Mechanical Aspects of Pulsatile Blood Flow

血液被广泛认为是生命的本质，但事实上，生命的本质不是血液，而是血液流动。当心脏停止跳动时，身体死亡不是因为缺乏血液，而是因为缺乏血液流动。这项建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，由无数的管子和管子接头组成。这一建议的基础是，对这个复杂系统的充分理解存在于力学领域，而不是医学领域。*血流有两个方面明确地属于力学领域：(1)血流的脉动性质赋予了系统一个动态维度，超越了通常的血液流动的“管道”观点，在这种观点中，血液流动的中断仅限于血管闭塞。这是对脉动血流的一种不完整的看法，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液流动也受到神经血管控制，这些神经血管控制起源于身体不同区域的血液供应需求，并由大脑中的控制中心调节。这些系统共同工作的方式还没有完全被理解，同样，这个主题完全属于力学领域。*这个提议的重点是研究三个特定器官中血液流动的这些动力学方面：大脑、心脏和子宫。每一个都有独特的机械问题，如下所述。*在大脑中，脉动的血液流动发生在坚硬的头骨的范围内。因此，压力和流量之间的关系不同于心血管系统的其他部分，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非侵入性研究，目的是更好地了解大脑血液流动的机制。*在心脏中，心脏肌肉的灌流对正常的心脏功能至关重要。目前尚不清楚心肌的血管系统如何在心肌的不同深度实现所需的持续和合理的均匀灌流。我们正在结合使用Micro-CT成像和血管树跟踪技术来研究向心肌供血的流体动力学基础。*向子宫供血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。这一系统的一个独特特征是一组螺旋动脉，在正常妊娠过程中，它们在几何和机械性能上经历了复杂的变化。到目前为止，指导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，还没有完全被理解。对所涉及的血管结构和控制机制的一项重要研究是这项建议的一部分。

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.******