Rest and Exercise Hemodynamics in AAA Progression

这个项目的目标是量化运动对血液动力学状况的急性和慢性影响 在患有小AAA（AAA直径等于或> 3，等于或< 5 cm）的人类受试者的肾下主动脉中。受试者将是项目IV的具体目标2：小型AAA运动疗法的评价中所述的标准治疗组和运动干预组的患者子集。我们将检验以下假设：（i）形状问题：作用在血管壁上的剪切力和动态张力的差异，由以下因素的差异引起： 动脉瘤形状，是AAA生长速度的预测因素，（ii）尺寸问题：随着AAA扩大，不良血流动力学 条件（包括低平均壁剪切应力和高颗粒停留时间的区域）恶化 在静止条件下，（iii）结构和运动物质：壁厚度，组织组成， 周期性室壁运动和流体-固体相互作用影响AAA扩大，（iv）运动事项：增加 急性下肢运动引起的肾下血流，消除了不良血流动力学区域 条件下，在所有受试者中显著增加壁面剪切应力并减少颗粒停留时间 无论AAA的形状或大小，（v）坚持很重要：定期锻炼会减缓AAA的进展， 尺寸和形状，并导致更有利的血液动力学和血管壁运动。我们将测试这些 通过量化静息和运动条件下的血流动力学和壁张应力， 小AAA患者的腹主动脉随机接受慢性运动疗法或标准疗法。 我们的具体目标是：（1）量化AAA患者中随时间变化的腹主动脉解剖结构，（2）量化 使用0.5T定制MR兼容自行车在静息和动态运动期间测量腹主动脉血流 开放式MRI，以及（3）开发和验证计算方法，以模拟血流、压力和壁 小AAA患者腹主动脉“患者特定”计算模型中的运动 随机分为慢性运动疗法组和标准疗法组。

The goal of this project is to quantify the acute and chronic effects of exercise on hemodynamic conditions in the infrarenal aorta of human subjects with small AAA (AAA diameter equal to or > 3, equal to or < 5 cm). The subjects will be a subset of the patients in the standard therapy arm and exercise intervention arm described in Specific Aim 2 of Project IV: Evaluation of Exercise Therapy for Small AAA. We will test the hypotheses that: (i) Shape matters: Differences in shear and dynamic tensile forces acting on the vessel wall, resulting from differences in aneurysm shape, are predictive of AAA growth rate, (ii) Size matters: As AAA enlarge, adverse hemodynamic conditions (including regions of low mean wall shear stress and high particle residence time) are exacerbated under resting conditions, (iii) Structure and motion matter: Differences in wall thickness, tissue composition, cyclic wall motion, and fluid-solid interactions affect AAA enlargement, (iv) Exercise matters: Increased infrarenal blood flow resulting from acute lower limb exercise, eliminates regions of adverse hemodynamic conditions, dramatically increasing wall shear stress and reducing particle residence time in all subjects regardless of AAA shape or size, (v) Persistence matters: Regular exercise slows AAA progression affecting size and shape, and results in more favorable hemodynamics and vessel wall motion. We will test these hypotheses by quantifying hemodynamics and wall tensile stresses under resting and exercise conditions in the abdominal aorta of patients with small AAA randomized to chronic exercise therapy or standard therapy. Our specific aims are: (1) Quantify time-varying abdominal aortic anatomy in AAA patients, (2) Quantify abdominal aortic blood flow at rest and during dynamic exercise using a custom MR-compatible bike in a 0.5T open MRI, and (3) Develop and validate computational methods to model blood flow, pressure, and wall motion in "patient-specific" computational models of the abdominal aorta of patients with small AAA randomized to chronic exercise therapy or standard therapy.