Blood flow velocities in human intraplacental arteries.

OBJECTIVE: To characterise the physiological findings of blood circulation in intraplacental arteries in normal and complicated pregnancies. DESIGN: A descriptive cross-sectional study. Umbilical and intraplacental artery resistance index (RI) Doppler recordings during the last trimester of pregnancy. SUBJECTS: Forty-nine normal pregnancies and ten pregnancies complicated by fetal growth retardation. RESULTS: RI values decreased from the proximal umbilical artery to the distal umbilical artery and to intraplacental arteries. All of these vessels had decreasing RI values towards the end of pregnancy. In pathological pregnancies an abnormal flow pattern in umbilical arteries could be associated with either an abnormal or normal flow pattern in the intraplacental arteries. CONCLUSIONS: Blood flow in intraplacental arteries can be recorded by sensitive color Doppler in normal pregnancies, but in complicated pregnancies variation of the Doppler findings, together with imaging difficulties of intraplacental arteries, seem to impair the applicability of this examination as a diagnostic tool.

Fetal and preterm newborn cerebral blood flow velocity.

Using Doppler ultrasound, cerebral blood flow velocities (CBFV) in the first month of life of normoxemic preterm infants born in the 28th gestational week with stable circulatory conditions were examined. The results were compared with fetal CBFV in the 28th to 32nd weeks of pregnancy. Peak systolic (PSV), end-diastolic (EDV) and time averaged maximum velocities (TAMV) were evaluated from the Doppler shifts recorded from the middle cerebral artery (MCA). Cerebral circulatory changes in neonates in the first 4 weeks of life were much more pronounced than in fetuses at the corresponding gestational age (28-32 weeks). After the rapid increase in neonatal CBFV in the first 3 weeks of life, our results appear to indicate a stabilisation between the 3rd and 4th week (corresponding to the 32 gestational weeks). The significance of, and possible mechanisms for, these changes are discussed.

[Are Doppler methods suitable for the study of adaptive maternal central circulatory regulation in pregnancy? II. Assessment of time parameters and determination of minute distance, conclusions]. / Sind Dopplermethoden geeignet zur Untersuchung adaptiver mütterlicher zentraler Kreislaufregulation in der Schwangerschaft?Teil II. Erfassung von Zeitparametern und Bestimmung der Minute Distance, Schlussfolgerungen.

Echocardiographic Doppler measurements of blood flow velocity are a noninvasive way of studying maternal central haemodynamics. Part 2 reports on additive and derived physiological parameters using different Doppler ultrasound techniques. This paper shows that quantitative assessment of adaptive maternal central circulatory regulation must be interpreted in respect of methods and machines. Technical requirements to be met by the Doppler equipment to avoid present limitations are discussed as are various aspects involved in such studies.

[Are Doppler methods appropriate for the study of adaptive maternal central circulation regulation in pregnancy?]. / Sind Dopplermethoden geeignet zur Untersuchung adaptiver mütterlicher zentraler Kreislaufregulation in der Schwangerschaft?

Echocardiographic Doppler measurements of blood flow velocity are a noninvasive way of studying maternal central haemodynamics. Part 1 reports on conditions as well as on practical and theoretical problems recognized as contributing significantly to the use and interpretation of Doppler ultrasound techniques in the assessment of adaptive central circulatory regulation in pregnancy. The significance of different techniques is shown by assessments of the peak velocity and the velocity time integral.

Uteroplacental blood flow velocity waveforms in the second and third trimesters of normal pregnancy as related to the placenta location.

The systolic/diastolic ratios (A/B) of uteroplacental blood flow velocity waveforms as related to the placenta location were investigated by continuous-wave Doppler ultrasound in 67 normal pregnancies at 18-21 weeks, in 111 at 31-33 weeks, and in 34 at 40-41 weeks of gestation. Using real-time ultrasound, the placenta was located laterally in 48%, posteriorly in 30% and anteriorly in 22% of the pregnancies. A/B values decreased slightly with advancing gestational age. With lateral placenta location, statistically significant higher A/B values were found in vessels on the nonplacental side at 31-33 weeks of gestation (2.07 +/- 0.43 versus 1.74 +/- 0.27; p less than 0.05). In the other gestational age groups there were no statistically significant differences between A/B values in the vessels on the placental and nonplacental sides. There were also no differences in A/B values between left and right uteroplacental vessels with anterior or posterior placenta locations in any of the gestational age groups.

Uteroplacental blood flow velocity waveforms as a predictor of adverse fetal outcome and pregnancy-induced hypertension.

The resistance index (RI) of uteroplacental blood flow velocity waveforms (VWF) was investigated by continuous Doppler ultrasound in 286 nonselected pregnant women with singleton pregnancies at 18-21 weeks (n = 129) and at 31-33 weeks (n = 157) of gestation to evaluate the validity of this method as a screening procedure for abnormal pregnancy outcome (intrauterine growth retardation, pregnancy-induced hypertension and fetal asphyxia). The sensitivity of predicting pregnancy outcome was 26.6% at 18-21 weeks and 17.6% at 31-33 weeks of gestation. It was concluded that this method is too insensitive as a screening tool for the prediction of intrauterine growth retardation and pregnancy-induced hypertension in a low-risk nonselected pregnant population.

Determination of the minimum number of cardiac cycles necessary to ensure representative blood flow velocity measurements.

The aim of this study was to determine the minimum number of cardiac cycles necessary over which blood flow velocity representative of the situation (and not unduly influenced by sporadic irregularities). Blood flow was measured by Doppler ultrasound in the adult a. carotis communis, a. femoralis and fetal a. umbilicalis. The coefficients of variation (CV) for the Pulsatility Index (PI), Resistance Index (RI) and Time Average of Space Average Velocities (TASAV) from 10 averaged cycles were compared with the CVs of the respective indices from 2, 3, 4 up to 9 averaged cycles. The number of averaged cycles where the difference between the coefficients of variability became insignificant (Wilcoxon signed rank test) was taken to be the point at which representative values of PI, RI or, respectively, TASAV are assured. For PI evaluation for the a. carotis communis with either the 7 mx or 15 mx calculation program one needs to average over 7 cardiac cycles. Manually determining the maximum frequency curve envelope, 5 cycles are sufficient. Using these same calculation programs for the a. femoralis, 5, 6 and, respectively, 6, cycles are sufficient for representative PI indices; for the umbilical artery, 6, 8 and, respectively, 7 cycles are necessary. For RI, 5 cycles are sufficient in both the a. carotis communis and a. umbilicalis by manual evaluation. For TASAV, a minimum of 3 cycles for the a. carotis communis and of 7 for the a. femoralis are necessary. Thus the number of cardiac cycles which should be averaged is dependent on the vessel being examined, the index being calculated, and the program being used.