Nonlinear analysis of the separate contributions of autonomic nervous systems to heart rate variability using principal dynamic modes

This work introduces a modified principal dynamic modes (PDM) method, which for the first time is able to separate the dynamics of sympathetic and parasympathetic nervous activities. The minimum set of expansion basis functions, which is required to achieve a given mean-square approximation, is termed PDMs of the nonlinear system. We found that the first two dominant PDMs have similar frequency characteristics for parasympathetic and sympathetic activities. Validation of the purported separation of parasympathetic and sympathetic activities was performed by the application of the autonomic nervous system blocking drugs atropine and propranolol. These results are consistent for all nine of our healthy human subjects using our modified PDM approach in both of the conditions of single blockade and double blockade. Comparison of our method to the conventional low/high frequency ratio. shows that our proposed approach provides more accurate assessment of the autonomic nervous balance.