Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI.
Section of Vascular Surgery, Department of Surgery, University of Michigan Health System, Ann Arbor, MI.
J Vasc Surg Venous Lymphat Disord. 2023 Sep;11(5):1023-1033.e5. doi: 10.1016/j.jvsv.2023.05.017. Epub 2023 Jun 22.
Elevated shear rates are known to play a role in arterial thrombosis; however, shear rates have not been thoroughly investigated in patients with iliac vein compression syndrome (IVCS) owing to imaging limitations and assumptions on the low shear nature of venous flows. This study was undertaken to develop a standardized protocol that quantifies IVCS shear rates and can aid in the diagnosis and treatment of patients with moderate yet symptomatic compression.
Study patients with and without IVCS had their iliac vein hemodynamics measured via duplex ultrasound (US) at two of the following three vessel locations: infrarenal inferior vena cava (IVC), right common iliac vein, and left common iliac vein, in addition to acquiring data at the right and left external iliac veins. US velocity spectra were multiplied by a weighted cross-sectional area calculated from US and computed tomography (CT) data to create flow waveforms. Flow waveforms were then scaled to enforce conservation of flow across the IVC and common iliac veins. A three-dimensional (3D), patient-specific model of the iliac vein anatomy was constructed from CT and US examination. Flow waveforms and the 3D model were used as a basis to run a computational fluid dynamics (CFD) simulation. Owing to collateral vessel flow and discrepancies between CT and US area measurements, flows in internal iliac veins and cross-sectional areas of the common iliac veins were calibrated iteratively against target common iliac flow. Simulation results on mean velocity were validated against US data at measurement locations. Simulation results were postprocessed to derive spatial and temporal values of quantities such as velocity and shear rate.
Using our modeling protocol, we were able to build CFD models of the iliac veins that matched common iliac flow splits within 2% and measured US velocities within 10%. Proof-of-concept analyses (1 subject, 1 control) have revealed that patients with IVCS may experience elevated shear rates in the compressed left common iliac vein, more typical of the arterial rather than the venous circulation. These results encourage us to extend this protocol to a larger group of patients with IVCS and controls.
We developed a protocol that obtains hemodynamic measurements of the IVC and iliac veins from US, creates patient-specific 3D reconstructions of the venous anatomy using CT and US examinations, and computes shear rates using calibrated CFD methods. Proof-of-concept results have indicated that patients with IVCS may experience elevated shear rates in the compressed left common iliac vein. Larger cohorts are needed to assess the relationship between venous compression and shear rates in patients with IVCS as compared with controls with noncompressed iliac veins. Further studies using this protocol may also give promising insights into whether or not to treat patients with moderate, yet symptomatic compression.
已知剪切率升高在动脉血栓形成中起作用；然而，由于成像限制和对静脉血流低剪切特性的假设，尚未对髂静脉压迫综合征（IVCS）患者的剪切率进行彻底研究。本研究旨在制定一种标准化方案，以量化 IVCS 的剪切率，并有助于诊断和治疗中度但有症状的压迫患者。
研究了患有和不患有 IVCS 的患者，通过双功超声（US）在以下三个血管位置中的两个位置测量其髂静脉血流动力学：肾下腔静脉（IVC）下腔静脉、右髂总静脉和左髂总静脉，以及获取右髂外静脉和左髂外静脉的数据。US 速度谱乘以从 US 和计算机断层扫描（CT）数据计算的加权横截面积，以创建血流波形。然后将血流波形缩放，以确保在 IVC 和髂总静脉中保持流量守恒。从 CT 和 US 检查构建髂静脉解剖的三维（3D）患者特定模型。使用血流波形和 3D 模型作为基础，运行计算流体动力学（CFD）模拟。由于侧支血管血流和 CT 与 US 面积测量之间的差异，内部髂静脉的流量和髂总静脉的横截面积被迭代地校准，以与目标髂总流量相对应。模拟结果与测量位置的 US 数据进行了比较。对模拟结果进行后处理，以得出速度和剪切率等数量的空间和时间值。
使用我们的建模方案，我们能够构建髂静脉的 CFD 模型，该模型与髂总血流分流的吻合度在 2%以内，与 US 测量速度的吻合度在 10%以内。初步分析（1 名患者，1 名对照）表明，IVCS 患者的受压左髂总静脉可能会经历升高的剪切率，更类似于动脉而不是静脉循环。这些结果鼓励我们将该方案扩展到更大的 IVCS 患者和对照组患者中。
我们开发了一种方案，该方案从 US 获得 IVC 和髂静脉的血流动力学测量值，使用 CT 和 US 检查创建静脉解剖的患者特定 3D 重建，并使用经过校准的 CFD 方法计算剪切率。初步结果表明，IVCS 患者的受压左髂总静脉可能会经历升高的剪切率。需要更大的队列来评估 IVCS 患者与非受压髂静脉的对照组之间静脉压迫与剪切率之间的关系。使用该方案的进一步研究也可能为中度但有症状的压迫患者是否需要治疗提供有希望的见解。
