Which change of the inferior vena cava spectral Doppler waveform is expected superior to a...

In the presence of a nonocclusive thrombus, Doppler waveform above the thrombus typically shows dampened flow with loss of normal respiratory phasicity due to partial venous outflow obstruction. Complete absence of flow is typically seen with occlusive thrombus.

According to Zwiebel’s Introduction to Vascular Ultrasound:

“Partial obstruction produces dampened and continuous flow patterns superior to a nonocclusive thrombus.”