Mathematics and Biology

Parameter Values Historical Background

Math Awareness Month 1999

Poiseuille's Law: What It Involves

Consider the following schematic of a blood vessel:

As the diagram shows, and as the formula has stated, Poiseuille's law relates the flow rate with the pressure, viscosity, vessel radius and length. For the purposes of this exhibit, we will always assume that the vessel in consideration is a small artery or an arteriole.

Units of Measurement

Pressure
mmHg (millimeters of mercury) are used for measurement. For the formula, convert to Pa (Pascals) by multiplying the mmHg by 133.3.
Viscosity
P (Poise) are the units (often with standard metric prefixes like centi- or milli-). For the formula, convert to (Pa s) by dividing the value by 10.
Radius
mm (millimeters) or micrometers are appropriate dimensions, but it is most useful in the formula to use cm (centimeters).
Length
cm (centimeters) are most convenient for measurements and for the formula.

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D. Brian Walton is supported by a National Science Foundation Graduate Research Fellowship.