This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Circulation: Biophysics of Pressure, Flow, and Resistance, Subject name: Physiology
If diameter of a vessel is increased double - 
Select and explain. 
A. Blood flow increases four fold, B. Blood flow decreases four fold, C. Blood flow increases sixteen-fold, D. Blood flow decreases sixteen-fold
C: Blood flow increases sixteen-fold
Answer: C: Blood flow increases sixteen-fold 
Explanation: Ans. is 'c' i.e., Blood flow increases sixteen-fold Poiseuille's Law (Hagen-Poiseille's law) o The Poiseuille's equation states that: -Where Q is the rate of flow. (Pl - P2) is the pressure difference across the vessel (provided P1 > P2), n is the viscocity of blood, r is the radius and L the length of the tubeo If everything else remains constant, blood flow is directly poroportional to 4th power of radiuso Thus, if the diameter (or radius) is increased to to double, blood flow will increase 16 times.