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.

A Refined Multiscale Self-Entropy Approach for the Assessment of Cardiac Control Complexity: Application to Long QT Syndrome Type 1 Patients

“…It is well-known that the complexity of HP, as estimated by the RMSCE of HP, is under vagal control at short time scale [12,13,15,42,43] and under sympathetic control at long time scale [12,13,15]. This study confirms these observations.…”

“…This finding suggested that having a reduced complexity of the cardiac control both at the level of sinus node and ventricles during DAY (i.e., when the arrhythmic risk is greatest in LQT1) is a protective factor [13]. Since AMCs are characterized by a more reactive sympathetic control [45] and a less reactive vagal regulation [45][46][47], this reduced complexity of the sympathetic control might be the result of the synchronization of neural inputs operating at slightly different temporal scales performed by the higher sympathetic driver [43,48]. However, this study added a new, relevant, piece of information.…”

Clinical impact of evaluation of cardiovascular control by novel methods of heart rate dynamics

“…Approximate entropy did not change during graded head-up tilt in 17 healthy subjects, a finding which was explained to be due to the bias of considering self-matches. Instead, corrected approximate entropy, sample entropy and corrected conditional entropy showed a progressive decrease as a function of the tilt table inclination (Porta et al 2007a). This may indicate that a shift of the sympathovagal balance towards sympathetic activation and vagal withdrawal decreases the complexity of heart rate dynamics.…”

Heart rate variability and critical flicker fusion frequency changes during and after parachute jumping in experienced skydivers

“…The improved accuracy of SampEn statistics makes them useful in the study of experimental clinical cardiovascular and other biological time series (Richman and Moorman 2000). It has been established that complexity of beat-to-beat variability was controlled by the ANS (Porta et al 2007a): heartbeat complexity could be reduced by vagal blockade (Penttila et al 2003) when vagal activation increased complexity (Porta et al 2007b). Sympathetic excitation by pharmacological (Penttila et al 2003) or physiological method (Porta et al 2007a) reduced complexity and sympathetic blockade with propranolol increased irregularity of the HR (Lepoluoto et al 2005).…”

“…It has been established that complexity of beat-to-beat variability was controlled by the ANS (Porta et al 2007a): heartbeat complexity could be reduced by vagal blockade (Penttila et al 2003) when vagal activation increased complexity (Porta et al 2007b). Sympathetic excitation by pharmacological (Penttila et al 2003) or physiological method (Porta et al 2007a) reduced complexity and sympathetic blockade with propranolol increased irregularity of the HR (Lepoluoto et al 2005). FrD and SampEn of HR time series correlate highly with each other and also with the high-frequency power and hence appear to reflect vagal modulation of HR variability (Yeragani et al 1993).…”