Figure 1

Multiscale time irreversibility (asymmetry) analysis of the cardiac interbeat interval sequences derived from 24 h Holter monitor recordings of representative subjects: (a) healthy young (Yng); (b) healthy elderly (Eld); (c) congestive heart failure (CHF); and (d) atrial fibrillation (AF). Scale factor is referenced to heartbeat number. For each scale, the values of $A_I$ from the dotted and solid lines reflect, respectively, the average amount of “energy” associated with increases and decreases of the heart rate (see text). (e) Asymmetry index $A_I$ for groups of 26 healthy young subjects ($A_I=8.68\pm 3.40$, $\mathrm{\text{mean}}\pm \mathrm{\text{standard deviation}}$), 46 healthy elderly subjects ($A_I=3.44\pm 2.67$), 43 CHF subjects ($A_I=0.13\pm 1.80$), and 9 subjects with AF ($A_I=-0.04\pm 1.01$). Differences between groups are significant ($p<0.005$, $t$ test), with the exception of the two pathologic states (CHF vs AF). Cardiac interbeat interval time series obtained during the sleeping period yield comparable results. Therefore, nonstationarities due to physical activity do not account for these asymmetry properties. Note that, in terms of the mean $A_I$ values, the results indicate that the time series from the group of healthy young subjects are the most temporally irreversible, followed by those from the group of healthy elderly subjects and those from the groups of patients, both of which have $A_I$ values close to zero.Reuse & Permissions