The bio-heat transfer equation is a macroscopic model for describing the heat transfer in microvascular tissue. So far the derivation of the Helmholtz term arising in the bio-heat transfer equation is not completely satisfactory. Our results show that this term may be understood as asymptotic result of boundary value problems which provide a microscopic description for microvascular tissue. In view of a future integration of the bio-heat transfer equation in a heterogeneous heat distribution model we present also asymptotic estimtates for first order correctors.