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 Gives the relationship between resistance to flow and vessel dimensions and is analogous to Ohm's Law.

 It applies to laminar flow of incompressible uniformly viscous fluids (described as “Newtonian Fluids”) in uniform vessels.

The law does not apply to pulsatile flow.

 Its main application is in peripheral vessels where flow is almost steady.

 The Poiseuille equation can be derived by inserting the factors which affect resistance (R) into Ohm's Law. (for laminar flow in a vessel of length l, radius r and blood viscosity η)So, with substitution,

 Significance of Poiseuille's Law:Because r in this equation is raised to the fourth power, slight changes in vessel diameter (radius) cause tremendous changes in flow.An increase in viscosity (e.g., with dehydration) will contribute to a decrease in blood flow.