A method of treating a medical condition in a patient using an implantable medical device, comprising providing an electrical signal generator； providing at least a first electrode operatively coupled to the electrical signal generator and to a vagus nerve of the patient； sensing cardiac data of the patient； determining at least a first cardiac parameter based upon said cardiac data； setting at least a first value； declaring an unstable brain state of a patient from said at least a first cardiac parameter and said at least a first value； and adjusting the at least a first value. Also, a computer readable program storage device encoded with instructions that, when executed by a computer, performs the method. In addition, the implantable medical device used in the method.
