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For this reason, the blood flow velocity is the fastest in the middle of the vessel and slowest at the vessel wall. In most cases, the mean velocity is used. [18] There are many ways to measure blood flow velocity, like videocapillary microscoping with frame-to-frame analysis, or laser Doppler anemometry. [19]
In the cardiovascular system, the pulsation frequency, density, and dynamic viscosity are constant, however the Characteristic length, which in the case of blood flow is the vessel diameter, changes by three orders of magnitudes (OoM) between the aorta and fine capillaries. The Womersley number thus changes due to the variations in vessel size ...
The flow profiles was first derived by John R. Womersley (1907–1958) in his work with blood flow in arteries. [1] The cardiovascular system of chordate animals is a very good example where pulsatile flow is found, but pulsatile flow is also observed in engines and hydraulic systems, as a result of rotating mechanisms pumping the fluid.
The up and down fluctuation of the arterial blood pressure is due to the pulsatile nature of the cardiac output and determined by the interaction of the stroke volume versus the volume and elasticity of the major arteries. The decreased velocity of flow in the capillaries increases the blood pressure, due to Bernoulli's principle.
Blood viscosity is a measure of the resistance of blood to flow. It can also be described as the thickness and stickiness of blood. This biophysical property makes it a critical determinant of friction against the vessel walls, the rate of venous return, the work required for the heart to pump blood, and how much oxygen is transported to tissues and organs.
The classic definition by MP Spencer and AB Denison of compliance is the change in arterial blood volume due to a given change in arterial blood pressure ().They wrote this in the "Handbook of Physiology" in 1963 in work entitled "Pulsatile Flow in the Vascular System".
Approximately, seven percent of the body's blood is in the capillaries which continuously exchange substances with the liquid outside these blood vessels, called interstitial fluid. This dynamic displacement of materials between the interstitial fluid and the blood is named capillary exchange. [5]
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.