##### Page 21, hemodynamics, Dr. D. Penney

__Resistance (continued..)__

The **concept of resistance comes out of the Poiseuille equation.** The Poiseuille equation can be rearranged to a form in which flow is equal to driving pressure times all of the other factors, {(pie / 8) x (r^{4} / length) x (1 / eta)}.
If these factors represent conductance, then resistance is equal to one over these factors, since resistance is the reciprocal of conductance. Rearranging the equation, flow becomes equal to the change in pressure divided by resistance, or, resistance is equal to P_{1}-P_{2} divided by flow. Thus, we have an expression for resistance.

Note that this equation is similar to Ohm's law for electrical circuits, where resistance is equal to voltage divided by current. [SEE MISCONCEPTION 19]

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