Pulsatility index and its relationship to placental vascular resistance during partial umbilical venous occlusion: a study in fetal lambs.
To study the effect of partial occlusion of the umbilical vein upon umbilical artery velocity waveforms, 4 chronically instrumented pregnant sheep have been subjected to measurement of the relevant haemodynamic parameters, i.e. the arterial inflow pressure, placental venous outflow pressure (Pv), venous blood flow (Quv) and arterial blood velocity waveform. The pulsatility index (PI) of the velocity waveform increases significantly for a Quv reduction of 40% or more (p less than 0.05). The Quv correlates well with the PI (r = 0.61) and the Pv (r = 0.71). The correlation between fetal heart rate (FHR) and Quv, FHR and PI is 0.75 and 0.64, respectively. The placental vascular resistance (R) can be calculated using the Poiseuille equation. There is not significant correlation between R and PI. It can be concluded that the increase in PI in the umbilical artery during partial venous occlusion is very likely caused by an increased Pv rather than a change in R.
van Vugt
J M
JM
Department of Obstetrics and Gynecology, Academic Hospital Maastricht, The Netherlands.
Hasaart
T H
TH
Ruissen
C J
CJ
Hoogland
H J
HJ
Hoeks
A P
AP
de Haan
J
J
D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D005260:Female; D006340:Heart Rate, Fetal; D006439:Hemodynamics; D010920:Placenta / Q000098:blood supply*; D011247:Pregnancy; D012756:Sheep; D014469:Umbilical Arteries / Q000502:physiology*; D014471:Umbilical Veins / Q000502:physiology*; D014655:Vascular Resistance