Normal Doppler spectrum from the upper abdominal aorta in a 10-year-old boy shows a typical waveform characterized by a sharp increase in antegrade flow velocity during systole, followed by a reversal of flow in early diastole and then low-velocity antegrade flow in the remainder of diastole.

The normal Doppler flow pattern in the aorta is that of plug flow. In the aorta and iliac arteries, the flow is typically high resistance, with a sharp increase in antegrade flow velocity during systole followed by a rapid decrease that bottoms out in early diastole with a brief period of reversed flow (Fig 13). Low-velocity antegrade flow then resumes and continues for the remainder of diastole. Spectral Doppler analysis shows that the peak antegrade velocity decreases and the amount of retrograde flow increases as the flow progresses from the proximal aorta to the iliac vessels (17).


http://radiographics.rsna.org/content/28/3/691.full