. Flow variables in different groups were compared with the Mann-Whitney U test, Student's unpaired t-test, Wilcoxon signed-rank matched-pairs test, Fisher's exact test and contingency table analysis, and a two-tailed P value <0.05 was considered statistically significant.

RESULTS

The umbilical artery pulsatility index was significantly lower in cases of fetal meconium release (n=12) and fetal distress (n=7). The umbilical venous flow velocity was significantly lower in cases of meconium, and the fetal aortic volume flow significantly higher in cases of fetal distress. No significant flow changes were found in connection with oligohydramnios (n=5) and birth asphyxia (n=2). Uterine flow was not significantly affected in any group.

CONCLUSIONS

In very prolonged pregnancies, fetal distress in labor was not associated with an increased placental vascular resistance. In contrast to previous reports, the umbilical artery pulsatility index was low in cases of fetal distress and meconium release. The etiology is unknown, but a subclinical fetal hypoxia might have triggered a vasodilation of placental vessels. Vasodilation at an unchanged volume flow could also explain the decrease of umbilical venous flow velocity. The increased aortic volume flow indicates an increase of cardiac output in fetuses later developing distress in labor.

Fetal and uteroplacental circulatory changes in pregnancies proceeding beyond 43 weeks

BACKGROUND

Practically all reference curves for Doppler blood flow variables in pregnancy end at 40 weeks.

OBJECTIVE

To study fetal and uteroplacental circulatory changes in pregnancies proceeding beyond 43 weeks.

STUDY DESIGN

Longitudinal comparisons from 42 to 43 weeks and comparisons with controls at term.

MATERIAL

Thirty-four women delivered after 43 completed weeks (301 days) and a control group of 32 women delivered at 271 days of gestation.

METHODS

From 42 weeks (294 days), serial Doppler blood flow measurements were performed in the fetal descending aorta, umbilical vessels, and maternal uterine artery.

STATISTICAL METHODS

Student's unpaired t-test, Mann-Whitney U-test, and Fisher's exact test for comparison of groups; Student's paired t-test and Wilcoxon's signed-rank matched-pairs test for longitudinal data; simple linear regression analysis for comparison of variables. A two-tailed P-value of < 0.05 was considered statistically significant.

RESULTS

From 42 to 43 weeks, the mean flow velocity decreased significantly in the fetal aorta and increased significantly in the umbilical vein. Compared to controls, the velocity and volume flow in the aorta and the umbilical artery flow resistance were significantly lower at 43 weeks. No significant change in uterine artery flow resistance was found.

CONCLUSIONS

The changes in Doppler blood flow variables were all in accordance with physiological circulatory alterations enhancing continued fetal growth until the late post-term period. There were no signs of any general circulatory deterioration. Doppler velocimetry reference values at term may not be appropriate for evaluation of very advanced gestations.

Randomised controlled trial of methyldopa and isradipine in preeclampsia--effects on uteroplacental and fetal hemodynamics

This is a prospective randomised controlled study in 21 women admitted with preeclampsia in the third trimester. The mean arterial blood pressure decreased by 11.1 mmHg (95% confidence interval -14.9 to -7.3 mmHg) in the methyldopa group, and by 9.3 mmHG (95% confidence interval-14.4 to -4.2 mmHG) in the isradipine group. The maternal heart rate decreased by 6.9 beats per min (95% confidence interval -11.6 to -2.2 bpm) during methyldopa treatment, and by 2.5 beats per min (95% confidence interval -9.2 to 4.3) during isradipine treatment. Pulsatility index in maternal and fetal vessels was not affected by either of the two drugs. The birth weight and placental weight and neonatal outcome were similar and uneventful. The hypotensive effect was similar for methyldopa and isradipine. Except reduced maternal heart rate on methyldopa, fetal and uteroplacental hemodynamics were not altered during treatment of preeclampsia with methyldopa or isradipine.

Acceleration time in normal fetal umbilical artery at term and its relationship to the cord blood hematocrit

The purpose of this study was to test the hypothesis that the acceleration time (AT) of the fetal umbilical artery remains constant at term for normal pregnancies. In addition, we also examined whether the AT has any correlation with umbilical cord blood hematocrit (Hct). In total, 539 normal-term fetuses with menstrual ages (MA) ranging from 37 weeks to 42 weeks were enrolled in a cross-sectional design. The AT of the fetal umbilical artery was measured prior to delivery using a high-resolution, real-time Doppler scanner. All were delivered within 2 days of the ultrasound examination. At parturition, blood from the umbilical vein was collected and the red cell indices, including the Hct, were determined. The results indicated that the mean values of AT of the umbilical artery remained constant during normal-term pregnancies from 37 weeks to 42 weeks, menstrual age (mean: 0.104 sec, SE: 0.001 sec, n = 539). Although the AT was thought to be affected by the Hct, the AT had no correlation with umbilical venous Hct (n = 539, r = 0.002, p > 0.05). This constant value of the AT may be used as a reference for fetal physiology and perinatal medicine.

Input impedance of the lower abdominal aorta in chronically instrumented fetal sheep

Five fetal sheep (gestational age, 118 to 125 days) were instrumented to measure impedances of the lower abdominal aorta. Four days after surgery, flow and pressure pulses were recorded during control conditions and during infusion of norepinephrine (0.3 to 3 micrograms.min-1.kg-1 body weight) or angiotensin II (0.2 to 3 micrograms.min-1.kg-1). The protocol was repeated after injection of hexamethonium (10 mg.kg-1). Moduli and phases of impedances for the first ten harmonics were calculated by fast Fourier transformation. During control, input resistance was 4300 +/- 940 dyne.s.cm-5 (mean +/- SD) at a mean blood flow of 13.3 +/- 2.4 cm3.s-1 and pressure of 54,960 +/- 6980 dyne.cm-2. Moduli fell to 50% of input resistance between 2 and 3 Hz and, declining continuously, reached a minimum of 20% near 10 to 12 Hz, then increased slightly to 30% at about 30 Hz. At the first three harmonics, flow was always leading pressure. Infusion of angiotensin or norepinephrine increased impedance moduli significantly. Resistance increase was largest with angiotensin (19,800 +/- 11,370 dyne.s.cm-5), but no difference was detectable between angiotensin and norepinephrine when related to the same increase of input resistance. The position of the minimum seemed to be unchanged at high resistance values, but relative impedance moduli were smaller than during control, and low-frequency phases were significantly more negative. An analog of inertance, compliance, and resistance to steady flow was used to simulate impedances, and the effect of resistance increases on flow waveforms in the fetal abdominal aorta was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of methyldopa on uteroplacental and fetal hemodynamics in pregnancy-induced hypertension

OBJECTIVE

Our purpose was to study the effect of methyldopa on uteroplacental and fetal hemodynamics in women with pregnancy-induced hypertension.

STUDY DESIGN

A prospective study of Doppler ultrasonographic blood flow data before and after 1 week of methyldopa treatment was conducted at the Department of Obstetrics and Gynecology, National University Hospital, Singapore, in 20 women (mean 35 weeks' gestation) with pregnancy-induced hypertension. The main outcome measures were maternal blood pressure, maternal and fetal heart rate, and blood velocity waveforms characterized by the pulsatility index in the fetal ascending aorta, middle cerebral artery, umbilical artery, and maternal uterine and arcuate arteries. Statistical evaluation was performed with t tests for paired observations.

RESULTS

Maternal mean arterial blood pressure was reduced 9.7 mm Hg (95% confidence interval -13.8 to -5.6), and mean heart rate decreased 6.3 beats/min (95% confidence interval -11.1 to -1.4). Mean pulsatility index in the uterine (0.93 to 0.92) and arcuate arteries (0.61 to 0.73) were unchanged after treatment. Fetal hemodynamic changes before and after treatment were not significant. Fetal and neonatal outcome was uneventful.

CONCLUSION

Short-term treatment with methyldopa in the last trimester in women with pregnancy-induced hypertension reduced maternal blood pressure and heart rate but had no adverse effects on uteroplacental and fetal hemodynamics.

Blood flow velocity in the fetal abdominal aorta and in the umbilical artery in uncomplicated pregnancies

The blood flow velocity waveform (BFWV) in fetal vessels depends on the stroke volume and the frequency of the fetal heart, the compliance of the vessel and the peripheral resistance of the fetal vascular bed. The objective of the present study was to establish the change of the BFVW throughout gestation and whether the change of the resistance indices are related to the peak flow velocity and/or the end-diastolic flow velocity. The BFVW of the fetal abdominal aorta and of the umbilical artery at 27th-30th week and at 37th-40th week of gestation were analysed in fifteen patients with uncomplicated pregnancies and subsequent normal outcome. The measurement was performed with a pulsed duplex scanner (Kranzbühler). The Doppler beam had a fixed angle of 50 degrees to the fetal vessel in all cases. The peak flow velocity in the fetal aorta remained constant from the 27th-30th week to the 37th-40th week of gestation: 1418 +/- 248 Hz vs. 1448 +/- 269 Hz. The end-diastolic flow, however, showed a significant increase during the respective periods: from 270 +/- 59 Hz to 325 +/- 69 Hz. The peak flow velocity in the umbilical artery was about 25% below that of the fetal aorta: 1028 +/- 149 Hz (27th-30th week) and 1106 +/- 196 Hz (37th-40th week). The end-diastolic flow, however, increased by about 41%: 292 +/- 86 Hz vs. 412 +/- 83 Hz demonstrating a tremendous change of the compliance and the peripheral resistance in the umbilical vascular system. These alterations are also exhibited by the resistance indices. The resistance indices S/D, PI and RI of both vessels were related to the EDF of the abdominal aorta and the umbilical artery at the respective gestational age. It demonstrated that the EDF is of major influence on the calculated resistance indices. The blood flow in the aorta and the umbilical artery was 135(+/- 18) ml/kg/min and 143 (+/- 21) ml/kg/min, respectively. In conclusion, the BFVW for fetal surveillance should be measured under a constant angle in the fetal abdominal aorta. It gives a good information concerning the peripheral resistance and compliance in the respective vascular areas. The EDFV has its lowest value at 200 Hz in the fetal aorta and in the umbilical artery under physiological conditions.

Randomised controlled trial of atenolol and pindolol in human pregnancy: effects on fetal haemodynamics

OBJECTIVE

To compare the effects of uteroplacental circulation of two beta adrenoceptor blockers, atenolol (cardioselective) and pindolol (non-selective with intrinsic sympathomimetic activity).

DESIGN

Controlled double blind double dummy study.

SETTING

Departments of obstetrics and gynaecology in two Swedish university hospitals.

SUBJECTS

29 women with pregnancy induced hypertension in the third trimester, 13 randomised to atenolol and 16 to pindolol.

MAIN OUTCOME MEASURES

Pulsatility index in fetal aorta, umbilical artery, and maternal arcuate artery. Volumetric blood flow in fetal aorta and umbilical vein.

RESULTS

Mean arterial blood pressure decreased by 9.0 (95% confidence interval -13.0 to -5.0) mm Hg in the atenolol group and by 7.8 (-11.4 to -4.2) mm Hg in the pindolol group. During atenolol treatment the pulsatility index increased significantly from 1.82 (SD 0.20) to 2.07 (0.32) in the fetal thoracic descending aorta, from 1.44 (0.28) to 1.79 (0.27) in the abdominal aorta, and from 0.93 (0.17) to 1.05 (0.19) in the umbilical artery; the volumetric blood flow in the umbilical vein decreased from 106 (28.8) to 84 (22.6) ml/min/kg. No such changes were seen after treatment with pindolol. Birth weight was similar in the two groups but placental weight was significantly different (529 (122) g in atenolol group v 653 (136) g in pindolol group; p = 0.03).

CONCLUSION

The hypotensive effect was similar with both drugs, but only the beta 1 blocker atenolol had significant effects on fetal haemodynamics, although within normal ranges. The implications of these findings can be only speculative, but negative fetal consequences of beta 1 adrenoceptor blockade cannot be excluded.

The current status of maternal and fetal blood flow velocimetry

Significant progress has been achieved in regard to normative data for uteroplacental and fetal blood flow velocity and the factors which may affect these observations. Associations have been demonstrated between abnormal indices of maternal and fetal blood flow velocity and pregnancy-induced hypertension, fetal growth retardation, fetal blood gas measures, and intrapartum clinical fetal distress. However, in general, the predictive power is modest and no evidence has yet been provided to indicate that these measures can be used as a screening test in the general obstetric population. Continuing research is highly desirable. At the present time, the use of Doppler assessment of blood flow in pregnancy should be limited to the investigational setting.

Evaluation of blood flow velocity waveform in an animal model

Blood flow velocity waveforms in the abdominal aorta of three anesthetized pigs were recorded by a combined 3.5-MHz real-time and 2-MHz pulsed-Doppler ultrasound. The flow velocity waveforms were analyzed for pulsatility index, systolic to diastolic ratio, rising slope, descending slope, and the minimum diastolic velocity, and then were compared with volume blood flow measured by electromagnetic flowmeter (Q), mean arterial pressure (MAP), and total peripheral resistance (TPR). Total peripheral resistance was calculated according to the formula TPR = MAP/Q. A total of 111 recordings were performed over a range of heart rate: 90-250 beats/min, of Q: 65-1318 mL/min, of MAP: 72-165 mmHg and of total peripheral resistance 0.10-2.17 mmHg x min/mL. A significant positive correlation was found between pulsatility index and total peripheral resistance (correlation coefficient r ranging 0.64-0.87) and between systolic to diastolic ratio and total peripheral resistance (r: 0.59-0.83). The minimum diastolic velocity showed a negative correlation to TPR(r: -0.68 - -0.76). The pulsatility index was dependent on the heart rate, mean arterial pressure and rising slope; however, the relations were not consistent in all experiments. The results indicate that the pulsatility index is a good indicator of the flow velocity waveform changes depending on changes in the peripheral vascular resistance, and that the relationship between the total peripheral resistance and pulsatility index is linear. The systolic to diastolic ratio proved to be comparable even though it is somewhat less effective in performance than the pulsatility index.

Blood flow velocity and pulsatile diameter changes in the fetal descending aorta: a longitudinal study

Blood flow velocity and pulsatile diameter changes in the fetal descending aorta were measured subsequently with pulsed Doppler ultrasonography and phase-locked echo-tracking technique, respectively. Blood flow velocity and pulse-wave curves with equal beat-to-beat intervals were synchronized by external fetal electrocardiogram. The systolic increase in blood flow velocity and in vessel diameter started simultaneously. The velocity peak preceded the diameter peak by a significant margin (p in the range 0.0001 to 0.0014). The time interval was more pronounced in the thoracic than in the abdominal part of the aorta and was slightly smaller near term. The effective diameter, calculated from the synchronized integrals of the blood flow velocity and the diameter curves, was significantly greater (p in the range 0.0001 to 0.0016) than the mean diameter. The difference tended to decrease with advancing gestational age and was more pronounced in the thoracic than in the abdominal aorta. The maximum error incurred by the use of nonsimultaneous measurements of blood flow velocity and vessel diameter when calculating volume blood flow was found to be less than 8% and thus probably of little practical importance.

The effect of heart rate on Doppler flow velocity systolic-diastolic ratios in umbilical and uteroplacental arterial waveforms

In an analysis of the influence of heart rate on Doppler flow velocity waveform-systolic/diastolic ratios from 1555 umbilical artery waveform studies and from 1497 uteroplacental waveform studies, a negative correlation was observed between the ratio and the corresponding heart rate. This relationship was not influenced by gestational age and was similar in pregnancies with normal outcomes when compared with all pregnancies. The magnitude of this inverse relationship is such that the effect of heart rate on systolic/diastolic ratios must be considered when Doppler flow velocity waveform analyses are used as experimental tools to assess placental vascular resistance but it does not appear to be an important factor in general clinical practice when measurements are made during fetal inactivity and when heart rates are within normal ranges.

Human fetal ductal flow velocity waveforms relative to behavioral states in normal term pregnancy

In 16 normal pregnancies the relationship between the blood flow velocity waveform and fetal behavioral states at 37 to 38 weeks' gestation was studied. Whereas behavioral state independency was established for the acceleration time, peak flow velocity demonstrated a statistically significant reduction during active sleep, compared with quiet sleep. These data reflect reduced ductal flow and suggest a redistribution in the left-ventricular and right-ventricular output in favor of the left side of the heart during active sleep. Peak flow velocities in the fetal ductus arteriosus were independent of fetal heart rate.

Fetal aortic blood flow and echocardiographic findings in human pregnancy

Relationships between human fetal aortic blood flow parameters and the corresponding echocardiographic findings were investigated in 51 normal, 26 hypertensive and 18 diabetic late pregnancies. In the normal pregnancies the time-averaged mean and peak velocities and the waveform indexes of the flow in the fetal aorta were not dependent on the cardiac size nor on the fractional shortening of the myocardium. Total blood flow in the aorta correlated well with heart size and left ventricular output. Hypertensive cases had, as a group, lower aortic velocities and higher waveform indexes than normal and diabetic pregnancies, and the difference from normal was particularly great if the fetus was growth-retarded. Myocardial contractility in these fetuses remained good in spite of these peripheric hemodynamic alterations, but the relative size of the right ventricle was increased. The diabetic cases had smaller blood flow volume in fetal aorta than in the normal cases. In contrast with normal pregnancies the myocardial fractional shortening of these fetuses decreased if the pulsatility of the aortic blood flow increased or the total blood flow in the aorta was high. These findings point to a decreased functional capacity of the fetal heart in a diabetic pregnancy, in particular in the late weeks of gestation.

The blood flow velocity waveform index in the fetal thoracic aorta and its ability to detect fetal compromise in the small for gestational age fetus

In a prospective longitudinal study of 96 patients, mean values of blood velocity waveform indices of the fetal thoracic aorta are established with a combined linear array real-time and pulsed Doppler transducer. The course of the various blood velocity waveforms is elucidated. The most striking finding is the restricted variability of the pulsatility index (PI), resistance index (RI), A/B ratio, acceleration time (AcT) and acceleration time percentage (AcTP) during the last trimester of pregnancy. In 17 proven and evaluable SGA infants the various blood velocity waveform indices were compared with the established mean values. Fourteen of these 17 (82%) infants were proven to be intrauterine growth-retarded (IUGR). Only 3 of these 14 (21%) showed a significant increase in PI values.

The first derivative as a means of synchronizing pulsatile flow velocity and vessel diameter waveforms in the fetal descending aorta

In order to calculate volume flow, blood flow velocity and pulsatile vessel diameter waveforms in the lower thoracic part of the descending aorta of the fetal lamb and human fetus were matched for identical cardiac cycle length by fetal ECG and the first derivative of these waveforms. Volume flow values were not essentially different using either method. There is simultaneous onset of the blood flow velocity and pulsatile vessel diameter waveforms. The first derivative can reliably replace the fetal ECG as a means of synchronizing blood flow velocity and pulsatile vessel diameter waveforms in the fetal descending aorta.

Ultrasound measurement of fetal blood flow in predicting fetal outcome

The efficacy of fetal blood flow assessment in predicting fetal outcome was evaluated in 159 pregnancies suspected of intrauterine growth retardation (IUGR). Blood flow in the fetal aorta and umbilical vein was measured with imaging and pulsed Doppler ultrasound. Volume blood flow values and variables describing the waveform of the maximum aortic blood velocity were checked for relations to subsequent fetal outcome. A new semi-quantitative velocity waveform variable, blood flow class (BFC), was designed and tested. The occurrence of IUGR, imminent fetal distress, a low Apgar score at 1 and 5 min, and a low pH in the umbilical artery and vein were adopted to characterize fetal outcome. Receiver operating characteristic curves were used to demonstrate the sensitivity and false positive rate, and the Cohen's Kappa index was used to compare the predictive capacity of the various blood flow variables. BFC, describing the blood velocity waveform with emphasis on its end-diastolic part, was found to be the most powerful marker of imminent fetal asphyxia (Kappa = 0.66) and of intrauterine growth retardation (Kappa = 0.48).

Fetal and uteroplacental haemodynamics during short-term atenolol treatment of hypertension in pregnancy

Fetal circulation was studied by means of combined real-time and pulsed Doppler ultrasound in 14 women with pregnancy-associated hypertension before and during the first and third days of treatment with the beta 1-selective blocker, atenolol; in seven of the women the maternal uterine arcuate blood velocity waveform was also studied. Blood flow characteristics were normal both in the fetus and in the maternal arcuate artery, compared with those in uncomplicated pregnancies of corresponding gestational ages. Volume blood flow remained unchanged in the fetal descending aorta, and in the umbilical vein during atenolol treatment, whereas the pulsatility index increased in the fetal descending aorta and in the arcuate artery. This suggests that the peripheral vascular resistance, both on the maternal and fetal side of the placenta, increased during short-term antihypertensive treatment with atenolol.

Circulatory changes in the fetal aorta after maternal smoking

The acute cardiovascular responses of the human fetus to maternal smoking of one cigarette were studied in 10 healthy pregnant women. Following maternal smoking, a significant increase was found in the nicotine concentration in maternal plasma accompanied by a significant increase in the fetal heart rate. The flow velocity was recorded in the fetal descending aorta by combining real-time ultrasonography and the 2 MHz pulsed Doppler technique and the waveform of the maximum blood velocity was analysed. The duration of the acceleration part of the pulse cycle (start-to-peak time) remained unchanged during the study period. The least diastolic blood velocity increased significantly after smoking. The pulsatility index fell significantly during the first 5 min after smoking, probably as the consequence of fetal tachycardia, but was normal again at 10 min. The rising slope rose significantly within the first 10 to 20 min after the onset of smoking. The results indicate, that, following maternal smoking of one cigarette, fetal central circulation increases but peripheral resistance is unchanged.

Fetal blood flow in diabetic pregnancy

Forty pregnant diabetic women were examined with combined Doppler and real-time ultrasound. The volume blood flow in the fetal aorta and umbilical vein was higher and the pulsatility index (PI) in the aorta lower in the early third trimester, as compared with a reference group. Near term, the umbilical artery PI was higher in diabetic than in non-diabetic pregnancies, indicating a higher placental vascular resistance in the former group. The high umbilical artery PI occurred in fetuses who later developed distress in labor. Therefore, a high umbilical artery PI cannot be considered characteristic of diabetic pregnancy, although fetal distress might be more common in diabetic pregnancy. In addition, a high aortic volume flow was found in those fetuses who later develop distress in labor. This might be an expression of an early compensatory mechanism for increased placental vascular resistance. No specific flow variation was observed for any White class, or in association with hypertension or non-optimally regulated diabetes. The blood flow variables in growth-accelerated fetuses were comparable to those found in fetuses with normal weight. Since fetal distress might be more common in diabetic pregnancy, ultrasonic fetal blood flow measurements are recommended for antenatal fetal surveillance.

Clinical outcome and circulatory effects of fetal cardiac arrhythmia

By means of abdominal fetal ECG and non-invasive ultrasound blood flow studies 113 cases of fetal cardiac arrhythmia were classified according to the origin of arrhythmia. Pregnancy outcome was characterized by an increased frequency of fetal distress and heart malformation, and increased fetal and neonatal mortality. The following types of arrhythmia were identified: supraventricular extrasystoles (n = 84), paroxysmal tachycardia (n = 6), sinus bradycardia (n = 3), atrial flutter (n = 1), ventricular extrasystoles (n = 14), and atrioventricular block (n = 5). In 37 cases the combined Doppler and real-time ultrasound technique was used to measure fetal aortic blood flow as a means of studying the circulatory effects of the arrhythmia. Increased peak velocity, rising slope and acceleration were found in the first post-pausal beat after a supraventricular extrasystole or a missed beat; this supports the validity of Frank-Starling law for the fetal heart and suggests that a strong relationship exists between these variables and myocardial contractility. In two cases of intra-uterine heart failure, the effect of digoxin treatment in utero on the fetal aortic flow variables was studied, results indicating a positive inotropic effect of the drug on the fetal myocardium. The estimation of fetal aortic volume blood flow in cases of fetal cardiac arrhythmia is useful for early detection of fetal cardiac failure, and for monitoring the effects of intra-uterine treatment.

Circulatory effects of fetal cardiac arrhythmias

The circulatory consequences of cardiac arrhythmia and its compensatory mechanisms were examined in utero in 37 fetuses. A combined real-time and 2-MHz pulsed Doppler technique was used to measure blood velocity for waveform analysis and flow estimation in the descending thoracic aorta of the fetuses. The pattern of blood velocity in the inferior vena cava was studied to classify the arrhythmia. Despite severe cardiac arrhythmias the aortic blood flow was within normal limits in all but one fetus which had associated cardiac malformation and congestive failure. The rising slope and the peak value of the maximum aortic velocity were significantly increased in the postpremature beats and in fetuses with atrioventricular block. The results support the validity of Frank-Starling's law for the fetal myocardium.