Interrelationships of Pressure, Flow, and Resistance Blood flow through a blood vessel is determined by two factors:
(1) pressure difference of the blood between thetwo ends of the vessel, also sometimes called
―pressure gradient‖ along the vessel, which is the force that pushes the blood through the vessel, and
(2) the impediment to blood flow through the vessel, which is called vascular resistance. Figure 14-3
demonstrates these relationships, showing a blood vessel segment located anywhere in the circulatory
system. P1 represents the pressure at the origin of the vessel; at the other end, the pressure is P2.
Resistance occurs as a result of friction between the flowing blood and the intravascular endothelium
all along the inside of the vessel. The flow through the vessel can be calculated by the following
formula, which is called Ohm’s law : in which F is blood flow,
P is the pressure difference.
