This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
Poiseille's-Hagen law is related to 
Select and explain. 
A. Airflow resistance, B. Rate of blood flow, C. Measurement of BP, D. None of the above
B: Rate of blood flow
Answer: B: Rate of blood flow 
Explanation: In the small blood vessels, essentially all the blood is near the wall, so extremely rapidly flowing central stream of blood doesn&;t exist. By integrating the velocities of all the concentric rings of flowing blood and multiplying them by the areas of the rings one can derive the formula known as poiseuille&;s law.In the equation, the rate of blood flow is directly propoional to 4th power of the radius of vessel.Ref: Guyton and Hall, Textbook of medical physiology, 2nd South Asia Edition, page no. 233