 Arterial pressure wave

A small pressure disturbance in an elastic artery propagates through the coupled inertia of blood and compliance of the wall. If $\mathcal{A}$ is the undisturbed area, $\rho$ the mass density and $c$ the wave speed, the linearized equations give $c^2=\mathcal{A}/\rho dp/d\mathcal{A}$. A travelling pressure amplitude $p_{+}$ carries flow amplitude $\mathcal{A}{p}_{+}/(\rho c)$; the oppositely travelling wave has the opposite flow sign.