Entropy in Cardiac Autonomic Nervous System of Adolescents with General Learning Disabilities or Dyslexia.

Heart rate variability (HRV) represents one of the two key markers of the autonomic nervous system. It is measured by the time variation in the beat-to-beat interval, while the period between successive beats is defined as the RR interval (RRI). Its components are classified as linear and non-linear. In the field of psychophysiology, HRV is investigated as a key player of possible predictive or diagnostic value. Female adolescents with general learning disabilities or dyslexia were recruited at the Center for Adolescent Medicine and UNESCO Chair on Adolescent Health Care of the National and Kapodistrian University of Athens. Adolescents were further assessed for HRV. Data were collected with the Task Force® Monitor at the Cardiovascular Laboratory of the Biomedical Research Foundation of the Academy of Athens. The RRI time-series were estimated for approximate entropy (AE), conditional entropy (CE), corrected conditional entropy (CCE), fuzzy entropy (FE), permutation entropy (PE), sample entropy (SE), and Shannon's entropy (ShE). RRI manifested complex dynamics, indicating a complex pattern of progression. This finding suggests that RRI conceals non-linear dynamics, which if investigated in depth could provide more knowledge on the relation between RRI and learning disorders.