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Normal blood flow in the arteries of the lower limb
Last reviewed: 04.07.2025
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Picture of normal blood flow at rest
After identifying vessels in B-mode, examine them in color duplex sonography in the longitudinal axis and, if necessary, in the transverse axis. Color mode is initially used only in the leg and forearm region, as it allows the localization and course of vessels to be determined. Adjust the pulse repetition rate before measuring blood flow velocity. For longitudinal scanning, vary the beam and select the transducer angle to improve the beam-vessel angle and optimize the color image. Due to high peripheral resistance, spectra from peripheral arteries show a typical triphasic flow pattern consisting of a steep systolic rise , a systolic peak, a reverse flow component (“dip”) in early diastole, forward flow in late diastole, and presystolic zero flow. Note the typical constant flow in the homonymous vein at each stage of the cardiac cycle.
Picture of normal blood flow during physical activity
Exercise reduces peripheral resistance, which normally results in a biphasic spectrum that differs from the resting spectrum by the absence of backflow in early diastole, higher diastolic flow, and higher peak systolic velocity. Exercise may involve repeated hand squeezes or foot circles.
The wall filter should be 100 Hz or lower and the sample volume should be no more than 2/3 of the vessel lumen to avoid wall artifacts. An empty spectral window) under the systolic peak is normal and indicates the absence of slow turbulent flow components. When stenosis occurs, the window is filled. Stenosis can be quantified by analyzing the spectral waveforms that determine the ratio of peak flow velocities or planimetrically on true transverse images. The transverse region must be reduced by at least 30% to determine detectable spectral changes. Pulsatility and resistance indices provide little information because they vary with vascular resistance (eg, the pulsatility index can vary from 3 to 30). Flow velocities also vary, but peak systolic velocity should be approximately 100 cm/s in the thigh and 50 cm/s in the calf.
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