### Total Fluid Energy:

The earlier equation showing how pressure and velocity yield total fluid energy, can be expanded to include gravitational potential energy. Rho x G x h is an expression of the gravitational positional energy. It is of lesser significance in our discussion here because the vascular system is a closed system. Expressions of total fluid energy can be further expanded to include thermal energy.

What if velocity is zero such that there is no kinetic energy? In an open container of fluid the pressure energy is zero at the surface, whereas the gravitational positional energy is maximal because the fluid could fall from the surface to the bottom. In contrast, at the bottom of the container the gravitational positional energy is zero whereas the pressure energy is maximal. As one is increasing, the other is decreasing, so that the total fluid energy is constant throughout the column of fluid. If this were not so, the fluid would continually move from top to bottom, bottom to top, which we know does not happen.