Factors determining aortic and umbilical blood flow pulsatility in fetal sheep

Assessment of umbilical arterial and venous flow using color Doppler

“…Neither index was designed for use in obstetrics; the pulsatility index was developed to evaluate proximal changes in resistance as a result of stenosis 11 and the resistance index to examine changes distal to the common carotid artery 12 . These indices have limited sensitivity to moderate changes in distal resistance in low-impedance vascular beds; large changes in vascular resistance may not be reflected by changes in the pulsatility index 13,14 . The complex relationship between input pressure pulsatility, impedance and distal resistance produces changes that defy simple analysis of the umbilical artery flow velocity waveform.…”

Endothelial dysfunction: comparative evaluation of ultrasound dopplerography, laser dopplerflowmetry and direct monitoring of arterial pressure for conducting pharmacological tests in rats

“…After systemic administration of vasodilators, the volume of circulating blood is redistributed towards the microcirculatory bloodstream. These processes lead to a decrease in diastolic velocity and an increase in the amplitude of the peaks of the blood flow velocity curve, which causes an increase in both indices, despite a reduced vascular resistance (Adamson and Langille 1992).…”

“…In most cases, these indices adequately reflect the patency of the vascular network distal to the point of registration. However, some authors emphasise that their sensitivity varies depending on the study design and is applicable only to a limited range of models (Adamson and Langille 1992).…”

Intraplacental Spectral Doppler Scanning: Fetal Growth Classification Based on Doppler Velocimetry

“…More clinical data are required in order to support our suggestion, and in order to establish our method as a clini cal tool. 18 Gynecol Obstet Invest 1997:43:11-19 H a b c rm a n /F ric d m a n…”

“…This has been related to the increase in the number of arterial small ves sels within the placenta, resulting in decreased down stream impedance. The relationship between obliteration of intraplacental small arterial vessels and Doppler in dices, and between increased placental resistance and increased indices, has been confirmed in a scries of exper iments in sheep, where conditions simulating higher pe ripheral resistance were reproduced through progressive embolization of the umbilical placental circulation [3][4][5][15][16][17][18], Umbilical artery blood flow velocimetry mea surements have been recommended as a tool for antenatal decision making and have been proved to be beneficial for fetal surveillance in the high-risk population [19][20][21][22][23]. However, no advantage was found when umbilical artery Doppler was used as a screening test in the low-risk popu lation [24], The low efficacy of UA Doppler velocimetry as a diagnostic tool to predict placental disease, especially in a low-risk population, could probably be explained by the fact that these indices reflect both the overall function al size of the placental bed, as well as the level of oblitera tion of terminal arterial vessels.…”