Flow studies in a model carotid bifurcation.

Abstract

Boundary layer separation in a plexiglass model carotid bifurcation was investigated in relation to the origin of atherosclerotic plaque clinically found in this region. Our model was comparable to a human carotid in both dimensions and geometry. T he predilection for atherosclerosis to occur at bifurcations in the arterial tree is well documented. 1 ' 2 This finding led to the hypothesis that hemodynamic factors are in some way involved in atherogenesis, although the precise nature of the flow or pressure changes favoring atherogenesis is not yet well understood. In humans, one of the most common sites for localization of atherosclerosis is at the carotid bifurcation, especially at the origin of the internal carotid artery where it may be the cause of transient ischemic attacks or stroke. model of the human carotid bifurcation based on averaged data from angiographic measurements. The flow field within this bifurcation model was studied with the laser Doppler anemometer under steady flow conditions, and velocity profiles across the bifurcation determined. 8 This work demonstrated a large region of flow separation and low wall shear stress at the origin of the internal carotid. In previous work from this laboratory, we have demonstrated the three-dimensional nature of separation and secondary flow in model anastomoses and bifurcations. 910The Balasubramanian model does not incorporate the curvature of vessels that is seen on arteriography. We have taken the internal measurements from Balasubramanian's model and have superimposed on that the curvature of vessels seen in the arteriogram of a carotid artery with atherosclerotic plaque present at the bifurcation (figure 1). This model is, therefore, a very close approximation of the carotid bifurcation seen in figure 1 prior to the formation of the atherosclerotic plaque. This allows us to demonstrate the flow field under steady and pulsatile flow conditions. The relevance of these studies to the formation of atherosclerotic plaque is also discussed.

Carotid bifurcation atherosclerosis. Quantitative correlation of plaque localization with flow velocity profiles and wall shear stress.

“…The separated flow zone does not appear to exist during the brief period of early systole in the model, for forward flow is observed throughout the sinus during this time. As the flow waveform reaches the decreasing velocity phase, however, separation occurs rapidly and its location migrates along the outer wall, becoming stable during diastole, hi a similar study, LoGerfo et al (1981), reported little qualitative difference in carotid bifurcation flow fields between steady and pulsatile flow. In a study of flow and plaque localization in a cast of a human aortic bifurcation, Friedman et al (1981), found a negative correlation between intimal thickness and wall shear rate.…”

Major carotid plaque surface irregularities correlate with neurologic symptoms

“…This predilection corresponds to the observed regions of low wall shear stress, flow separation, flow reversal, and helical flow in this location in models of the carotid bifurcation. [24][25][26] Indeed, in 78% of the severely atherosclerotic bifurcations in this study, the bulk of the plaque in the ICA arose from the NFDW. In these cases, the maximal stenosis was usually within 10 mm of the flow divider.…”

Flow separation in the renal arteries.

“…Flow separation throughout the entire cycle in their study occurred at flow ratios of 0.15 and 0.30 in models that simulate the aortic bifurcation. 18 LoGerfo et al, 19 using a model of the carotid bifurcation indicated that flow separation during steady flow occurred at a flow ratio of 0.28. Similar observations during pulsatile flow were also made by Ku and Giddens 20 using a model of the carotid bifurcation.…”