Fractal Dynamics in the RR Interval of Craniopharyngioma and Adrenal Tumor in Adolescence.

Abstract

Heart rate variability (HRV) is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the beat-to-beat interval and/or RR variability (where R is a point corresponding to the peak of the QRS complex of the ECG wave and RR is the interval between successive Rs) and other components extracted from these. HRV is a field of research interest in pathophysiology (in general) and cancer prognosis (more specifically). Adolescents with adrenal tumor or craniopharyngioma were investigated, herein. Αutonomic nervous system recordings were performed with Task Force® Monitor (gold standard of the Task Force of the European Society of Cardiology and the North American Society of Electrophysiology). The RR interval (RRI) time series calculations were performed with the MatLab® computational environment and included the estimation of fractal dimension and Lyapunov exponent. Fractal dimensions were calculated by estimating N and R, where N represents the number of "squares" needed for a fractal shape to be completed and their respective "square size" R. By definition, if the first derivative of d ln N/d ln R remains constant for a space of R, this is the fractal dimension of the shape, in the present case of the time series trajectory. We found that RRI manifested different fractal dynamics, thus, a complex pattern of progression in these two morbid entities, suggesting the need for further investigation in ANS contribution to tumor pathophysiology.