Hemodynamics and Cardiac Mechanics

The circulation of blood through the body’s network of vasculature and the mechanism by which it is propelled by the heart acting as a pump are discussed in physiological detail as well as through mathematical modeling. The circulatory system is composed of arteries, which conduct the pulsatile flow from heart contractions through smaller arterioles and very small capillaries. These capillaries merge to form venules, and finally veins, which return the blood to the heart after the exchange of oxygen and other nutrients has been accomplished. Blood vessels are composed of four layers of tissue: endothelial lining, elastin fibers, collagen fibers, and smooth muscle. The elastic properties of blood vessels can be modeled, and wall stresses can be evaluated, assuming they act as thin-walled pressure vessels. The stresses in the heart can also be modeled, assuming it acts as a thick-walled elastic cylinder under pressure. At the microcirculation level, the exchange of oxygen and other nutrients is accomplished through diffusion through the walls of the vessels. Finally, the organization of data, such as flow rates, pressures, and other variables that are relevant to modeling and analyzing circulatory phenomena, is facilitated through the use of dimensional analysis, which can create the dimensionless ratios that are most pertinent to elucidating the phenomena under examination.