Normal spectral waveforms in the superior mesenteric artery. (a) Fasting waveform from a 26-day-old neonate shows a high-resistance flow pattern. (b) Postprandial waveform from a 6-day-old neonate shows a low-resistance pattern with an increase in diastolic flow velocity.

The celiac artery has a high-resistance pattern at its origin, with a small amount of reversed flow in early diastole. Its distal portion and branches lose the reversed early-diastolic flow component, showing continuous low-resistance forward flow throughout the cardiac cycle .

With the body in a fasting state, flow through the superior mesenteric artery has a high-resistance pattern, with a small amount of reversed flow in early diastole (Fig a). After a meal, the PSV and diastolic velocities increase. The reversed diastolic flow disappears, a low-resistance pattern develops, and the systolic spectral peak broadens (Fig b).

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