MEASURING REGULARITY BY MEANS OF A CORRECTED CONDITIONAL ENTROPY IN SYMPATHETIC OUTFLOW

A new method for measuring the regularity of a process over short data sequences is reported. This method is based on the definition of a ne w function (the corrected conditional entropy) and on the extraction o f its minimum. This value is taken as an index in the information doma in quantifying the regularity of the process. The corrected conditiona l entropy is designed to decrease in relation to the regularity of the process (like other estimates of the entropy rate), but it is able to increase when no robust statistic can be performed as a result of a l imited amount of available samples. As a consequence of the minimisati on procedure, the proposed index is obtained without an a-priori defin ition of the pattern length (i.e. of the embedding dimension of the re constructed phase space). The method is validated on simulations and a pplied to beat-to-beat sequences of the sympathetic discharge obtained from decerebrate artificially ventilated cats. At control, regular, b oth quasiperiodic and periodic (locked to ventilation) dynamics are ob served. During the sympathetic activation induced by inferior vena cav a occlusion, the presence of phase-locked patterns and the increase in regularity of the sympathetic discharge evidence an augmented couplin g between the sympathetic discharge and ventilation. The reduction of complexity of the neural control obtained by spinalization decreases t he regularity in the sympathetic outflow, thus pointing to a weaker co upling between the sympathetic discharge and ventilation.