  We analytically work out the cumulative, i.e. averaged over one orbital
revolution, time variations of the radial velocity v_r of a typical S star
orbiting the Supermassive Black Hole (SBH) hosted by the Galactic Center (GC)
in Sgr A* caused by several dynamical effects. They are the general
relativistic gravitoelectromagnetic (GEM) fields of the SBH, its quadrupole
mass moment Q2, and a diffuse dark matter distribution around the SBH. All of
them induce non-zero secular radial accelerations proportional to the
eccentricity e of the orbit. By taking the S2 star, orbiting the SBH along a
highly eccentric (e = 0.8831) ellipse with a period Pb = 15.9 yr, we
numerically compute the magnitudes of its radial accelerations (Abridged).
