Figure 5.

Spectral representation of flow-velocities. Placing a volume sample in the vessel lumen as in the tributary artery of a radio cephalic AVF (a) or brachial artery (b) we can record a spectral Doppler trace. Velocities of RBCs, crossing the gate, are plotted versus time and represented as a velocity over time curve. The “y axis” represents velocity (m/sec) and “x axis” the time. Spectral curve provides a measurement of maximal and mean velocity enveloping the curve and integrating the velocities below the curve. Above the “zero line” the velocities are towards the transducer while below the “zero line” are away from the transducer.