<prompt> In laminar flow, if diameter is reduced to half ?Blood flow increases four foldBlood flow decreases four foldBlood flow increases sixteen-foldBlood flow decreases sixteen-fold  <response>: Ans. is d i.e., Blood flow decreases sixteen-foldIf everything else remains constant, blood flow is direactly poropoional to 4th power of radius.Thus, if the diameter or radius is reduced to half, blood flow will decrease sixteen-fold. 