Mechanical Aspects of Pulsatile Blood Flow

人们普遍认为血液是生命的本质，但事实上，生命的本质不是血液，而是血液的流动。当心脏停止跳动时，身体不是因为缺乏血液而是因为缺乏血液流动而死亡。这个提议是关于血液流动的。*心血管系统内的血液流动是一个高度复杂的动力系统，由无数的管道和管道连接组成。这一建议的基础是，对这一复杂系统的全面理解在于力学领域，而不是医学领域。******血液流动有两个方面是属于力学领域的：(1)血液流动的脉动性赋予了系统一个动态维度，超越了常见的“管道”血液流动的观点，在这种观点中，血液流动的中断只被视为血管闭塞。这是对脉动性血流的不完整看法，因为它忽略了血流的振荡动力学。(2)虽然“血流”本身是由物理定律控制的，但心血管系统内的血流也受到神经血管的控制，这种控制源于身体不同区域对血液供应的需求，并由大脑的控制中心进行调节。这些系统协同工作的方式还没有被完全理解，而且，这个主题完全属于力学领域。*******本提案的重点是在三个特定器官的血流动力学方面的研究：大脑，心脏和子宫。每个系统都有其独特的机械问题，如下所述。*在大脑中，搏动的血液流动发生在刚性头骨的范围内。因此，压力和血流之间的关系不同于心血管系统的其他部位，目前还不完全清楚。我们正在寻求一种方法，允许对这种关系进行无创研究，目的是更好地理解脑血流量的机制。*在心脏中，心肌的灌注对心脏的正常功能至关重要，而心肌承担了大量的泵送作用。心肌的脉管系统如何在心肌的不同深度达到所需的连续和合理均匀的灌注，目前尚不清楚。我们正在使用显微ct成像和血管树跟踪技术相结合来研究心脏肌肉血液供应的流体动力学基础。*子宫的血液供应结合了心血管系统中血管结构和血管控制机制的一些最复杂的元素。这个系统的一个独特的特点是一组螺旋动脉，在正常怀孕的过程中，它们的几何形状和机械性能经历了复杂的转变。迄今为止，控制该系统功能设计的流体动力学原理，特别是在脉动流动条件下，尚未完全了解。对血管结构和相关控制机制的主要研究是该提议的一部分。******

Blood is widely considered as the very essence of life, yet, in fact, the essence of life is not blood but blood flow. When the heart stops beating, the body dies not because of lack of blood but because of lack of blood flow. This proposal is about blood flow.*Blood flow within the cardiovascular system is a highly complex dynamical system consisting of a myriad of tubes and tube junctions. The basis of this proposal is that a full understanding of this complex system lies in the realm of Mechanics, not Medicine. ****** There are two aspects of blood flow that reside decidedly in the realm of Mechanics: (1) The pulsatile nature of the flow gives the system a dynamical dimension beyond the common “plumbing” view of blood flow where disruptions in blood flow are seen in terms of only blood vessel occlusions. This is an incomplete view of pulsatile blood flow because it ignores the oscillatory dynamics of the flow. (2) While “flow” as such is controlled by the laws of physics, blood flow within the cardiovascular system is subject also to neurovascular control originating in demands for blood supply from different regions of the body and mediated by control centers in the brain. The way these systems work together is not fully understood and, again, the subject lies fully in the realm of Mechanics.******* The focus of this proposal is on a study of these dynamical aspects of blood flow in three specific organs: the brain, the heart, and the uterus. There are unique mechanical issues that are specific to each, as described briefly below.*In the brain, pulsatile blood flow takes place within the confines of a rigid skull. As a result, the relationship between pressure and flow is different from that elsewhere in the cardiovascular system and is currently not fully known. We are pursuing methodologies that allow a noninvasive study of that relationship, with the aim of establishing a better understanding of the mechanics of cerebral blood flow.*In the heart, perfusion of the heart muscle which does much of pumping action is critical to normal heart function. It is not known how the vasculature of the heart muscle achieves the required continuous and reasonably uniform perfusion at different depths of the heart muscle. We are using a combination of micro-CT imaging and vascular tree tracking techniques to study the fluid dynamic basis of blood supply to the heart muscle.*Blood supply to the uterus combines some of the most complex elements of vascular architecture and vascular control mechanisms in the cardiovascular system. A unique feature of this system is a group of spiral arteries which in the course of normal pregnancy undergo an intricate transformation in their geometry and mechanical properties. To date, the fluid dynamic principles governing the functional design of this system, particularly under pulsatile flow conditions, are not fully understood. A major study of the vascular architecture and control mechanisms involved is part of this proposal.******