A 60 - year - old patient, known case of hypeension for the past 25 years underwent renal aery Doppler which showed narrowing and turbulence in right renal aery. If radius of aery is reduced by one - third, resistance increases by_____.

Flow a (U)4 ; U - radius 2 times 16 times 3 times 81 times 4 times 256 times This fouh power law makes it possible for aerioles responding with only small changes in diameter to nervous signal or local tissue chemical signals, either to turn off almost completely the blood flow to the tissue or at the other extreme to cause a vast increase in flow.