[Methodology in the analysis of asymmetry in fluctuations of heart rate]

Time series of R-R intervals show fluctuations which are neither symmetric regarding the changes in length of heart beats nor regarding the number of heart beats during the phases of heart rate acceleration and deceleration. These features of heart rate variability cannot be quantified by the analysis of the beat-to-beat variability or by the spectrum analysis of heart rate. The analysis of asymmetry using the distribution function of the differences between consecutive R-R intervals creates measures for the total, central, and peripheral asymmetry. These measures quantify different aspects of the shape of the distribution function. The asymmetry measures are either based on the amount of difference between consecutive R-R intervals or the number of lengthening R-R intervals in a sequence of heart beats. The analysis of asymmetry of R-R interval time series shows differences among test subjects during rest.