US Patent 8721559 Non-invasive method and device for measuring cardiac output

A system comprising a housing containing a signal generator coupled to an antenna and a dielectric material disposed about the antenna. The device is adapted to generate and direct a plurality of signals towards the heart of the person and measure a magnitude of a signal returned from the heart. The device further comprises a processor to compare differences between a magnitude of a signal propagated and the magnitude of the signal returned off the heart and determine a signal frequency having a maximum return loss value based on those differences. The processor also estimates a change in the amplitude of motion of a portion of a wall of the heart based on the differences between the magnitude of the signal propagated by the device and the magnitude of the signal returned off of the portion of the heart.