<prompt> If radius of a vessel is doubled then the blood flow is increased by?8 times16 times32 times256 times  <response>: Ans. B 16 timesRef: Ganong: 26th ed. P 563 The influence of lumen diameter on resistance is dramatic. This is because resistance is inversely proportional to the radius of the blood vessel one-half of the vessels diameter raised to the fourth power R1r4. This means, that if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times. And if an artery or arteriole dilates to twice its initial radius, then resistance in the vessel will decrease to 116 of its original value and flow will increase 16 times. 