Tjeerd W.A. Huisman

DUCTUS VENOSUS BLOOD FLOW VELOCITY WAVEFORMS IN THE HUMAN FETUS--A DOPPLER STUDY

Successful human fetal ductus venosus flow velocity waveform recording was achieved cross sectionally in 48 out of 60 women at 19-22, 27-30 and 36-39 weeks of gestation. The ductus venosus shows a pulsatile flow pattern consisting of a systolic and diastolic forward component without a late diastolic reverse component as demonstrated in the inferior vena cava. Peak systolic velocities as high as 40-80 cm/s were observed. A statistically significant increase in time-averaged velocity, peak systolic and peak diastolic velocity with advancing gestational age was established.

Flow velocity waveforms in the fetal inferior vena cava during the second half of normal pregnancy

Fetal inferior vena cava (IVC) flow velocity waveform recording was attempted at the entrance into the right atrium in 60 women at 19-22 weeks, 27-30 weeks and 36-39 weeks of gestation. Technically acceptable waveforms were collected in 48 women. A significant increase in time-averaged velocity and a significant decrease in percent reverse flow with advancing gestational age was established. A large standard deviation was observed for various IVC waveform parameters. From preliminary postmortem data it appeared that the inferior venous entrance into the right atrium represents a funnel-like structure composed of the inlet of the IVC, hepatic veins and ductus venosus. It is suggested that waveform recording at the scanning level employed in the present study provides information on gestational age-related changes in venous return to the right atrium rather than changes in the IVC itself. It is proposed that information on IVC flow velocity waveforms should be obtained more distal to the venous entrance into the right atrium.

Fetal Venous and Arterial Flow Velocity Wave Forms between Eight and Twenty Weeks of Gestation

Our purpose was to study the nature and gestational age dependency of fetal venous Doppler flow velocity wave forms and their relationship with fetal arterial wave forms in early pregnancy. Venous and arterial Doppler recordings were performed in 262 normal singleton pregnancies according to a cross-sectional study design at 8-20 wk of gestation. A statistically significant age-dependent increase is established for the umbilical vein, ductus venosus, and inferior vena cava time-averaged velocity. Umbilical venous pulsatile flow patterns are observed up to 15 wk of gestation. The pulsatility index for veins in all three venous vessels displays a gestational age-dependent reduction. No relation can be established between the pulsatility index for veins and the pulsatility index in the descending aorta and umbilical artery. This may be explained by the fact that the pulsatility index for veins reflects cardiac ventricular preload, whereas the pulsatility index in the arterial vessels reflects down-stream impedance at fetal placental level.Our purpose was to study the nature and gestational age dependency of fetal venous Doppler flow velocity wave forms and their relationship with fetal arterial wave forms in early pregnancy. Venous and arterial Doppler recordings were performed in 262 normal singleton pregnancies according to a cross-sectional study design at 8-20 wk of gestation. A statistically significant age-dependent increase is established for the umbilical vein, ductus venosus, and inferior vena cava time-averaged velocity. Umbilical venous pulsatile flow patterns are observed up to 15 wk of gestation. The pulsatility index for veins in all three venous vessels displays a gestational age-dependent reduction. No relation can be established between the pulsatility index for veins and the pulsatility index in the descending aorta and umbilical artery. This may be explained by the fact that the pulsatility index for veins reflects cardiac ventricular preload, whereas the pulsatility index in the arterial vessels reflects downstream impedance at fetal placental level.

FLOW VELOCITY WAVEFORMS IN THE DUCTUS VENOSUS, UMBILICAL VEIN AND INFERIOR VENA CAVA IN NORMAL HUMAN FETUSES AT 12-15 WEEKS OF GESTATION

The objective was to determine the normal Doppler flow velocity waveform patterns in the human fetal ductus venosus, inferior vena cava and umbilical vein correlated with fetal heart rate, and to examine their reproducibility and their inter-relationship at 12 to 15 weeks of gestation. Cross-sectional recordings of 45 normal pregnant women were collected for a data reference range transvaginally and transabdominally depending on fetal size and position. Maximum flow velocity waveforms were obtained from the ductus venosus, the intra-abdominal part of the umbilical vein and inferior vena cava. Time-averaged velocities were calculated in all three vessels together with peak systolic, peak diastolic and time-averaged velocities in the ductus venosus and inferior vena cava. Doppler recordings in 21 other patients displayed good reproducibility. Continuous forward flow in the umbilical vein was associated with pulsatile systolic and diastolic forward flow in the ductus venosus. Retrograde flow was present only in the inferior vena cava. Mean time-averaged velocity (SD) in the ductus venosus was 28.8 (6.1) cm/s, in the umbilical vein 9.7 (2.9) cm/s and in the inferior vena cava 10.9 (2.5) cm/s. No correlation could be established between waveform parameters and fetal heart rate. Combined transvaginal and transabdominal Doppler ultrasound allows reproducible blood flow velocity recordings at venous level in early pregnancy. Relatively high velocities were observed in the ductus venosus compared with the umbilical vein and inferior vena cava. Differences in flow velocities in the ductus venosus and inferior vena cava suggest that little or no mixing of blood occurs, a situation well described in sheep.

RECOGNITION OF A FETAL SUBDIAPHRAGMATIC VENOUS VESTIBULUM ESSENTIAL FOR FETAL VENOUS DOPPLER ASSESSMENT

ABSTRACT: Ultrasonic visualization of the human fetal subdiaphragmatic area demonstrated anatomical relationships, different from descriptions in the literature. Four human fetal postmortem specimens at 18, 26, 28, and 34 wk of gestation were examined to ascertain morphologic details of intra- and perihepatic vasculature. Drawings of these dissected preparations were compared with ultrasonic images from the same region. With both methods the presence of a venous vestibulum immediately proximate to the diaphragm could be demonstrated. The abdominal inferior vena cava ends in a funnel-like structure, which also contains the orifices of the hepatic veins, the ductus venosus, and a phrenic vein. A considerable variability in Doppler flow recordings could result from blood propelling out of these various vessels into the vestibulum. It is, therefore, suggested that information on blood-flow velocities in venous hepatic vessels should be obtained more distally in the separate vessels and not at the entrance into the right atrium.

Intracerebral, aortic, and umbilical artery flow velocity waveforms in the late-first-trimester fetus

OBJECTIVES Our objectives were to determine the success rate in obtaining flow velocity waveforms in the first-trimester fetal circulation and to establish possible preferential flow to the fetal cerebrum at this early stage of gestation. STUDY DESIGN Flow velocity waveform recordings were made in the umbilical artery, fetal descending aorta, and fetal intracerebral arteries in 30 normal pregnancies between 11 and 13 weeks of gestation. RESULTS Technically acceptable waveforms were obtained from the descending aorta in 15 fetuses, from the intracerebral circulation in 17 fetuses, and from the umbilical artery in all 30 fetuses. Absent end-diastolic velocities in the descending aorta and umbilical artery were associated with forward flow throughout the cardia cycle in intracerebral arteries. CONCLUSION A relatively low cerebral vascular resistance in the late-first-trimester normal fetus is suggested.

Ductus venosus flow velocity waveforms in relation to fetal behavioural states

Objectives To establish the reproducibility of flow velocity waveforms in the human ductus venosus and to assess the influence of fetal behavioural states on these waveforms in normal term fetuses.

Fetal cardiac flow velocities in the late 1st trimester of pregnancy: a transvaginal Doppler study.

In 30 normal women with a singleton pregnancy, transvaginal Doppler ultrasound was used to record flow velocity at the fetal atrioventricular (AV) valve and outflow tract levels (ascending aorta and pulmonary artery) at 11 to 13 weeks of gestation. Technically acceptable flow velocity waveforms were recorded at the AV valve level in 19 fetuses and in the ascending aorta and pulmonary artery in 15 and 17 fetuses, respectively. Successful documentation of both transmitral and transtricuspid flow velocity waveforms was achieved in six fetuses only. Peak velocities during atrial contraction (A wave) were nearly twice as high as those during early diastolic filling (E wave), reflecting low ventricular compliance. Peak and time-averaged flow velocities in the outflow tract were lower than those observed in 2nd and 3rd trimester pregnancies with mean values of 32.1 +/- 5.4 (+/- SD) and 11.2 +/- 2.2 cm/s, respectively, in the ascending aorta and 29.6 +/- 5.1 and 10.8 +/- 2.1 cm/s in the pulmonary artery.

Normal fetal Doppler inferior vena cava, transtricuspid, and umbilical artery flow velocity waveforms between 11 and 16 weeks' gestation.

OBJECTIVES Our objectives were to determine flow velocity waveform patterns in the fetal inferior vena cava and to relate these waveforms to transtricuspid and umbilical artery waveforms and fetal heart rate in early gestation. STUDY DESIGN Doppler waveforms were recorded in 40 normal fetuses at 11 to 16 weeks of gestation. Only transvaginal scanning was carried out at 11 to 12 weeks and only transabdominal scanning was used at 15 to 16 weeks. RESULTS The ratio of time velocity integrals of flow from the inferior vena cava during systole and early diastole, the percentage of reverse flow in this vessel, the pulsatility index from the umbilical artery, and the fetal heart rate were negatively correlated with gestational age. Peak E-wave and A-wave velocities and E/A ratios from the transtricuspid waveforms were positively correlated with gestational age. CONCLUSION Early normal pregnancies are associated with remarkable changes in fetal flow velocity waveforms at both the cardiac and the extracardiac level.

There are no rest-activity dependent changes in fetal ductus arteriosus flow velocity patterns at 27–29 weeks of gestation

Blood flow velocity waveforms recorded in the fetal ductus arteriosus were related to fetal heart rate pattern (FHRP) in 13 normal pregnancies at 27-29 weeks of gestation. Recording time was always 65 min or more. In three women no low fetal heart rate (FHRP-A) variability was present, in the remaining 10 women high fetal heart rate (FHRP-B) variability was established in 80% of the recording time. There was no statistically significant difference between FHRP-A and FHRP-B pattern for all ductal flow velocity parameters, indicating rest-activity state independency in late second and early third trimester pregnancy.