Mechanical Aspects of Pulsatile Blood Flow

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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.******