Conditional symbolic analysis detects nonlinear influences of respiration on cardiovascular control in humans

Abstract

We propose a symbolic analysis framework for the quantitative characterization of complex dynamical systems. It allows the description of the time course of a single variable, the assessment of joint interactions and an analysis triggered by a conditioning input. The framework was applied to spontaneous variability of heart period (HP), systolic arterial pressure (SAP) and integrated muscle sympathetic nerve activity (MSNA) with the aim of characterizing cardiovascular control and nonlinear influences of respiration at rest in supine position, during orthostatic challenge induced by 80° head-up tilt (TILT) and about 3 min before evoked pre-syncope signs (PRESY). The approach detected (i) the exaggerated sympathetic modulation and vagal withdrawal from HP variability and the increased presence of fast MSNA variability components during PRESY compared with TILT; (ii) the increase of the SAP–HP coordination occurring at slow temporal scales and a decrease of that occurring at faster time scales during PRESY compared with TILT; (iii) the reduction of the coordination between fast MSNA and SAP patterns during TILT and PRESY; (iv) the nonlinear influences of respiration leading to an increased likelihood to observe the abovementioned findings during expiration compared with inspiration one. The framework provided simple, quantitative indexes able to distinguish experimental conditions characterized by different states of the autonomic nervous system and to detect the early signs of a life threatening situation such as postural syncope.

Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis

“…The univariate SA described in Porta et al 10 was applied to symbolize the HP and SAP series and reduce the redundancy of patterns and the JSA set in Porta et al 15 was carried out to assess the degree of the HP-SAP coupling. Briefly, the HP and SAP series were transformed into a sequence of ξ=6 symbols.…”

“…The univariate SA has been extended to become joint SA (JSA) with the aim of assessing the interactions between two series such as HP and systolic arterial pressure (SAP) variabilities 13 - 17 , HP variability and respiration 17 - 19 , and HP and ventricular repolarization duration variabilities 20 , 21 . Higher levels of integration of neural reflexes can be studied when JSA is gated according to a periodical input such as the respiratory activity 15 .…”

Complex and Nonlinear Analysis of Heart Rate Variability in the Assessment of Fetal and Neonatal Wellbeing

“…In 2015, Porta et al [81] extended the short-term symbolic dynamics procedure [34] to a bivariate and multivariate ones-the joint symbolic analysis (JSA) and the joint conditional symbolic analysis (JCSA). In principle, they created for two time series (x, y) for each time series separately the pattern 0 V, 1 V, 2LV and 2UV.…”

Enhancing dynamical signatures of complex systems through symbolic computation

“…The contributions can be roughly divided into theoretically oriented studies, where the methodology is the focus and archetypal examples of applications are provided for illustrations, and problem-driven investigations, where the emphasis is on the application, whereas mathematical details are discussed without a systematic approach. It is worth stressing that the majority of contributions provide a comprehensive extension to the multivariate case [20][21][22][23][24][25][26][27], thus providing tools fully helpful in contexts where multiple traces are acquired.…”

“…Among the application-driven contributions, Cysarz et al [28] apply several symbolization strategies to spontaneous beat-to-beat changes of fetal heart period and test their performances in following the development of the fetus during gestation; Valencia et al [29] show that symbolic indexes derived from the beat-to-beat series of heart period and ventricular repolarization duration separate ischaemic-dilated cardiomyopathy patients and healthy age-matched controls better than more traditional linear time and frequency domain markers; Schlemmer et al [30] propose a method based on symbolization to study sleep stage transitions and their modifications in relation to ageing and sleep disorders; Daw et al [23] provide an industry-driven application of symbolic analysis to control dilute combustion instabilities in a multi-cylinder spark-ignited engine; Baumert et al [24] review applications exploiting joint symbolic analysis to identify the pathophysiological changes of specific cardiovascular control mechanisms such as cardiac baroreflex and cardiopulmonary reflexes; Schulz et al [25] present an application of a high-resolution joint symbolic analysis to separate patients suffering from paranoid schizophrenia from their healthy first-degree relatives and age-matched controls; Porta et al [26] propose a conditional joint symbolic technique to assess the nonlinear interferences of respiration over cardiac and sympathetic 'baroreflexes' and apply it to an experimental protocol designed to evoke postural syncope; and Lee et al [27] review the basic principles of the neurobiology of consciousness, the problem of 'covert consciousness' (i.e. the presence of conscious experience coupled with the absence of responsiveness) and the recent advances in assessing levels of consciousness and cortical connectivity using symbolic dynamics and symbolic transfer entropy.…”