Input for baroreflex analysis: which blood pressure signal should be used?

The baroreflex (BR) is an important physiological regulatory mechanism which reacts to blood pressure perturbations with reflex changes of target variables such as the heart period (electrocardiogram derived RR interval) or the peripheral vascular resistance (PVR). Evaluation of cardiac chronotropic (RR as a target variable) and vascular resistance (target PVR) BR arms was in previous studies mainly based on the use of the spontaneous variability of the systolic or diastolic blood pressure (SBP, DBP), respectively, as the input signals. The use of other blood pressure measures such as the mean blood pressure (MBP) as an input signal for BR analysis is still under investigation. Making the assumption that the strength of coupling along the BR indicates the more appropriate input signal for baroreflex analysis, we employ partial spectral decomposition to assess in the frequency domain the causal coupling from SBP, MBP or DBP to RR or PVR. Noninvasive beat-to-beat recording of RR, SBP, MBP and DBP and PVR was performed in 39 and 36 volunteers in whom orthostatic and cognitive loads were evoked respectively through head-up tilt and mental arithmetic task. At rest, the MBP was most tightly coupled with RR, in contrast to the analysis of the vascular resistance BR arm where the results showed similar importance of all blood pressure input signals. During orthostasis, the increased importance of SBP as the input signal for BR analysis along the cardiac chronotropic arm was demonstrated. In addition, the gain from MBP to RR was more sensitive to physiological state changes compared to gains with SBP or DBP signal as inputs. We conclude that the coupling strength depends not only on the analysed baroreflex arm but also on the selection of the input blood pressure signal and the physiological state. The MBP signal should be more frequently used for the cardiac baroreflex analysis

Information Domain Analysis of Respiratory Sinus Arrhythmia Mechanisms

Ventilation related heart rate oscillations - respiratory sinus arrhythmia (RSA) - originate in human from several mechanisms. Two most important of them - the central mechanism (direct communication between respiratory and cardiomotor centers), and the peripheral mechanism (ventilation-associated blood pressure changes transferred to heart rate via baroreflex) have been described in previous studies. The major aim of this study was to compare the importance of these mechanisms in the generation of RSA non-invasively during various states by quantifying the strength of the directed interactions between heart rate, systolic blood pressure and respiratory volume signals. Seventy-eight healthy volunteers (32 male, age range: 16.02-25.77 years, median age: 18.57 years) participated in this study. The strength of mutual interconnections among the spontaneous beat-to-beat oscillations of systolic blood pressure (SBP), R-R interval (RR signal) and respiration (volume changes - RESP signal) was quantified during supine rest, orthostatic challenge (head-up tilt, HUT) and cognitive load (mental arithmetics, MA) using bivariate and trivariate measures of cardio-respiratory information transfer to separate baroreflex and nonbaroreflex (central) mechanisms. Our results indicate that both basic mechanisms take part in RSA generation in the intact cardiorespiratory control of human subjects. During orthostatic and mental challenges baroreflex based peripheral mechanism becomes more important

The effect of orthostatic stress on multiscale entropy of heart rate and blood pressure

Cardiovascular control acts over multiple time scales, which introduces a significant amount of complexity to heart rate and blood pressure time series. Multiscale entropy (MSE) analysis has been developed to quantify the complexity of a time series over multiple time scales. In previous studies, MSE analyses identified impaired cardiovascular control and increased cardiovascular risk in various pathological conditions. Despite the increasing acceptance of the MSE technique in clinical research, information underpinning the involvement of the autonomic nervous system in the MSE of heart rate and blood pressure is lacking. The objective of this study is to investigate the effect of orthostatic challenge on the MSE of heart rate and blood pressure variability (HRV, BPV) and the correlation between MSE (complexity measures) and traditional linear (time and frequency domain) measures. MSE analysis of HRV and BPV was performed in 28 healthy young subjects on 1000 consecutive heart beats in the supine and standing positions. Sample entropy values were assessed on scales of 1–10. We found that MSE of heart rate and blood pressure signals is sensitive to changes in autonomic balance caused by postural change from the supine to the standing position. The effect of orthostatic challenge on heart rate and blood pressure complexity depended on the time scale under investigation. Entropy values did not correlate with the mean values of heart rate and blood pressure and showed only weak correlations with linear HRV and BPV measures. In conclusion, the MSE analysis of heart rate and blood pressure provides a sensitive tool to detect changes in autonomic balance as induced by postural change.Zuzana Turianikova, Kamil Javorka, Mathias Baumert, Andrea Calkovska, and Michal Javork

Changes in Heart Rate Variability and Complexity in Young Patients with Type 1 Diabetes Mellitus after A 17 Month Follow-Up

The objective of this study was to investigate short-term changes in cardiovascular autonomic dysregulation in young patients with Type 1 diabetes mellitus (DM)

The effect of orthostasis on recurrence quantification analysis of heart rate and blood pressure dynamics

The purpose of this paper is to investigate the effect of orthostatic challenge on recurrence plot based complexity measures of heart rate and blood pressure variability (HRV and BPV). HRV and BPV complexities were assessed in 28 healthy subjects over 15 min in the supine and standing positions. The complexity of HRV and BPV was assessed based on recurrence quantification analysis. HRV complexity was reduced along with the HRV magnitude after changing from the supine to the standing position. In contrast, the BPV magnitude increased and BPV complexity decreased upon standing. Recurrence quantification analysis (RQA) of HRV and BPV is sensitive to orthostatic challenge and might therefore be suited to assess changes in autonomic neural outflow to the cardiovascular system.M Javorka, Z Turianikova, I Tonhajzerova, K Javorka and M Baumer

Information transfer and information modification to identify the structure of cardiovascular and cardiorespiratory networks

none6siTo fully elucidate the complex physiological mechanisms underlying the short-term autonomic regulation of heart period (H), systolic and diastolic arterial pressure (S, D) and respiratory (R) variability, the joint dynamics of these variables need to be explored using multivariate time series analysis. This study proposes the utilization of information-theoretic measures to measure causal interactions between nodes of the cardiovascular/cardiorespiratory network and to assess the nature (synergistic or redundant) of these directed interactions. Indexes of information transfer and information modification are extracted from the H, S, D and R series measured from healthy subjects in a resting state and during postural stress. Computations are performed in the framework of multivariate linear regression, using bootstrap techniques to assess on a single-subject basis the statistical significance of each measure and of its transitions across conditions. We find patterns of information transfer and modification which are related to specific cardiovascular and cardiorespiratory mechanisms in resting conditions and to their modification induced by the orthostatic stress.Faes, L; Nollo, G; Krohova, J; Czippelova, B; Turianikova, Z; Javorka, MFaes, Luca; Nollo, Giandomenico; Krohova, J; Czippelova, B; Turianikova, Z; Javorka, M

Baroreflex analysis in diabetes mellitus: linear and nonlinear approaches

The aim of our study was to employ novel nonlinear synchronization approaches as a tool to detect baroreflex impairment in young patients with subclinical autonomic dysfunction in Type 1 diabetes mellitus (DM) and compare them to standard linear baroreflex sensitivity (BRS) methods. We recorded beat-to-beat pulse interval (PI) and systolic blood pressure (SBP) in 14 DM patients and 14 matched healthy controls. We computed the information domain synchronization index (IDSI), cross-multiscale entropy, joint symbolic dynamics, information-based similarity index (IBSI) in addition to time domain and spectral measures of BRS. This multi parametric analysis showed that baroreflex gain is well-preserved, but the time delay within the baroreflex loop is significantly increased in patients with DM. Further, the level of similarity between blood pressure and heart rate fluctuations was significantly reduced in DM. In conclusion, baroreflex function in young DM patients is changed. The quantification of nonlinear similarity and baroreflex delay in addition to baroreflex gain may provide an improved diagnostic tool for detection of subclinical autonomic dysfunction in DM.Michal Javorka, Zuzana Lazarova, Ingrid Tonhajzerova, Zuzana Turianikova, Natasa Honzikova, Bohumil Fiser, Kamil Javorka and Mathias Baumer

Redundancy and synergy in interactions among basic cardiovascular oscillations

The cardiovascular control system comprises a complex network of various control mechanisms operating on many time scales resulting in complex and mutually interconnected output signals (e.g. heart rate, systolic and diastolic blood pressures). The analysis of these interconnections could noninvasively provide an information on the regulatory mechanisms involved in cardiovascular control and thus could be potentially applied to better characterize cardiovascular dysregulation in pathological conditions. Our study demonstrates that the strength of interactions among signals changes with the time scale and as a response to changed autonomic state (orthostasis compared to supine rest). Novel insight regarding the interaction between two signals (sources) when influencing a target (third) signal could be obtained by the information-theoretic analysis of sources' redundancy and synergy

Cardiovascular and respiratory variability during orthostatic and mental stress: a comparison of entropy estimators

none8siThe aim of this study is to characterize cardiovascular and respiratory signals during orthostatic and mental stress as reflected in indices of entropy and complexity, providing a comparison between the performance of different estimators. To this end, the heart rate variability, systolic blood pressure, diastolic blood pressure and respiration time series were extracted from the recordings of 61 healthy volunteers undergoing a protocol consisting of supine rest, head-up tilt test and mental arithmetic task. The analysis was performed in the information domain using measures of entropy and conditional entropy, estimated through model-based (linear) and model-free (binning, nearest neighbor) approaches. Our results show that different types of stress elicited different responses in the employed indices. On one hand, entropy mainly reflected known changes in the variance of physiological time series. On the other hand, the information conveyed by conditional entropy allowed to characterize the complexity of the four time series during the two stress tasks: we found that cardiac and vascular dynamics underwent a reduction in complexity as a consequence of postural stress, while vascular and respiratory complexity increased as a result of mental stress. As for the performance of different estimators, we did not find substantial differences between model-based and model-free approaches, possibly indicating that significant non-linear dynamics did not appear in the studied conditions.Valente, M; Javorka, M; Turianikova, Z; Czippelova, B; Krohova, J; Nollo, G Faes, LValente, M; Javorka, M; Turianikova, Z; Czippelova, B; Krohova, J; Nollo, Giandomenico; Faes, Luc

Repolarization variability independent of heart rate during sympathetic activation elicited by head-up tilt

The fraction of repolarization variability independent of RR interval variability is of clinical interest. It has been linked to direct autonomic nervous system (ANS) regulation of the ventricles in healthy subjects and seems to reflect the instability of the ventricular repolarization process in heart disease. In this study, we sought to identify repolarization measures that best reflect the sympathetic influences on the ventricles independent of the RR interval. ECG was recorded in 46 young subjects during supine and then following 45 degrees head-up tilt. RR intervals and five repolarization features (QTend, QTpeak, RTend, RTpeak, and TpTe) were extracted from the ECG recordings. Repolarization variability was separated into RR-dependent and RR-independent variability using parametric spectral analysis. Results show that LF power of TpTe is independent of RR in both supine and tilt, while the LF power of QTend and RTend independent of RR and respiration increases following tilt. We conclude that TpTe is independent of RR and is highly affected by respiration. QTend and RTend LF power might reflect the sympathetic influences on the ventricles elicited by tilt. Graphical abstract.Fatima El-Hamad, Michal Javorka, Barbora Czippelova, Jana Krohova, Zuzana Turianikova, Alberto Porta, Mathias Baumer