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Vascular resistance is the resistance that must be overcome for blood to flow through the circulatory system.The resistance offered by the systemic circulation is known as the systemic vascular resistance or may sometimes be called by another term total peripheral resistance, while the resistance caused by the pulmonary circulation is known as the pulmonary vascular resistance.
Metabolic vessels – capillaries; Capacitance vessels – veins; Particular feature of resistance vessels is ability to change lumen crossectional area and influence blood pressure. Human arteries or arterioles that are around 0.2 mm or smaller contribute to creation of the blood flow resistance and are called resistance arteries. [2] [3]
Blood resistance varies depending on blood viscosity and its plugged flow (or sheath flow since they are complementary across the vessel section) size as well, and on the size of the vessels. Assuming steady, laminar flow in the vessel, the blood vessels behavior is similar to that of a pipe.
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.
Vascular resistance occurs when the vessels away from the heart oppose the flow of blood. Resistance is an accumulation of three different factors: blood viscosity, blood vessel length and vessel radius. [30] Blood viscosity is the thickness of the blood and its resistance to flow as a result of the different components of the blood.
The narrowing of blood vessels leads to an increase in peripheral resistance, thereby elevating blood pressure. While vasoconstriction is a normal and essential regulatory mechanism for maintaining blood pressure and redistributing blood flow during various physiological processes, its dysregulation can contribute to pathological conditions.
An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. [ 1 ] Arterioles have muscular walls (usually only one to two layers of smooth muscle cells ) and are the primary site of vascular resistance .
The arterial resistivity index (also called as Resistance index, abbreviated as RI), developed by Léandre Pourcelot , is a measure of pulsatile blood flow that reflects the resistance to blood flow caused by microvascular bed distal to the site of measurement.
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