Irreversibility in the interbeat interval time series and efficiency of the cardiac cycle

The variability of the cardiac cycle implies that in the long term it is irreversible. In this work we calculate the cycle's efficiency and quantify the irreversibility of interbeat interval time series. The results show that there is a variability of cardiac efficiency along the day for both healthy persons and congestive heart failure (CHF) patients, and there is a substantial reduction in efficiency for CHF patients. Analysis performed with the multiscale time irreversibility method applied to the interbeat interval time series, shows that the interbeat interval time series of healthy persons are irreversible and time series of CHF patients tend to reversibility.