Search results for "dynamic"
showing 10 items of 12329 documents
Comparison of Methods for the Assessment of Nonlinearity in Short-Term Heart Rate Variability under different Physiopathological States
2019
Despite the widespread diffusion of nonlinear methods for heart rate variability (HRV) analysis, the presence and the extent to which nonlinear dynamics contribute to short-term HRV are still controversial. This work aims at testing the hypothesis that different types of nonlinearity can be observed in HRV depending on the method adopted and on the physiopathological state. Two entropy-based measures of time series complexity (normalized complexity index, NCI) and regularity (information storage, IS), and a measure quantifying deviations from linear correlations in a time series (Gaussian linear contrast, GLC), are applied to short HRV recordings obtained in young (Y) and old (O) healthy su…
Occult HBV infection and suppression of HCV replication in the early phase of combination therapy for chronic hepatitis C
2003
Occult HBV infection in subjects with chronic hepatitis C is related to more severe disease outcome. It has been suggested that it might reduce sensitivity to antiviral treatment.To assess in HBsAg negative subjects with chronic hepatitis C any effect of the presence of HBV genomes in the liver on the early kinetics of HCV-RNA under PEG-IFN plus ribavirin.Twenty-two anti-HCV and HCV-RNA positive subjects, with biopsy-proven chronic hepatitis C (M/F 15/7; 50 +/- 8.6 years, 16 genotype 1b) were given PEG-IFN alpha 2b 1.0 microg qw plus ribavirin (800 to 1,200 mg daily according to body weight) for an intended 52 week period. Early virological response was assessed over the first 4 weeks of th…
The main trends in the palaeodemography of the 7th-18th century population of Latvia
2006
The study represents palaeodemographic research of osteological material of 3304 individuals from the funds of the Anthropological Laboratory of the Institute of History of the University of Latvia in Riga, dating from the 7 th to the 18 th century AD. Compensated life expectancy at birth is varying between 20.3 and 22.2 years during the research period. Crude mortality has changed between 49.3 and 45 %o. In the early period (7 th - 13 th century) there is a significant male prevalence (2.2 - 1.4); female life expectancy at the age of 20 is on average 6.6 years less than for males. This difference decreases to 5.4 years in the 13 th - 18 th century. According to historical demography, femal…
Subchronic Antidepressant Treatment with Venlafaxine or Imipramine and Effects on Blood Pressure and Heart Rate: Assessment by Automatic 24-Hour Moni…
1996
Venlafaxine is a new nontricyclic antidepressant inhibiting the reuptake of serotonin, noradrenaline, and, to a lesser extent, dopamine without antagonizing cholinergic, histaminergic, or noradrenergic receptors. Significantly, in a first placebo-controlled safety and efficacy study, high doses of venlafaxine increased blood pressure in some study subjects. In order to investigate further the effect of subchronic antidepressant drug treatment on blood pressure and heart rate, the effects of a conventional tricyclic (imipramine) and a structurally different phenethylamine antidepressant (venlafaxine) were compared. Sixteen inpatients with major depression (melancholic type) were treated for …
Instantaneous transfer entropy for the study of cardio-respiratory dynamics
2015
Measures of transfer entropy have been proposed to quantify the directional coupling and strength between two complex physiological variables. Particular attention has been given to nonlinear interactions within cardiovascular and respiratory dynamics as influenced by the autonomic nervous system. However, standard transfer entropy estimates have shown major limitations in dealing with issues concerning stochastic system modeling, limited observations in time, and the assumption of stationarity of the considered physiological variables. Moreover, standard estimates are unable to track time-varying changes in nonlinear coupling with high resolution in time. Here, we propose a novel definitio…
An Information-Theoretic Framework to Map the Spatiotemporal Dynamics of the Scalp Electroencephalogram
2016
We present the first application of the emerging framework of information dynamics to the characterization of the electroencephalography (EEG) activity. The framework provides entropy-based measures of information storage (self entropy, SE) and information transfer (joint transfer entropy (TE) and partial TE), which are applied here to detect complex dynamics of individual EEG sensors and causal interactions between different sensors. The measures are implemented according to a model-free and fully multivariate formulation of the framework, allowing the detection of nonlinear dynamics and direct links. Moreover, to deal with the issue of volume conduction, a compensation for instantaneous e…
Instantaneous Transfer Entropy for the Study of Cardiovascular and Cardio-Respiratory Nonstationary Dynamics
2017
Objective: Measures of transfer entropy (TE) quantify the direction and strength of coupling between two complex systems. Standard approaches assume stationarity of the observations, and therefore are unable to track time-varying changes in nonlinear information transfer with high temporal resolution. In this study, we aim to define and validate novel instantaneous measures of TE to provide an improved assessment of complex nonstationary cardiorespiratory interactions. Methods: We here propose a novel instantaneous point-process TE (ipTE) and validate its assessment as applied to cardiovascular and cardiorespiratory dynamics. In particular, heartbeat and respiratory dynamics are characteriz…
Lag-specific transfer entropy as a tool to assess cardiovascular and cardiorespiratory information transfer
2014
In the study of interacting physiological systems, model-free tools for time series analysis are fundamental to provide a proper description of how the coupling among systems arises from the multiple involved regulatory mechanisms. This study presents an approach which evaluates direction, magnitude, and exact timing of the information transfer between two time series belonging to a multivariate dataset. The approach performs a decomposition of the well-known transfer entropy (TE) which achieves 1) identifying, according to a lag-specific information-theoretic formulation of the concept of Granger causality, the set of time lags associated with significant information transfer, and 2) assig…
Effects of gender on resting leg blood flow: implications for measurement of regional substrate oxidation.
1998
Jensen, Michael D., Tu T. Nguyen, A. Hernández Mijares, C. Michael Johnson, and Michael J. Murray. Effects of gender on resting leg blood flow: implications for measurement of regional substrate oxidation. J. Appl. Physiol. 84(1): 141–145, 1998.—These studies were designed to examine whether the respiratory quotient (RQ) of leg tissue (primarily skeletal muscle) would increase to a greater degree in women than in men during meal ingestion. We found that mean leg and systemic RQ values were similar in men under both basal and fed conditions, whereas the agreement was poor in women. In women, leg RQ values tended to be greater than the systemic RQ, whereas splanchnic RQ values tended to be l…
Dynamics of the General Factor of Personality in Response to a Single Dose of Caffeine
2011
General Factor of Personality (GFP) research is an emergent field in personality research. This paper uses a theoretical mathematical model to predict the short-term effects of a dose of a stimulant drug on GFP and reports the results of an experiment showing how caffeine achieves this. This study considers the General Factor of Personality Questionnaire (GFPQ) a good psychometric approach to assess GFP. The GFP dynamic mechanism of change is based on the Unique Trait Personality Theory (UTPT). This theory proposes the existence of GFP which occupies the apex of the hierarchy of personality, and extends from an impulsiveness-and-aggressiveness pole (approach tendency) to an anxiety-andintro…