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.

Fetal bradyarrhythmia: diagnosis and outcome.

Seventeen patients were referred to out ultrasound unit because of fetal bradyarrhythmia (less than 100 bpm). Duration of pregnancy varied between 21 and 40 weeks. Bradyarrhythmia was diagnosed as atrioventricular block (n = 12), mild sinus bradycardia (n = 3), and irregular bradycardia (n = 2). The association with maternal collagen disease was 29 per cent and with cardiac structural defects 59 per cent. The overall mortality was 41 per cent. There were three abnormal karyotypes (17 per cent) and four cases of cardiac compromise (23 per cent). Prognosis depends on the nature of the bradyarrhythmia and recognition of associated pathology such as cardiac structural defects, abnormal karyotype and degree of cardiac compromise.

Cerebral and umbilical arterial blood flow velocity waveforms in normal and growth-retarded pregnancies.

A combined sector and pulsed Doppler system was used to study the pulsatility index in the fetal internal carotid artery and umbilical artery in 156 normal pregnancies and 42 cases of intrauterine growth retardation (birth weight below the tenth percentile). All pregnancies were in the third trimester. In normal pregnancies, there was a gestational age-related fall in pulsatility index for both the umbilical artery and the umbilical artery/internal carotid artery ratio. No such fall was established for the pulsatility index in the internal carotid artery. In growth-retarded pregnancies, raised pulsatility index values in the umbilical artery were associated with reduced pulsatility index values in the internal carotid artery, suggesting the presence of a "brain-sparing" effect. When fetal causes of growth retardation were excluded, the sensitivities of the pulsatility index in the internal carotid artery, the umbilical artery, and for the umbilical artery/internal carotid artery ratio were 65, 83, and 88% at the 1 standard deviation (SD) cutoff level; and 48, 60, and 70% at the 2 SD cutoff level. Growth-retarded fetuses with structural or chromosomal defects had normal pulsatility index values in the internal carotid artery.

Fetal blood flow velocity waveforms in relation to changing peripheral vascular resistance.

In an acute experiment in Texel ewes, Doppler flow velocity waveforms from the fetal descending aorta were related to peripheral vascular resistance as calculated from perfusion pressure divided by electromagnetically measured volume flow in the descending aorta. Vascular resistance was increased by stepwise embolization of the peripheral circulation via repeated bolus administration of Sephadex G-25 microspheres. A rise in peripheral vascular resistance was associated with a reduction in peak and end-diastolic flow velocity and an increase in Pulsatility Index. Clinically, if similar changes are observed in growth retarded fetuses, the findings are usually interpreted to represent 'uteroplacental insufficiency'. Present data provide direct evidence that raised peripheral vascular resistance does indeed produce such waveform changes.

Fetal cardiac arrhythmias and their effect on volume blood flow in descending aorta of human fetus.

Using a two-dimensional linear array real-time and pulsed Doppler ultrasound system, volume blood flow measurements were made in 86 normal pregnancies, seven cases of fetal bradycardia, and seven cases of fetal tachycardia at the lower thoracic level of the fetal descending aorta. During fetal cardiac arrhythmias, volume blood flow was maintained within the normal range until the heart rates reached around 50 bpm and 230 bpm, after which the volume blood flow diminished. The changes observed suggest that the Frank-Starling mechanism is functional in the fetal myocardium and demonstrate the stability of the fetal circulation.

The blood flow velocity waveform in the fetal descending aorta; its relationship to behavioural states in the growth-retarded fetus at 37-38 weeks of gestation.

In 12 patients with intrauterine growth retardation (IUGR), the relationship between the blood flow velocity waveform at the lower thoracic level of the fetal descending aorta and fetal behavioural states at 37-38 wk of gestation was studied. A significant inverse relationship (P less than 0.001) was established between pulsatility index (PI) and fetal heart rate (FHR) in state 1F and 2F. The PI as a measure of peripheral vascular resistance, demonstrated a marked increase compared to normal pregnancy. There is a virtual overlap of PI values originating from state 1F and 2F according to the classification by Nijhuis et al. (J.G. Nijhuis, H.F.R. Prechtl, C.B. Martin, Jr. and R.S.G.M. Bots (1982) Early Hum. Dev. 6, 177-195). The peripheral vasoconstriction present in IUGR seems to overrule state dependent PI fluctuations. The marked rise in PI, particularly at lower FHR and the constancy of PI in relation to fetal behavioural states can be considered vascular adaptations, which are instrumental in the centralization of the fetal circulation, with the aim of favouring blood supply to the brain, heart and adrenals during IUGR.

Severe intrauterine growth retardation; assessment of its origin from fetal arterial flow velocity waveforms.

Doppler blood flow velocity waveforms in the umbilical artery and fetal internal carotid artery were recorded in a total of 10 patients with severe intrauterine growth retardation (IUGR) and marked oligohydramnios to establish a fetal or utero-placental origin of IUGR. Gestational age varied between 28 and 37 wk. Negative maternal serology ruled out fetal infections. In six patients, IUGR was associated with abnormal flow velocity waveforms, indicating utero-placental insufficiency. Following delivery, these infants showed no structural defects; moderate to marked placental infarction was documented in 4 out of 6 cases. In the remaining four patients, IUGR was associated with normal flow velocity waveforms, suggesting a fetal origin of the IUGR. Following delivery, all four infants revealed structural defects, only one of which was diagnosed prenatally. Twice an abnormal karyotype was the underlying cause. There was no placental infarction. These preliminary data suggest that combined recording of the flow velocity waveform in the above-mentioned vessels may provide valuable additional information as to the cause of IUGR and as such be helpful in determining obstetric management.

Blood flow velocity waveforms in the descending fetal aorta: comparison between normal and growth-retarded pregnancies.

A linear array real-time transducer was combined with a pulsed Doppler transducer to study and compare the mean blood flow velocity waveform in 77 normal pregnancies and 12 cases of intrauterine growth retardation. All pregnancies were in the third trimester. In normal pregnancies the peak velocity, end diastolic velocity, and pulsatile index remained unchanged with increasing gestational age. End diastolic velocity was lowered or at zero level (high pass filter level), and the pulsatile index was elevated in most cases of severe intrauterine growth retardation. Peak velocity related closely with the quality of the heart rate patterns and the condition of the infant at birth.

Doppler ultrasound assessment of cerebral blood flow in the human fetus.

A mechanical sector and linear array real-time scanner combined with a pulsed Doppler system was used for recording the flow velocity waveform in the internal carotid artery, the lower thoracic part of the descending aorta and umbilical artery in the human fetus. A total of 42 fetuses in normal pregnancy and nine growth-retarded fetuses between 26 and 41 weeks gestation was studied. In normal pregnancy the mean pulsatility index (PI) in the internal carotid artery varied between 1.5 and 1.6, in the descending aorta between 1.7 and 1.8 and in the umbilical artery between 0.7 and 1.3. In the growth-retarded fetuses the PI was reduced in the internal carotid artery and raised in the descending aorta and umbilical artery, suggesting an increased peripheral vascular resistance in the fetal body and placenta and a compensatory reduction in peripheral vascular resistance in the fetal cerebrum, i.e. a brain-sparing effect in the presence of fetal hypoxia.

The blood flow velocity waveform in the fetal descending aorta: its relationship to fetal behavioural states in normal pregnancy at 37-38 weeks.

In 13 normal pregnancies, the relationship between the blood flow velocity waveform at the lower thoracic level of the fetal descending aorta and fetal behavioural states at 37-38 weeks of gestation was studied. The pulsatility index (PI), as a measure of peripheral vascular resistance, was significantly lower during state 2F compared to state 1F according to the classification by Nijhuis et al. (Nijhuis, J.G. et al. (1982) Early Hum. Dev., 6, 177-195), suggesting an increased perfusion of the fetal skeletal musculature to meet the energy demand needed for the raised muscular activity during state 2F; A significant inverse relationship (P less than 0.001) was established between PI and FHR in state 2F; this was mainly determined by a significant rise in end-diastolic flow velocity (P less than 0.02). Both the behavioural state and FHR should be taken into account when evaluating flow velocity waveforms in the fetal descending aorta during the latter weeks of pregnancy.

Fetal blood flow measurements during fetal cardiac arrhythmia.

3 cases of fetal complete heart block, 1 case of fetal bradycardia and 2 cases of fetal supraventricular tachycardia were studied. Using an ultrasonic technique combining real-time ultrasound with a pulsed Doppler system, blood flow measurements at the lower thoracic level of the fetal descending aorta were taken. Despite alterations in rhythm, the blood flow in the aorta descendens was maintained within normal range. With a reduced heart rate, there was an increase in stroke volume, blood flow velocity, acceleration of blood flow velocity and maximum diameter change; conversely, with an increased heart rate the same four parameters were lowered. These alterations reflect changes in cardiac contraction force, and illustrate the ability of the fetal myocardium in maintaining blood flow in the growing fetus.

The role of diagnostic ultrasound in the study of fetal cardiac abnormalities.

Between January 1982 and April 1983, a total of 315 patients was scanned for fetal Congenital Heart Disease (CHD). In 70% of these patients, there was an increased risk for CHD in their offspring, in the remaining 30% abnormal findings were made by ultrasound in the present pregnancy. Nine cardiac defects were correctly diagnosed. There were three false positive and three false negative findings. The presence of fetal dysrhythmia, Intra-Uterine Growth Retardation (IUGR), ascites or polyhydramnios warrants a structural analysis of the fetal heart. Prenatal scanning for CHD should preferably be carried out in centres which can guarantee a high degree of scanning experience, up-to-date scanning equipment and close cooperation with a well-established neonatal and pediatric cardiology unit.

Blood flow measurements in the fetal descending aorta: technique and clinics.

A combination of two-dimensional and realtime pulsed-Doppler ultrasound provides a noninvasive method of measuring human fetal blood flow without side effects. By not altering the physiological conditions of the fetus, it minimizes external stimuli that might affect blood flow. However, due to the inaccessibility of the vessels under investigation, errors from the ultrasound technique arise and these are still being assessed. Studies of fetal blood flow suggest that the fetal circulation has a low peripheral resistance and that the increase in blood flow found with increasing gestational age is due predominantly to the increase in the actual dimensions of the fetal vasculature. Investigations in abnormal pregnancies, such as small-for-dates and those with cardiac arrhythmias have shown that the fetal cardiovascular system is capable of compensating efficiently to maintain normal physiological conditions, but only within the limits defined by the Frank Starling mechanism.

Arrhythmia and structural abnormalities of the fetal heart.

Thirty fetuses with cardiac arrhythmias were referred for ultrasonography. This included cross sectional and M mode echocardiography and pulsed Doppler analysis of the fetal heart. Three types of arrhythmias were observed: ectopic beats, tachyarrhythmias, and bradycardia. Ectopic beats were associated with cardiac structural abnormalities in two cases, resulting in fetal death in one. Tachycardia was not associated with structural defect, but death from cardiac failure occurred in one patient. Transplacental treatment for tachyarrhythmia was not successful in our experience. In the group with bradycardia four cases had congenital cardiac abnormalities and the mortality rate was 50%. When a fetal cardiac arrhythmia has been established careful structural and rhythm analysis is of vital importance in facilitating prognosis, planning of time and mode of delivery, and monitoring of transplacental treatment where indicated.

Vascular dynamics in the descending aorta of the human fetus in normal late pregnancy.

Fetal blood flow velocity and diameter changes in the lower thoracic part of the descending aorta were compared in twenty normal pregnancies between the gestational age of 30 and 41 weeks. The mean blood flow velocity remained constant throughout the study period whereas a significant increase in vessel diameter was observed. The significant increase in aortic stroke volume and blood flow was in correlation with this diameter change.

Cardiac ventricular geometry and function in the growth-retarded fetus.

M-mode recordings of the fetal cardiac ventricles were studied in 15 pregnant women with fetal growth retardation. Pregnancy duration varied between 28 and 40 weeks of gestation. In the presence of normal fetal heart rate patterns, M-mode assessment of ventricular geometry and function did not provide additional information on fetal condition. A close relationship between left ventricular output and fetal weight could be demonstrated.