  We investigate an effective relativistic equation of state at finite values
of temperature and baryon chemical potential with the inclusion of the full
octet of baryons, the Delta-isobars and the lightest pseudoscalar and vector
meson degrees of freedom. These last particles have been introduced within a
phenomenological approach by taking into account of an effective chemical
potential and mass depending on the self-consistent interaction between
baryons. In this framework, we study of the hadron yield ratios measured in
central heavy ion collisions over a broad energy range and present the beam
energy dependence of underlying dynamic quantities like the net baryon density
and the energy density.
