Search results for " Entropy"

Assessing Complexity in Physiological Systems through Biomedical Signals Analysis

2020

The idea that most physiological systems are complex has become increasingly popular in recent decades [...]

Discretising Keyfitz' entropy for studies of actuarial senescence and comparative demography

2023

1. Keyfitz’ entropy is a widely used metric to quantify the shape of the survivorship curve of populations, from plants, to animals, and microbes. Keyfitz’ entropy values 1 correspond to species with a decreasing mortality rate with age (negative senescence), and a Keyfitz entropy of exactly 1 corresponds to a constant mortality rate with age. Keyfitz’ entropy was originally defined using a continuous-time model, and has since been discretised to facilitate its calculation from discrete-time demographic data. 2. Here, we show that the previously used discretisation of the continuous-time metric does not preserve the relationship with increasing, decreasing, or constant mortality rates. To r…

Compensated transfer entropy as a tool for reliably estimating information transfer in physiological time series

2013

We present a framework for the estimation of transfer entropy (TE) under the conditions typical of physiological system analysis, featuring short multivariate time series and the presence of instantaneous causality (IC). The framework is based on recognizing that TE can be interpreted as the difference between two conditional entropy (CE) terms, and builds on an efficient CE estimator that compensates for the bias occurring for high dimensional conditioning vectors and follows a sequential embedding procedure whereby the conditioning vectors are formed progressively according to a criterion for CE minimization. The issue of IC is faced accounting for zero-lag interactions according to two a…

Analisi sperimentale di laboratorio sulla stima della velocità media del flusso mediante la teoria entropica

2014

Information-theoretic assessment of cardiovascular-brain networks during sleep

2015

This study was aimed at detecting the structure of the physiological network underlying the regulation of the cardiovascular and brain systems during normal sleep. To this end, we measured from the polysomnographic recordings of 10 healthy subjects the normalized spectral power of heart rate variability in the high frequency band (HF) and the EEG power in the δ, θ, α, σ, and β bands. Then, the causal statistical dependencies within and between these six time series were assessed in terms of internal information (conditional self entropy, CSE) and information transfer (transfer entropy, TE) computed via a linear method exploiting multiple regression models and a nonlinear method combining ne…

Information domain approach to the investigation of cardio-vascular, cardio-pulmonary, and vasculo-pulmonary causal couplings

2011

The physiological mechanisms related to cardio-vascular (CV), cardio-pulmonary (CP), and vasculo-pulmonary (VP) regulation may be probed through multivariate time series analysis tools. This study applied an information domain approach for the evaluation of non-linear causality to the beat-to-beat variability series of heart period (t), systolic arterial pressure (s), and respiration (r) measured during tilt testing and paced breathing (PB) protocols. The approach quantifies the causal coupling from the series i to the series j (C(ij)) as the amount of information flowing from i to j. A measure of directionality is also obtained as the difference between two reciprocal causal couplings (D(i…

2020

Gait variability observed in step duration is predictive of impending adverse health outcomes among apparently healthy older adults and could potentially be evaluated using wearable sensors (inertial measurement units, IMU). The purpose of the present study was to establish the reliability and concurrent validity of gait variability and complexity evaluated with a waist and an ankle-worn IMU. Seventeen women (age 74.8 (SD 44) years) and 10 men (73.7 (4.1) years) attended two laboratory measurement sessions a week apart. Their stride duration variability was concurrently evaluated based on a continuous 3 min walk using a force plate and a waist- and an ankle-worn IMU. Their gait complexity (…

AB0929 Balance in fibromyalgia is not related with lower limb strength

2017

Background Postural control, that depends on many sensory contributors and motor skills, is altered in people with fibromyalgia (FM) 1–3. Knowing those contributors that could be impaired in this population is important to design an appropriate balance therapy. Objectives Due to the fact that people with FM use to present a strength loss 7, our main goal was to explore the relation between postural control and lower limb strength in this population. Further, the sensory inputs contributors to the postural control were assessed. Methods A cross-sectional study was conducted in a sample of 40 FM patients. A force platform was used to assess postural control under five bipedal conditions: i) e…

Analysis of inter-atrium differences in paroxysmal and persistent atrial fibrillation using principal component analysis

2007

The pathophysiological mechanisms of atrial fibrillation (AF) are not entirely clear yet, and there is no full explanation for the development and evolution of the arrhythmia. The goal of this study is to find inter-atrium differences in electrophysiological behavior between persistent and paroxysmal AF. The database analyzed contains intra-cardiac records from 14 patients with paroxysmal AF and 10 with persistent AF. Dominant frequency and sample entropy measurements showed that in the paroxysmal group there was a left-to-right gradient. These differences were enhanced after the extraction of the main components with principal component analysis. These findings may be interpreted as a poss…

Wiener-Granger Causality in Network Physiology with Applications to Cardiovascular Control and Neuroscience

2016

Since the operative definition given by C. W. J. Granger of an idea expressed by N. Wiener, the Wiener–Granger causality (WGC) has been one of the most relevant concepts exploited by modern time series analysis. Indeed, in networks formed by multiple components, working according to the notion of segregation and interacting with each other according to the principle of integration, inferring causality has opened a window on the effective connectivity of the network and has linked experimental evidences to functions and mechanisms. This tutorial reviews predictability improvement, information-based and frequency domain methods for inferring WGC among physiological processes from multivariate…