title: Progressive decrease of heart period variability entropy-based complexity during graded head-up tilt.
abstract: Complexity (or its opposite, regularity) of heart period variability has been related to age and disease but never linked to a progressive shift of the sympathovagal balance. We compare several well established estimates of complexity of heart period variability based on entropy rates [i.e., approximate entropy (ApEn), sample entropy (SampEn), and correct conditional entropy (CCE)] during an experimental protocol known to produce a gradual shift of the sympathovagal balance toward sympathetic activation and vagal withdrawal (i.e., the graded head-up tilt test). Complexity analysis was carried out in 17 healthy subjects over short heart period variability series ( approximately 250 cardiac beats) derived from ECG recordings during head-up tilt with table inclination randomly chosen inside the set {0, 15, 30, 45, 60, 75, 90}. We found that 1) ApEn does not change significantly during the protocol; 2) all indices measuring complexity based on entropy rates, including ad hoc corrections of the bias arising from their evaluation over short data sequences (i.e., corrected ApEn, SampEn, CCE), evidence a progressive decrease of complexity as a function of the tilt table inclination, thus indicating that complexity is under control of the autonomic nervous system; 3) corrected ApEn, SampEn, and CCE provide global indices that can be helpful to monitor sympathovagal balance.
authors.affiliation: Universita' degli Studi di Milano, Dipartimento di Tecnologie per la Salute, Istituto Ortopedico Galeazzi, Laboratorio di Modellistica di Sistemi Complessi, Via R. Galeazzi 4, 20161 Milan, Italy. alberto.porta@unimi.it
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Tomaso
authors.initials: T
authors.lastname: Gnecchi-Ruscone
authors.forename: Eleonora
authors.initials: E
authors.lastname: Tobaldini
authors.forename: Stefano
authors.initials: S
authors.lastname: Guzzetti
authors.forename: Raffaello
authors.initials: R
authors.lastname: Furlan
authors.forename: Nicola
authors.initials: N
authors.lastname: Montano
mesh_terms: D000328:Adult; D004562:Electrocardiography; D019277:Entropy; D005260:Female; D006321:Heart / Q000294:innervation / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D013564:Sympathetic Nervous System / Q000502:physiology; D018667:Tilt-Table Test / Q000379:methods*; D014630:Vagus Nerve / Q000502:physiology