Radar-based respiration measurement is susceptible to upper body movement in addition to the respiratory motion of the chest. This parasitic movement can only be canceled using a dual radar system from the front and back. However, the larger hardware effort could be avoided if a physiological parameter is measured that is influenced by respiration only but not by the movement. This could then be used to indirectly derive breathing. In this paper a method is presented, how the respiration can be deduced despite of upper body movements. To achieve this, a Six-Port interferometer is used to measure the heart sound envelogram of a test person from which subsequently the respiration can be reconstructed.