Fig. 2. Representative example of uterine artery velocity waveform in a single parturient at baseline (A  and B ) and after 18 mg ephedrine (C  and D ) in the absence of uterine contraction (A  and C ) and at the peak amplitude of uterine contraction (B  and D ). Arrows indicate peak systolic (V^sys) and end-diastolic (V^dia) flow velocities in the uterine artery. (B ) Dramatic reduction in V^diaduring contraction. (D ) Complete restoration after administration of intravenous ephedrine. Note that scaling is different among panels. RI = resistance index.