Behavioral-independent features of complex heartbeat dynamics

To test the possibility that the multifractality in healthy heartbeat dynamics is related to neuroautonomic control, an attempt was made to analyze data from six subjects (four male, two female) who were administered a beta-blocking drug which reduces sympathetic control. Eight data sets from the six subjects for the second and/or third day of beta-blocker administration were analyzed. As a control, eight data sets for the same subjects but for the second and/or third day of placebo administration were also analyzed. The results indicate that when fluctuations in physical activity and other behavioral modifiers are minimized, a remarkable level of complexity of heartbeat dynamics remains, while for neuroautonomic blockade the multifractal complexity decreases.