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。 肾下主动脉小腹主动脉(腹主动脉直径等于或等于&t；3，等于或等于-lt；5厘米)。受试者将是在项目IV的特定目标2：评估小型AAA的运动疗法中描述的标准治疗组和运动干预组的患者的子集。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拉力的差异，由不同的 动脉瘤的形状，可以预测AAA的增长率，(Ii)大小重要：随着AAA的增大，血液动力学不良 条件(包括低平均壁面剪应力和高颗粒停留时间的区域)加剧 在静止条件下，(Iii)结构和运动物质：壁厚、组织成分、 循环室壁运动和流固相互作用影响AAA扩大，(Iv)运动事项：增加 急性下肢运动引起的肾下血流量，消除了不利的血液动力学区域 在所有受试者中，显著增加壁面剪应力并减少颗粒滞留时间 不论AAA的形状或大小，(V)坚持性很重要：定期锻炼减缓AAA的进展，影响 大小和形状，并导致更有利的血流动力学和血管壁运动。我们将测试这些 静息和运动条件下血流动力学和室壁拉应力的量化假说 小腹主动脉曲张患者随机分为慢性运动疗法和标准疗法。 我们的具体目标是：(1)量化腹主动脉患者的时变腹主动脉解剖；(2)量化 在0.5T中使用定制的MR兼容自行车在休息和动态运动时腹主动脉血流 开放式核磁共振，以及(3)开发和验证计算方法来模拟血流、压力和壁厚 小腹主动脉患者腹主动脉“患者特有”计算模型中的运动 随机分为慢性运动疗法或标准疗法。

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.