Normal flow in hepatic veins

What is the normal spectral Doppler waveform of hepatic veins?

Here's what I observed on Doppler trace of the right and left hepatic veins. 

There are broadly 4 waves in a hepatic vein on spectral Doppler tracing. A, S, V and D waves. 

Here's a brief description:

A wave: The A wave is the first negative wave in the hepatic vein spectral Doppler waveform. It represents the brief period of increased resistance to blood flow caused by atrial contraction. The A wave is usually smaller and less prominent than the S and D waves.

S wave: The S wave is the first positive wave in the hepatic vein spectral Doppler waveform. It is caused by the initial surge of blood flow into the hepatic vein during the systolic phase of ventricular contraction. The S wave is usually sharp and well-defined.

V wave: The V wave is the second negative wave in the hepatic vein spectral Doppler waveform. It represents the early diastolic phase, during which the ventricles relax and blood flow decreases. The V wave is usually lower in amplitude and longer in duration than the A wave.

D wave: The D wave is the second positive wave in the hepatic vein spectral Doppler waveform. It represents the passive filling of the hepatic vein during the late diastolic phase, when the atria contract and push blood into the ventricles. The D wave is usually broader and less steep than the S wave.

Summary:

In a normal hepatic vein spectral Doppler waveform, these four waves form a triphasic pattern with three peaks (S, D, and V) and two troughs (A and V), reflecting the phases of the cardiac cycle and blood flow dynamics in the liver. However, the waveform can be affected by various factors such as age, sex, body position, and cardiac function. Therefore, it is important to interpret the waveform in the context of the patient's clinical history and other imaging findings.

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Doppler ultrasound hepatic vein