Hemodynamics of femoropopliteal arteries in straight and bent limb postures

Peripheral artery disease (PAD) is a condition primarily affecting the arteries of the legs. It is most commonly caused by atherosclerosis, which leads to partial or complete obstruction of blood vessels. This reduced blood flow results in insufficient oxygen supply to downstream tissues, often causing leg muscle pain and, in severe cases, leading to gangrene and potential amputation of the lower limbs. The morphological characteristics and stability of atherosclerotic plaques vary throughout the vascular tree. The distal superficial femoral artery (SFA) at the adductor hiatus (AH) and the popliteal artery (PA) behind the knee are common sites of atherosclerosis. These regions undergo significant deformation during limb flexion, promoting vascular injury, cellular proliferation, and disease progression, and resulting in tortuous segments with complex flow dynamics. Computational fluid dynamics (CFD) simulations are effective for analyzing hemodynamic changes induced by limb flexion-related deformations. In this context, the aim of this study was to characterize altered flow patterns in femoropopliteal arteries at various limb positions by quantifying hemodynamic descriptors associated with plaque formation. A total of 111 unsteady CFD simulations were performed on femoropopliteal arteries from 15 cadavers in straight, walking, sitting, and fetal limb positions. Various flow rates corresponding to different flexion angles were applied. Vessel geometries were reconstructed from centerline coordinates and diameters, and simulations were conducted without accounting for the effects of side branches. The results showed that regions with low time-averaged wall shear stress (TAWSS) were primarily located in the proximal SFA, as well as in the AH and PA, where significant changes in curvature occur. Analysis of the Oscillatory Shear Index (OSI), transverse wall shear stress (transWSS), and cross flow index (CFI) revealed that flow in the femoropopliteal artery (FPA) is predominantly oscillatory rather than multidirectional. Additionally, a correlation between helical flow and plaque-prone regions was identified, with affected zones aligning with observations from experimental studies. A secondary analysis evaluated the effects of flow rate, tapering, curvature, and tortuosity. As blood flows distally through the artery, hemodynamic descriptors increased, primarily influenced by tapering, with curvature and tortuosity contributing to a more widespread distribution of values. Additionally, higher flow rates resulted in increased absolute values of hemodynamic descriptors. In conclusion, this study highlights the significance of patient-specific simulations in PAD research and advocates for the use of CFD as a tool to predict atherosclerotic plaque progression and localization.