Parallel Resistance Calculations
or solving for Rx,
To illustrate this relationship empirically, assume that R1 = 5, R2 = 10 and R3 = 20.
In this example, Rx = 2.86.
This demonstrates two important principles regarding the parallel arrangement of blood vessels:
- The total resistance of a network of parallel vessels is less than the resistance of the vessel having the lowest resistance. Therefore, a parallel arrangement of vessels greatly reduces resistance to blood flow. That is why capillaries, which have the highest resistance of individual vessels because of their small diameter, constitute only a small portion of the total vascular resistance of an organ or microvascular network.
- When there are many parallel vessels, changing the resistance of a small number of these vessels will have little effect on total resistance for the segment.