Biological flows vary throughout the cardiac cycle. The analog output can be filtered to give a pulsatile flow or mean flow signal.

The velocity of flowing blood is usually measured in cm/s. It is always zero at the vessel wall and the velocity profile across a vessel can have various shapes depending upon the type of flow being observed (see also pulsatile flow). Laminar flow giving rise to a laminar velocity profile, plug flow giving rise to a flat velocity profile and disturbed flow can be distinguished.
Normal peak systolic velocities in the femoral and popliteal arteries vary from 90 to 110 cm/s in the femoral artery and from 40 to 70 cm/s in the popliteal artery.

See also Bi-directional Flow, Pulsatility Index, and Acceleration Index.

(PI) The pulsatility index quantifies the shape of the blood velocity waveform by the ratio of the flow volume amplitude and mean flow volume.

See also Pulsatile Flow.