BLOOD-FLOW VELOCITY PROFILE IN THE FETAL AORTIC ISTHMUS - A SENSITIVEINDICATOR OF CHANGES IN SYSTEMIC PERIPHERAL RESISTANCES .2. PRELIMINARY CLINICAL OBSERVATIONS

Objective: Experimental studies have demonstrated that with a progress ive increase in resistance to placental blood flow, changes of diastol ic flow profile in the aortic isthmus precede those of the umbilical a rtery. The purpose of this study was to determine if the events observ ed in the aortic isthmus of exteriorized and anesthetized lamb fetuses could actually be observed in the human fetus. Methods: Five patients referred for suspicion of impaired umbilical circulation form the sam ple for this report. Their Doppler echocardiographic findings were com pared with normal fetuses of the same gestational age. Results: In the group of normal fetuses, a forward diastolic flow was always recorded in both the umbilical artery and the aortic isthmus. In the impaired umbilical circulation group, one subject had forward diastolic flow ve locities recorded in both extremities of the umbilical artery. In thre e other cases, forward diastolic flow velocities were observed at the placental end of the cord whereas no diastolic velocity could be recor ded at the abdominal end. In the last patient, no diastolic velocities were recorded either at the placental or the abdominal end of the cor d, or in the thoracic descending aorta. Reverse diastolic flow was obs erved in the aortic isthmus of all five patients. Conclusion: It is co ncluded that the aortic isthmus, due to its unique location in the fet al circulation, appears to be an ideal site for detection of changes i n flow velocities reflecting the balance between vascular resistances of the lower and upper body.