A device for use as a rate-responsive pacemaker is disclosed in which the pacing interval is controlled by the amount of energy contained in a raw signal generated by a suitable physiological sensor and processed by an energy converter to generate an output energy signal coupled to the pacemaker control...http://www.google.com/patents/US4940053?utm_source=gb-gplus-sharePatent US4940053 - Energy controlled rate-responsive pacemaker having automatically adjustable control parameters
