Biomedical Engineering Reference
In-Depth Information
If the boundary layer of either type of flow separates from the wall, there is a zone of stagnant
fluid. For blood, this would be a zone where thrombosis (clotting) would occur. Such a clot might
become dislodged, where it would be transported downstream to lodge in a smaller blood ves-
sel. This might result in a stroke if the dislodged clot (called an embolism) were to become
trapped in the cerebral (brain) circulation. Such boundary layer separation might occur at sharp
bends where the fluid flow cannot adequately follow the curvature (Figure 14.37). Boundary
layer separation might also occur at branches of blood vessels as shown in Figure 14.38.
There is certainly a danger in boundary layer separation owing to the potential for blood
clotting. Separation also occurs downstream of an atherosclerotic plaque that adheres to the
vessel wall and narrows the vessel diameter. As the diameter becomes smaller with growth
of the plaque, there is separation downstream of the stenosis (narrowing of the vessel),
which creates clotting and further promotes the stenosis downstream. Thus, at some point
in the progression of arterial disease, there is a tipping point where the stenosis becomes
FIGURE 14.37
Boundary layer separation at a tight curve, such as the aortic arch.
FIGURE 14.38
Boundary layer separation in branching blood vessels.
