The use of an indwelling Doppler probe to study acute changes in umbilical artery waveforms in the fetal sheep

Doppler blood flow velocity waveforms of the umbilical artery during variable decelerations in labor

OBJECTIVE

To investigate the changes in resistance indices of blood flow velocity waveforms of the umbilical artery (UmA-RIs) during variable decelerations (VDs) vs. early decelerations (EDs).

METHODS

UmA-RIs were measured before and during uterine contractions in 30 cases with VDs, nine cases with EDs and 20 cases without decelerations. In 12 out of 30 cases with VDs, UmA-RI was determined at the following five stages of a VD; before the deceleration, downward, bottom, upward and resumption stages.

RESULTS

UmA-RIs during VDs were significantly higher compared with those at preceding periods. UmA-RIs at downward and bottom stages of VDs were significantly higher than those at the upward stage, although no differences in heart rate were found between downward and upward stages. UmA-RIs during EDs or uterine contractions without decelerations did not differ from those preceding them.

CONCLUSION

UmA-RIs increased during VDs, particularly at downward and bottom stages during which the cord seemed to be actually compressed.

CK-BB as indicator of prenatal brain-cell injury in fetuses with absent or reverse end-diastolic flow velocities of the umbilical arteries

The purpose of this study is to determine the levels of brain type isoenzyme of creatine kinase (CK-BB) as a possible indicator of a pre-existing intrauterine brain-cell damage in cord blood sera of fetuses with preceding absent or reverse end-diastolic flow velocities of the umbilical arteries (AREDFV). CK-BB isoenzyme activities were determined in umbilical cord sera of 13 newborn infants with preceding AREDFV and in 14 fetuses with low end-diastolic flow velocities (LEDFV) of the umbilical arteries. 50 newborn infants with elective cesarean section and normal umbilical artery blood flow velocity waveforms were used as controls. Two-tailed Student's t-test and Fischer's exact test were used for statistical evaluation of the results. CK-BB isoenzyme activity did not depend on gestational age. Fetuses with AREDFV showed a significant increase in CK-BB values, whereas fetuses with LEDFV had CK-BB activities within the normal range of the controls. The elevated CK-BB values of the AREDFV group were not correlated with fetal acidosis at birth. Brain-cell injury with leakage of CK-BB isoenzyme might be present in fetuses with AREDFV even before (preterm) delivery.

Blood flow velocity waveforms of the middle cerebral artery and abnormal neurological evaluations in live-born fetuses with absent or reverse end-diastolic flow velocities of the umbilical arteries

We studied 37 fetuses with absent or reverse end-diastolic flow velocities (AREDFV) of the umbilical arteries with respect to the mode of delivery, fetal acidosis, resistance index of the middle cerebral arteries, and abnormal neurological evaluation at the time of discharge from the department of pediatrics. A control group with normal umbilical artery flow velocity waveforms was matched for gestational age. Fetuses with AREDFV were delivered almost exclusively by cesarean section, in most cases due to fetal distress. Metabolic changes with decreased base excess values were found more often in fetuses with AREDFV, but no difference could be detected with respect to severe fetal acidosis. The number of fetuses with abnormal neurological evaluations during the first 6 months of life was significantly higher in cases with AREDFV than in the control group. More than two thirds of the fetuses with AREDFV showed an abnormal blood flow velocity waveform of the middle cerebral arteries with elevated end-diastolic flow velocities. The combination of extreme premature delivery before 28 weeks of gestation, severe idiopathic respiratory distress syndrome, and a resistance index of the middle cerebral arteries under the 5th percentile seems to be a risk factor for early neurological morbidity in fetuses with AREDFV. Premature delivery of fetuses with AREDFV--as we did during our study in order to prevent intra-uterine death or fetal asphyxia--should therefore be critically regarded in cases under 28 weeks of gestational age and abnormal flow velocity waveforms of the middle cerebral arteries.

The physiologic mechanisms of variable decelerations

OBJECTIVES

The purpose of this study was to determine the cause and physiologic consequences of variable decelerations.

STUDY DESIGN

Previous studies of heart rate changes in human and experimental animals were critically reviewed with respect to the autonomic nervous system component, the cause of the increased vagal activity, and the role of cord compression or other stimuli in these heart rate changes.

RESULTS

There is abundant evidence from experimental and human studies that variable decelerations can be reproduced by either cord compression or head compression. The vagal reflex produced is probably caused by a combination of chemoreflex (earlier in the deceleration) and baroreflex (later). The variable deceleration is accompanied by an acidosis, primarily respiratory, and probably hypoxemia. Cord compression results in decreased umbilical blood flow.

CONCLUSIONS

Recent Doppler velocimetry studies suggest that even though the variable decelerations may be similar in duration and depth, the reduction of umbilical blood flow may be greater when the prime cause is cord compression than when the prime cause is vagal reflex from another source.

Fetal middle cerebral artery blood flow during normal active labour and in labour with variable decelerations

OBJECTIVE

To assess the distribution of fetal blood flow impedance of the umbilical and middle cerebral artery in active uncomplicated labour and in labour complicated by variable decelerations.

INTERVENTIONS

Blood flow impedance of the umbilical and fetal middle cerebral arteries was assessed by means of pulsed Doppler ultrasonography and measured by the resistance index (RI) and the systolic/diastolic ratio.

SUBJECTS

35 women at 38-40 weeks gestation admitted to, or monitored in the intrapartum unit. One group of 25 women had a normal active labour, the second group of 10 women were in active labour with moderate variable decelerations. A control group of 25 women--healthy pregnant women at term but not in active labour. All three groups were comparable for maternal age and parity.

SETTING

Hospital department of obstetrics and gynaecology, Israel.

DESIGN

A prospective descriptive study.

RESULTS

There was a 40% reduction in middle cerebral artery blood flow impedance in the two groups of women in active labour compared with the control group. Umbilical blood flow did not differ significantly between the three groups. Fetal middle cerebral blood flow impedance in labour was not significantly different in uncomplicated labours and those complicated by fetal heart rate decelerations.

CONCLUSIONS

During active labour, mechanisms that may be unrelated to low fetal blood oxygen content reduce fetal brain blood vessel impedance.