Blood is flowing through a circuit with an inflow pressure of 100 mm Hg and an outflow pressure of 10 mm Hg. Each of the parallel circuits (R1, R2, R3, R4 and R5) has a resistance of 5 mm Hg/mL/min. What is the blood flow across this circuit?
Correct Answer: 90 ml/min
Description: In electrical theory, Ohm&;s law states that the resistance, R, equals the ratio of voltage drop, E, to current flow, I.R=E/ISimilarly, in fluid mechanics, the hydraulic resistance, R, may be defined as the ratio of pressure drop. Pi - Po, to flow, Q. P and P, are the pressures at the inflow and outflow ends, respectively, of the hydraulic system.R = P-PJOFor the resistance of vessels in parallel:1/R= l/R1 + 1/R2...... 1/R5Applying equation 3 to the given blood circuit, the resistance will be 1 mm Hg/mL/min. From Ohm&;s law (Equation 2), flow (Q) in a circuit would be,Q = P - Po/R By substituting corresponding values for inflow and outflow pressures, resistance of the given blood circuit in equation 4,Q= 100- 10/1 =90 mL/min(Refer: Ganong&;s Review of Medical physiology 23 edition, pg no: 602-604)
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