Tortuosity of the superficial femoral artery and its influence on blood flow patterns and risk of atherosclerosis

The superficial femoral artery (SFA) is a typical atherosclerosis-prone site. We aimed to explore whether the tortuosity of the SFA associates with the occurrence of atherosclerosis and investigate how vascular tortuosity influences the characteristics of blood flow. Ten patients diagnosed with atherosclerotic disease in their SFAs while free of systemic atherosclerosis risk factors were enrolled together with ten atherosclerosis-free patients. The tortuosity of each SFA was quantitatively evaluated by calculating the averaged curvature (AC), maximum curvature (MC) and fraction of high curvature (FC) based on the geometrical model reconstructed from medical images. Hemodynamic studies were performed using both geometrically simplified and anatomically realistic models of the SFA to systematically address the hemodynamic effects of vascular tortuosity. Morphological analyses revealed that all curvature indices of the SFA were significantly larger in patients with atherosclerosis than in atherosclerosis-free patients (AC [mm−1]: 0.034 ± 0.016 vs. 0.018 ± 0.006; MC [mm−1]: 0.055 ± 0.023 vs. 0.034 ± 0.008; FC [%]: 22.77 ± 10.22 vs. 11.39 ± 6.82; p < 0.001). Simulations of blood flows in the geometrically simplified SFAs showed that increasing vascular curvature caused a progressive increase in the area ratios of low wall shear stress (LWSA) and high oscillatory shear index (HOSA). Hemodynamic studies on the anatomically realistic SFAs further demonstrated that high-curvature SFAs (n = 10) had overall larger LWSA and HOSA compared with low-curvature SFAs (n = 10) (LWSA [%]: 4.13 ± 1.91 vs. 1.79 ± 1.13, p = 0.009; HOSA [%]: 4.95 ± 1.92 vs. 2.37 ± 1.51, p = 0.007). These results suggest that increased vascular tortuosity augments the severity and distribution of atherosclerosis-promoting flow disturbances in the SFA and may be an independent risk factor for atherosclerosis.