Małgorzata Andrzejewska
supervisor: Jan Żebrowski
Physiological systems, such as the human body, for example, are considered complex. They consume energy to build into more complex and ordered structures. This ability to self-organize is linked to the directionality of energy flow and the irreversibility of the processes involved. The irreversibility over time is greater in healthy and young organisms. The decrease of irreversibility in time can relate to aging of the organism or with diseases. Many studies indicate that such a decrease can be linked to reduced heart rate variability (HRV). In many important pathologies, such as sudden cardiac death, efficient clinical indices which could be used for risk stratification and better patient management are still missing. Visibility graphs (VG) allow mapping time series to the form of graphs. VGs can be used to study the information contained in nonlinear signals like RR or QT intervals. This approach can be extended to analyze multivariate time series using multiplex VG. I will focus on comparison whether beta blockers (BB), which are used as pharmacological treatment in LQTS treatment, have an impact on non-linear parameters of HRV. VG methods will be compared with the results for time asymmetry indices. I observe that patients taking BB are characterized by higher irreversibility when characteristic of univariate time series is considered. However, for multivariate time series, VG similarity is unchanged, which concludes that BB do not change physiological network.