Search results for "Process"
showing 10 items of 22310 documents
Maintenance of marginal bone support and soft tissue esthetics at immediately provisionalized OsseoSpeed implants placed into extraction sites: 2-yea…
2012
Background Placement of implants into extraction sockets targets the maintenance of peri-implant hard and soft tissue structures and the support of a natural and esthetic contour. The main advantages of immediate implant insertion in comparison with delayed implant placement protocols are as follows: a reduced treatment time, less number of sessions, and, thus, the less invasive procedure. This study examines the clinical performance (survival rate, marginal bone levels and Pink Esthetic Score [PES]) of OsseoSpeed™ implants placed into extraction sockets with immediate provisionalization in the anterior maxilla after a follow-up of at least 12 months. Methods Twenty patients received a tota…
Epoch versus impulse models in the analysis of parametric fMRI studies
2013
Abstract Objective In parametric fMRI studies the relationship between the amplitude of the hemodynamic response and electrophysiological or behavioral parameters is commonly analyzed using the general linear model (GLM). We examined ways of using single-trial response time (RT) in the analysis of a decision-making task to better isolate task-specific activation. Methods fMRI and RT data were recorded in twenty-one subjects performing a visual-oddball-task. Four explanatory variables (EVs) were generated for the GLM-analysis: A conventional (constant impulse) EV, a constant epoch EV informed using subjects’ average RT, a variable impulse EV and a variable epoch EV both informed using single…
Redundant and synergistic information transfer in cardiovascular and cardiorespiratory variability
2015
In the framework of information dynamics, new tools are emerging which allow one to quantify how the information provided by two source processes about a target process results from the contribution of each source and from the interaction between the sources. We present the first implementation of these tools in the assessment of short-term cardiovascular and cardiorespiratory variability, by introducing two strategies for the decomposition of the information transferred to heart period (HP) variability from systolic arterial pressure (SAP) and respiration flow (RF) variability. Several measures based on the notion of transfer entropy (TE) are defined to quantify joint, individual and redun…
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…
Spinal Endocannabinoids and CB 1 Receptors Mediate C-Fiber–Induced Heterosynaptic Pain Sensitization
2009
Plastic Pain Perception Drugs and endocannabinoids acting on cannabinoid (CB) receptors have potential in the treatment of certain types of pain. In the spinal cord they are believed to suppress nociception, the perception of pain and noxious stimuli. Pernia-Andrade et al. (p. 760 ) now find that endocannabinoids, which are released in spinal cord by noxious stimulation, may promote rather than inhibit nociception by acting on CB1 receptors. Endocannabinoids not only depress transmission at excitatory synapses in the spinal cord, but also block the release of inhibitory neurotransmitters, thereby facilitating nociception.
Perceived collective burnout: a multilevel explanation of burnout
2011
Building up on the socially induced model of burnout and the job demands-resources model, we examine how burnout can transfer without direct contagion or close contact among employees. Based on the social information processing approach and the conservation of resources theory, we propose that perceived collective burnout emerges as an organizational-level construct (employees' shared perceptions about how burned out are their colleagues) and that it predicts individual burnout over and above indicators of demands and resources. Data were gathered during the first term and again during the last term of the academic year among 555 teachers from 100 schools. The core dimensions of burnout, ex…
Improved T2* assessment in liver iron overload by magnetic resonance imaging.
2009
In the clinical MRI practice, it is common to assess liver iron overload by T2* multi-echo gradient-echo images. However, there is no full consensus about the best image analysis approach for the T2* measurements. The currently used methods involve manual drawing of a region of interest (ROI) within MR images of the liver. Evaluation of a representative liver T2* value is done by fitting an appropriate model to the signal decay within the ROIs vs. the echo time. The resulting T2* value may depend on both ROI placement and choice of the signal decay model. The aim of this study was to understand how the choice of the analysis methodology may affect the accuracy of T2* measurements. A softwar…
Volumetry of Ventilated Airspaces by 3He MRI
2001
To develop a validated post-processing routine for volumetry of the ventilated airspaces by 3He MRI.3Helium MRI and pulmonary function tests were performed in seven healthy volunteers. After segmentation of ventilated airspaces, their volumes were calculated. Functional residual capacity (FRC) was used as a reference. For comparison of absolute volumes, correction factors were evaluated.Mean lung volume (+/- standard deviation) calculated from 3He MRI was 4,082 +/- 908 mL and mean FRC was 3,696 +/- 1166 mL, with a mean difference of 386 mL (r = 0.88). After correction for the relative pulmonary air content (factor 0.82), posture (0.72), and the individual tidal volume, 3He MRI volume was 3,…