= Pressure-flow phase lag from one arterial reflection
{title2=$\omega\Delta t=\arg[1-r^2+2ir\sin\vartheta]$}
For incident and reflected harmonic <arterial pressure waves> with real $0<r<1$, the local <pressure> and flow phasors are proportional to $1+re^{-i\vartheta}$ and $1-re^{-i\vartheta}$. Their maximum-time difference is the displayed phase lag, on the branch $0<\vartheta<\pi$. Here $\vartheta=2\omega d/c$ is the round-trip phase to the reflector. Its derivative has the sign of $\cos\vartheta$. Raising the <wave speed> reduces the lag when $0<\vartheta<\pi/2$, but increases it when $\pi/2<\vartheta<\pi$. This conditional harmonic model does not establish an age trend for arbitrary vascular geometry or measurement stations beyond the sole reflector.
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