What does a spectral tracing indicate if it is above the axis?

A spectral tracing that appears above the baseline axis indicates a positive shift in flow direction. This is based on the principles of Doppler ultrasound, where the frequency of the reflected sound waves shifts depending on the movement of the blood cells in the direction of the ultrasound beam.

When blood flows toward the transducer, the frequency of the sound waves increases, resulting in a positive shift that is represented above the baseline on the spectral waveform. This positive spectral shift reflects factors such as increased velocity of blood flow toward the probe and can provide valuable information for assessing conditions related to vascular health.

In contrast, a shift below the axis would indicate a negative shift, representing flow moving away from the transducer. Understanding the implications of these shifts is crucial for interpreting Doppler ultrasound results in the context of phlebology and vascular diagnostics.