According to this definition, the emphasis is on the fluid and solid mechanics of the system. In the present review, “hemodynamics” refers to “the physical study of flowing blood and of all the solid structures (such as arteries) through which it flows” ( 64). In medical contexts, the term “hemodynamics” often refers to basic measures of cardiovascular function, such as arterial pressure or cardiac output. The circulatory system consists of the heart and an extensive branched system of vessels containing blood, whose primary function is the transport of oxygen, nutrients and other substances and heat throughout the body. Consideration of hemodynamics is essential for a comprehensive understanding of the functioning of the circulatory system. Biological responses to these forces are important in the control of blood flow and the structural remodeling of vessels, and also play a role in major disease processes including hypertension and atherosclerosis. The forces acting on vessel walls include shear stress resulting from blood flow and circumferential stress resulting from blood pressure. In the microcirculation, the fact that blood is a suspension of cells strongly influences its flow properties and leads to a non-uniform distribution of hematocrit among microvessels. In large arteries, the propagation of the pressure pulse depends on the elastic properties of the artery walls.
Depending on the vessel diameter and other physical parameters, a wide variety of flow phenomena can occur. The relationship between driving pressure and flow in a given vessel can be understood by considering the viscous and inertial forces acting on the blood. The main factors involved are the pulsatile driving pressure generated by the heart, the flow characteristics of blood, and the geometric structure and mechanical properties of the vessels. A review is presented of the physical principles governing the distribution of blood flow and blood pressure in the vascular system.
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