In duplex assessment, how does normal flow in the portal vein appear?

In duplex assessment, the normal flow in the portal vein is characterized as phasic with respiration. This is due to the influence of respiratory movements on the pressure in the thoracic cavity, which affects venous return and the flow dynamics in adjacent venous structures.

As the diaphragm moves during inhalation and exhalation, it creates pressure variations that lead to changes in blood flow patterns. In the case of the portal vein, this results in a phasic waveform that reflects these respiratory changes. The flow pattern can be seen as alternating between slightly elevated flow during inhalation and a decrease during exhalation, demonstrating the impact of respiratory cycles on venous return.

Other flow characteristics such as pulsatile or continuous are not typical for the portal vein under normal physiological conditions. A pulsatile flow is often associated with arterial structures or certain pathological conditions, while a continuous flow would not reflect the normal physiological influence of respiration on venous blood flow in the portal system. Steady-state flow does not accurately depict the variations expected in the portal vein due to respiratory cycles.