Day-to-night variations of RR intervals complexity observed in 24-h ECG Holter R

Complexity of RR intervals can be measured by Sample entropy (SampEn) traditionally estimated only for a limited number of points by fixing the values of the embedding dimension "m" and distance threshold "r". Recently we have proposed a new and fast Norm Component Matrix (NCM) algorithm for SampEn calculation — it allows analyzing whole ranges of (m, r) values leading to entropy surfaces. This study is aimed at the analysis of these surfaces in the scope of day-to-night variations of RR intervals complexity estimated by the NCM.