Page 65 - Libro vascular I
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PERIPHERAL VASCULAR ULTRASOUND
Vein
ICA
B
CCA
A
A
B
C
flow at rest (A) and monophasic hyperemic flow following exercise (B). Low volume monophasic flow seen in the foot distal to an occlusion (C).
also due to distal vasodilatation, in an attempt to maximize flow distal to the diseased vessel, but this can usually be distinguished from hyperemic flow as the velocity of the flow is low and the
A: Color flow image showing reverse flow in the origin of a normal internal carotid artery.
B: Spectral Doppler waveform obtained from the area of flow separation shown by the arrow in A.
Figure 5.12
systolic rise time may be longer. The systolic rise time is the time between the beginning of systole and peak systole.
Flow at bifurcations and branches
The arterial tree divides many times, and each branch will affect the velocity profiles seen. The hemodynamics of the carotid bifurcation has been extensively investigated using multigate pulsed Doppler systems, and more recently using color Doppler systems, and these investigations show that localized reversed flow is seen at the carotid bifurcation in normal subjects. Figure 5.12A shows reversal of flow, due to flow separation, at the origin of a healthy internal carotid artery. The schematic diagram in Figure 5.13 indicates how the asymmetric flow profile in a normal proximal internal carotid artery develops, with the high- velocity flow occurring toward the flow divider and the reverse flow occurring near the wall away from the origin of the external carotid artery. The effect is primarily due to a combination of the pulsatile flow, the relative dimensions of the vessels, the angle of the bifurcation and the curvature of the vessel walls, making it difficult to predict these profiles. Figure 5.12B is a spectral Doppler signal obtained from the area of flow separation shown by an arrow in Figure 5.12A, illustrating reverse flow during
Doppler spectra obtained from a normal dorsalis pedis artery in the foot showing bi-directional
Figure 5.11
