Characterization of complex heart rate dynamics and their pharmacological disorders by non-linear prediction and special data transformations

Objective: The aim of the presented method was the characterization of different complex heart rate dynamics in conscious rabbits as well as during general anaesthesia and vagal blockade. This was done by non-linear prediction of original measured and special surrogate data in the phase space. Method: The development of the prediction error in dependence on the prediction time interval was investigated in the phase space. Two kinds of surrogate data were produced and tested with regard to non-linearities and orientation in the phase space, Typical characteristics of prediction error development were shown for simulated uncorrelated stochastic, correlated stochastic, regular deterministic, and deterministic chaotic signals. These characteristics were used to evaluate the measured heart rate data in connection with tests of surrogate data. Results: It could be shown that heart rate fluctuation cannot be described by one of these ideal models alone. Common consideration of all investigated prediction characteristics indicated chaos in the heart mts of conscious rabbits as well as during anaesthesia and vagal blockade, where non-linear correlated stochastic properties could not be excluded, The different amount of non-linearites and orientation was described quantitatively. Conclusions: Detailed analysis of prediction error development in the phase space, connected with tests for non-linearities and orientation, enabled a specific quantitative characterization of complex heart rate dynamics and their pharmacological disorders,