The invention refers to an implantable pulse generator system (10) that comprises a nerve stimulation unit (80) for generating and delivery of vagal nerve stimulation pulses, at least one autonomic tone sensor (82) for determining an autonomic status of a user and generating an autonomic status representing signal and a control unit (62) that that is connected to the nerve stimulation unit (80) and the autonomic tone sensor (82). The control unit (62) is configured to control the nerve stimulation unit (80) to generate vagal nerve stimulation pulse trains that are adapted to cause vagal nerve stimulation (VNS) with varying intensity, depending on the autonomic status representing signal. The control unit (62) is further configured to evaluate the autonomic status representing signal in a moving window and to thus generate an evaluated autonomic status representing signal. Further, the control unit (62) is configured to gradually increase the intensity of VNS when the evaluated autonomic status representing signal indicates an autonomic tone that is shifting toward more sympathetic dominance, and gradually decrease the intensity of VNS when the autonomic status representing signal indicates an autonomic tone that is shifting toward more parasympathetic dominance, wherein the gradual increase and the gradual decrease of the intensity of the VNS follow two different curves.
