Relationship between blood pressure flow and resistance
The flow of blood through the vessel is determined by the difference in blood pressure between the two ends of the vessel, and the resistance against blood flow through the vessel, also known as the vascular resistance.
The function of the circulatory system is to supply blood needed for tissues - transport nutrients to organ tissues, and transport substances and hormones from some organs in the body to other places. The concentration of substances in the homeostasis in the body helps cells survive and perform their functions well.
Blood flow through a vessel is determined by two factors: (1) the difference in blood pressure between the two ends of the vessel, also known as the "blood pressure gradient", which pushes blood through the vessel. And (2) resistance against blood flow through the vessel, also known as vascular resistance. The figure explains this relationship, any blood vessel in the circulatory system.
Figure. Relationship between pressure, resistance, and blood flow. P1, pressure at the base of the vessel; P2, pressure at the other end of the vessel.
P1 re-introduces blood pressure at the base of the vasculature, and blood pressure at the other end as P2. The resistance occurs because of the collision between the bloodstream and the vascular endothelium along the vessel segment. Flow can be calculated by the following formula, also known as Ohm's law:
F = ∆P/R
where F is blood flow
∆P is the difference in blood pressure (P1-P2) between the two endpoints of the vessel.
R is the resistance.
Through this formula, the blood flow is proportional to the blood pressure difference but inversely proportional to the resistance.
Note that the difference in blood pressure between the two endpoints of the lumen, not the absolute intravascular pressure, determines the blood velocity. For example, if the blood pressure at both endpoints is 100 mmHg, there is no difference in blood pressure at these two endpoints so there is no blood flow even though the blood pressure is 100 mmHg.
Ohm's law, mentioned above, makes a few important points out of all the correlations that help the reader understand hemodynamic in the circulatory system. This formula is very important, so readers should also know some of its other algebraic formulas:
∆P = F x R