Poiseuille's Law

The biggest surprise in the application of Poiseuille's law to fluid flow is the dramatic effect of changing the radius.

A decrease in radius has an equally dramatic effect, as shown in blood flow examples.

Blood Flow Examples

Blood Flow Examples

Suppose you have an emergency requirement for a five-fold increase in blood volume flowrate (like being chased by a big dog)? How does your body supply it?

According to Poiseuille's law, a five-fold increase in blood pressure would be required if the increase were supplied by blood pressure alone!

But the body has a much more potent method for increasing volume flowrate in the vasodilation of the small vessels called arterioles.

Since the smaller vessels provide most of the resistance to flow, the arterioles in their position just prior to the capillaries can provide a major controlling influence on the volume flowrate. This system of small vessels can constrict flow to one part of the body while enhancing the flow to another to meet changing demands for oxygen and nutrients.

Blood Flow Examples