The present invention reliably computes cardiac output with a noninvasive procedure. The system measures the electrical impedance of a patient's body, during a time interval of interest. The system then obtains frequency transforms of various time segments of the first derivative of the impedance signal....http://www.google.co.uk/patents/US5423326?utm_source=gb-gplus-sharePatent US5423326 - Apparatus and method for measuring cardiac output
