In vitro Vergleich des Strömungsgeschwindigkeitsfeldes in termino-lateralen Anastomosen
Introduction: The prognosis of prosthetic femorodistal bypass grafts is limited, mainly due to the formation of myointimal hyperplasia (MIH). Local hemodynamics within the distal end-to-side anastomosis (ESA), in particular the flow velocity field, is known to strongly influence MIH. Near-wall low shear stress, low flow velocity (LV), stagnation and recirculation (RC) due to flow separation (FS) are precipitating factors for MIH. An optimal anastomotic geometry should minimize zones of LV, RC, and FS and thus MIH within the ESA. Methods: Silicone life-size models of 8 ESA with different geometries were perfused with a blood-analog fluid in a specifically designed flow rig, simulating physiological conditions (pulsatile flow, Wormersley’s α-parameter 4.13, mean Reynolds’ number Re 321, variable flow split of 1:2,1:1,2:1). High-resolution color-coded Doppler sonography (CDS) was employed to visualize flow patterns in the plane of symmetry of the anastomosis. Still video analysis was performed for maximal systole and beginning of diastole. Quantification was achieved by calculating the relative area containing LV, RC, and FS for each anastomosis. Statistical analysis (SPSS software) employed Student‘s t-test for significance of differences between the means of relative area. Results: CDS enabled accurate and quantitative analysis of the flow velocity field within the anastomotic site. Areas containing LV, RC, and FS were clearly identified. The relative areas of LV, RC, and FS were dependent on anastomotic geometry, flow split, and time of the pulsatile cycle. With few exceptions, there were highly significant differences between all anastomotic shapes. Conclusions: CDS is an adequate method not only to visualize but also to quantitatively analyze local hemodynamics in ESA. The strong influence of anastomotic geometry on MIH-associated flow patterns was independent from flow split and time of the pulsatile cycle. Our experimental setting allows to identify an optimal anastomotic design.
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