17 Relative change in blood flow Another law of Poiseuille says that when blood flows along a blood vessel the flux F the volume of blood per unit time that flows past a given point is proportional to the fourth power of the radius R of the blood vessel KR We will show why this is true in Section 6 3 A partially clogged artery can be expanded by an operation called angioplasty in which a balloon tipped catheter is inflated inside the artery in order to widen it and restore the normal blood flow Show that the relative change in F is about four times the relative change in R How will a 5 increase in the radius affect the flow of blood