# Resistance to Flow

Not Reviewed
"R" =
Tags:
Rating
ID
JustinLiller.Resistance to Flow
UUID
17f11a17-eda2-11e3-b7aa-bc764e2038f2

Because it is often difficult or impossible to measure the radii of all vessels in a vascular bed, we designate (8Ln)/(PIr^4), the inverse of the term in Poiseuille's law, as the resistance to flow, R, which is equal to the pressure difference (P_1 - P_2) across a vascular bed divided by the flow rate, Q:

R = (P_1 - P_2)/Q = (8Ln)/(pir^4)