One important area gradient force has been omitted in the Moens and Korteweg's Equation.

Pulse wave velocity is mostly related to the young's modulus by the Moens and Korteweg's formula. In deriving this formula, the wall's effect on the blood was ignored at the first step and the pressure gradient was considered as the only driving force in the axial flow of the blood. The local area gradient was assumed to be zero. However, for a real arterial system with compliance, the area gradient is automatically accompanied with the pressure gradient and it will contribute an area gradient force. This force has been omitted so far without any justification because it will contribute a nonlinear term and also leads an obstacle for the analogy with the transmission line theory. We give a quantitative evaluation of the ratio of the area gradient force to the pressure gradient force and find that it is more than 50% in the main artery. This shows the inadequacy and the inaccuracy of the pulse wave velocity derived based on this axial flow equation. We propose that starting from the radial equation of motion might provide an alternate, feasible method to study hemodynamics by energy concern.