A simple method for evaluating the balance of the autonomic nervous system using photoplethysmography

A novel evaluation method for measuring the balance of the autonomic nervous system is proposed in this paper. The sympathetic and parasympathetic nervous systems operate on effector organs mostly antagonistically. Nevertheless there are some reports that a well-balanced state exists where both the sympathetic and parasympathetic nervous system are operating at a high level, and their working together well is necessary to maintain good health. Thus the balance of the autonomic nervous systems is evaluated in our study. The well-balanced state of the sympathetic and parasympathetic nervous systems cannot be described by the conventional autonomic nervous system evaluation method as it uses same parameter for both horizontal and vertical axes. From previous work, it is now possible to show the well-balanced state with a new 4-quadrant scatterplot which features axes with independent photoplethysmography-derived parameters. Here a new evaluation method derived from that work is suggested, using a simple 2-quadrant scatterplot for determining distressed or well-balanced states. The results of the verification experiments indicate that the proposed simple evaluation method has significance.