Search results for " Dynamics"
showing 10 items of 4108 documents
Exploratory Factor Analysis and Validation Study of the Lifetime Severity Index for Cocaine, Spanish Version (LSI-C-Spanish)
2007
The purpose of the study was to do an exploratory factor analysis and to examine the criterion-related and discriminant validity of the Lifetime Severity Index for Cocaine (LSI-C), Spanish version. A sample of 171 outpatients from 10 drug centers in Spain participated in the study. We conducted the factor analysis with orthogonal rotation and examined correlations between the LSI-C total score and criterion variables as well as the score obtained by a quality of life measure. The factor analysis revealed 2 principal factors that explain 65.8% of the variance. Lower LSI-C scores were associated with taking medication, receiving social help, using cocaine fewer than 30 times during the previo…
Mental representation of arm motion dynamics in children and adolescents.
2013
International audience; Motor imagery, i.e., a mental state during which an individual internally represents an action without any overt motor output, is a potential tool to investigate action representation during development. Here, we took advantage of the inertial anisotropy phenomenon to investigate whether children can generate accurate motor predictions for movements with varying dynamics. Children (9 and 11 years), adolescents (14 years) and young adults (21 years) carried-out actual and mental arm movements in two different directions in the horizontal plane: rightwards (low inertia) and leftwards (high inertia). We recorded and compared actual and mental movement times. We found th…
Acute effects of shock-type vibration transmitted to the hand-arm system.
1984
The aim of the project was to find out whether shock-type vibration of hand-tools compared to non-impulsive vibration has stronger acute effects on the hand-arm system and therefore needs a stricter evaluation from the occupational health point of view in comparison with the requirements of the Draft International Standard ISO-DIS 5349. Under laboratory conditions, subjects were exposed to simulated vibration of hand-tools (grinder, chain saw, hammer-drill, pneumatic hammer, rivet hammer and nailer). The following evaluation criteria were used: biomechanical transmissibility of the hand-arm system (wrist, elbow joint, shoulder joint); muscle-activity (m. flexor carpi ulnaris, m. biceps, m. …
Linear and nonlinear heart rate dynamics in elderly inpatients. Relations with comorbidity and depression
2010
Background. Hospitalization processes are known to increase depressive symptoms arising among elderly population. Meanwhile, dysregulation of cardiac autonomic function has been suggested to link depression and cardiovascular mortality. In this context, analysis of heart rate variability (HRV) is emerging as a powerful mortality risk stratifier clinical tool. The purpose of the study was to examine the relationship among HRV, depression, and comorbidity risk among an elderly inpatient population. Material and methods. Twenty-six subjects (aged 78±9 years) were recruited from the Short- Term Stay Unit at the Hospital General de Alicante. Before joining a Physical Activity Program aimed to pr…
Conditional Self-Entropy and Conditional Joint Transfer Entropy in Heart Period Variability during Graded Postural Challenge.
2015
Self-entropy (SE) and transfer entropy (TE) are widely utilized in biomedical signal processing to assess the information stored into a system and transferred from a source to a destination respectively. The study proposes a more specific definition of the SE, namely the conditional SE (CSE), and a more flexible definition of the TE based on joint TE (JTE), namely the conditional JTE (CJTE), for the analysis of information dynamics in multivariate time series. In a protocol evoking a gradual sympathetic activation and vagal withdrawal proportional to the magnitude of the orthostatic stimulus, such as the graded head-up tilt, we extracted the beat-to-beat spontaneous variability of heart per…
Unique sleep-stage transitions determined by obstructive sleep apnea severity, age and gender
2019
In obstructive sleep apnea, patients' sleep is fragmented leading to excessive daytime sleepiness and co-morbidities like arterial hypertension. However, traditional metrics are not always directly correlated with daytime sleepiness, and the association between traditional sleep quality metrics like sleep duration and arterial hypertension is still ambiguous. In a development cohort, we analysed hypnograms from mild (n = 213), moderate (n = 235) and severe (n = 277) obstructive sleep apnea patients as well as healthy controls (n = 105) from the European Sleep Apnea Database. We assessed sleep by the analysis of two-step transitions depending on obstructive sleep apnea severity and anthropom…
Uncertainty quantification in simulations of epidemics using polynomial chaos.
2012
Mathematical models based on ordinary differential equations are a useful tool to study the processes involved in epidemiology. Many models consider that the parameters are deterministic variables. But in practice, the transmission parameters present large variability and it is not possible to determine them exactly, and it is necessary to introduce randomness. In this paper, we present an application of the polynomial chaos approach to epidemiological mathematical models based on ordinary differential equations with random coefficients. Taking into account the variability of the transmission parameters of the model, this approach allows us to obtain an auxiliary system of differential equa…
A minimal limit-cycle model to profile movement patterns of individuals during agility drill performance: Effects of skill level.
2015
Identification of control strategies during agility performance is significant in understanding movement behavior. This study aimed at providing a fundamental mathematical model for describing the motion of participants during an agility drill and to determine whether skill level constrained model components. Motion patterns of two groups of skilled and unskilled participants (n = 8 in each) during performance of a forward/backward agility drill modeled as limit-cycles. Participant movements were recorded by motion capture of a reflective marker attached to the sacrum of each individual. Graphical and regression analyses of movement kinematics in Hooke’s plane, phase plane and velocity prof…
Mixed predictability and cross-validation to assess non-linear Granger causality in short cardiovascular variability series
2006
A method to evaluate the direction and strength of causal interactions in bivariate cardiovascular and cardiorespiratory series is presented. The method is based on quantifying self and mixed predictability of the two series using nearest-neighbour local linear approximation. It returns two causal coupling indexes measuring the relative improvement in predictability along direct and reverse directions, and a directionality index indicating the preferential direction of interaction. The method was implemented through a cross-validation approach that allowed quantification of directionality without constraining the embedding of the series, and fully exploited the available data to maximise th…
Time-Varying Surrogate Data to Assess Nonlinearity in Nonstationary Time Series: Application to Heart Rate Variability
2009
We propose a method to extend to time-varying (TV) systems the procedure for generating typical surrogate time series, in order to test the presence of nonlinear dynamics in potentially nonstationary signals. The method is based on fitting a TV autoregressive (AR) model to the original series and then regressing the model coefficients with random replacements of the model residuals to generate TV AR surrogate series. The proposed surrogate series were used in combination with a TV sample entropy (SE) discriminating statistic to assess nonlinearity in both simulated and experimental time series, in comparison with traditional time-invariant (TIV) surrogates combined with the TIV SE discrimin…