Figure 5:

The predicted relationship between radial artery radius and uterine artery velocity waveforms, with normal spiral artery resistance. Panel A shows the dicrotic notch height, normalized by total height of the velocity waveform and Panel B shows the predicted ratio of systolic (S) to diastolic (D) flow velocity, S/D, resistance index, RI and pulsatility index, PI. There is little impact of radial artery caliber on velocity waveforms over much of the physiological range of radius. However, at radii representative of pre-eclamptic radial arteries, or radial arteries in early pregnancy small changes in radial artery size can result in large changes in uterine artery velocity waveforms.