Journal of Ultrasound in Medicine, Vol 10, Issue 12 671-675, Copyright © 1991 by American Institute of Ultrasound in Medicine
Influence of the measurement location on the resistance index in the umbilical arteries: a hemodynamic approach
P. Vieyres, A. Durand, F. Patat, P. Descamps, J. M. Gregoire, D. Pourcelot and L. Pourcelot
Biomedical Engineering and Science Institute, Drexel University, Philadelphia, Pennsylvania 19104.
A computer model was used to study the primary factors generating the
reduction in resistance index, (S-D)/S, values observed by ultrasonic
Doppler measurements in the umbilical artery, from the fetal insertion to
the placental insertion (S represents the amplitude of the systolic peak
and D the amplitude of the diastolic peak). This hemodynamic approach shows
that the placental resistance is the primary factor, the viscosity and the
cord length playing secondary roles. Clinically, the position of the
measurement along the cord is an important factor. To increase the
sensitivity of the index, the Doppler measurement must be performed near
the fetal insertion, whereas a measurement near the placental insertion
will make the Doppler examination more specific.
