Inertance relates the pressure drop with the acceleration of flow. When blood flow is subjected to an increase in pressure difference the flow will change. Assuming no friction, the relation between the pressure drop, ΔP(t) and the rate of change of blood flow dQ/dt, depends on the density of the blood, ρ, the cross-sectional area, A = πri2, and the length, l, of the blood vessel. We call this combined effect the inertance, L = ρ l/A. Inertance pertains to oscillatory pressure and flow and plays a dominating role in large blood vessels, where the viscous resistance is small and pulsatility is considerable. Inertance and Poiseuille resistance together form the basis of the Oscillatory Flow Theory. The inertance and vessel compliance in combination determine the wave speed and the characteristic impedance of a blood vessel.
KeywordsBlood density Flow reversal Aortic valves Wave speed Characteristic impedance
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