The interpretation of uterine artery pulsatility index in normal and hypertensive pregnancy

The Doppler flow velocity pulsatility index (PI) of the uteroplacental vascular bed is of debatable value for the interpretation of hemodynamic changes, when these are due both to pathological alterations in the vasculature, as in mild pre-eclampsia, and to physiological adjustments to vasoactive substances. The aim of this study was to apply a mathematical model, which includes maternal pulse pressure and mean arterial pressure, to the PI and to investigate whether this formula would add information with respect to discrimination between normal women and those with mild or severe pre-eclampsia. The subjects were patients with mild (n = 41) and severe (n = 34) pre-eclampsia and, as a control group, healthy pregnant women (n = 46). The uterine artery PI was studied by spectral Doppler analyses and compared to a P(z) value, theoretically representing a 'back pressure' in the uteroplacental circulation. Additionally, P(z) values were computed from earlier data concerning the dynamic circulatory effects of dihydralazine and acute volume expansion. The basal PI was significantly higher in the severely pre-eclamptic patients but not in the mildly pre-eclamptic patients compared to the controls. However, the P(z) was significantly higher in patients with both mild (p < 0.001) and severe pre-eclampsia (p < 0.0001) compared to the normal group. In the severely pre-eclamptic patients receiving dihydralazine, the P(z) tended to decrease (p = 0.07), in contrast to the volume-expansion group where P(z) was unaffected by the procedure. In conclusion, it seems that including measurement of the mean arterial pressure and pulse pressure with the PI adds valuable information about the circulatory status in this particular vasculature, regarding both 'basal' values and hemodynamic changes.