What does it mean if flow is found below the axis in spectral Doppler tracing?

In spectral Doppler tracing, the location of the flow relative to the baseline is crucial for interpreting the direction of the blood flow. When flow is detected below the baseline or axis, this is indicative of a negative shift. This means that the blood is flowing towards the transducer, which is represented by a downward deflection on the spectral Doppler graph.

This negative shift is an essential aspect of analyzing venous and arterial flow patterns, allowing sonographers to determine the direction and quality of blood flow in the vessels being examined. It is particularly useful in assessing conditions such as venous reflux, where blood may flow in the opposite direction from what is physiologically normal.

Understanding the concept of negative and positive shifts helps sonographers accurately interpret the Doppler waveforms, leading to informed clinical decisions regarding patient diagnosis and treatment plans.