The waveforms seen in the Doppler tracing of the hepatic veins are primarily derived from which physiological phase?

The waveforms seen in the Doppler tracing of the hepatic veins primarily represent the phase of passive venous return. In this context, the Doppler waveform reflects the normal flow patterns of blood returning to the heart from the liver through the hepatic veins, which is influenced significantly by the pressure changes within the right atrium during the cardiac cycle.

During diastole, when the ventricles are relaxed, blood passively returns from the hepatic veins into the right atrium due to the pressure differential. This predominantly passive flow is characterized by a continuous flow pattern observed in the Doppler tracing, indicating that blood moves into the heart without the additional force from atrial contraction.

In the other phases, such as ventricular contraction or atrial systole, the flow dynamics differ significantly. Ventricular contraction pushes blood out of the heart, not creating a passive return flow from the hepatic veins. Atrial systole contributes to the movement of blood, but in the context of hepatic venous flow, it is less dominant than the passive flow. Active ventricular filling relates to the moment when the ventricles actively fill with blood, but this does not significantly affect the hepatic venous return tracing. Thus, the Doppler tracing is best characterized as resulting primarily from