Poiseuille's law states that the blood flow rate F ( in L/min ) through a major artery is directly proportional to the product of the fourth power of the radius r and the blood pressure P. During heavy exercise, normal blood flow rates sometimes triple. If the radius of a major artery increases by 5%, approximately how much harder must the heart pump?
A)about 2.47 times as hard
B)about 3.61 times as hard
C)about 1.22 times as hard
D)about 2.10 times as hard
E)about 2.22 times as hard

Question

Quizplus · Accepted Answer

If the radius increases by 5%, the new radius is 1.05r. The flow rate is proportional to r^4, so the new flow rate is (1.05)^4 times the original. (1.05)^4 ≈ 1.2155. To triple the flow rate, the heart must pump approximately 3/1.2155 ≈ 2.47 times as hard.

Poiseuille's Law States That the Blood Flow Rate F