130,366 research outputs found
Principal component analysis of the t-wave for mortality Prediction in hemodialysis patients.
No full textPRINCIPAL COMPONENT ANALYSIS OF THE T-WAVE FOR MORTALITY
PREDICTION IN HEMODIALYSIS PATIENTS
Patients undergoing hemodialysis (HD) therapy often experience alterations in cardiac excitability and
have accounting for an estimated 3-year cumulative probability of cardiovascular death of 39.5% of
total deaths [1]. Abnormalities in ventricular repolarization and its dispersion could be a cause of HD-induced
arrhythmogenic effect.
Nowadays, no ECG-derived parameter has been proven to predict the risk of cardiovascular death.
QT dispersion (QTd) has been proposed, however, some concerns have been raised about uncertainty
of the QT dispersion measurement and technical difficulties in measuring the QT interval.
Principal component analysis (PCA) of the T-wave vector applied to 12-lead recordings has been
proposed to obtain an ECG marker of vulnerability to ventricular arrhythmias and of cardiovascular
mortality [2]. Several studies showed that the ratio of the second to first eigenvalues (PCA ratio) more
accurately represents repolarization abnormalities than QTd in a large general population sample [3,4].
The aim of this study was to explore the predictive value of the PCA ratio parameter for all-cause and
cardiac mortality in a retrospective study on HD patients.
METHODS
The selected subjects were 122 patients (46 women and 76 men, mean age 77±10) in whom digital
ECG recordings were available for the analysis from previous clinical studies. Standard holter 12-lead
recordings (H-12 Holter, Mortara Instrument Inc., Milwaukee, Wisconsin, USA) were collected
starting with the dialysis session. ECGs were sampled at 180 Hz or 1kHz and stored to a PC hard disk
for subsequent analysis.
PCA is an established method for representing data and, when applied to T-wave, it describes features
of repolarization in a manner that is less dependent on precise determination of T-wave offset.
Singular value decomposition was applied to the covariance matrix of the raw ECG data
corresponding to T-wave from the eight independent ECG leads. Then, the main eigenvectors of the
spatial T-wave were computed. The first eigenvector accounts for most of the energy in repolarization
when applied to the normal T-wave vector, whereas inhomogeneous repolarization, if present, is
indicated by a relevant contribution of the second and third components. Thus, the ratio of the second
to first eigenvalues of the spatial T-wave vector (PCA ratio) generated from the 12-lead digital ECG
serves as a measure of T-wave complexity or
heterogeneity of repolarization, with
increasing values referring to higher amount
of complexity. As shown in fig. 1 the PCA
ratio provides information that can be
visualized by analogy as the long and short
axes of the three-dimensional T-wave loop
and provides an estimate of the relative
fatness of the T-wave loop relative to its peak
amplitude, in which a fatter loop with a
higher PCA ratio reflects more complex Twave
morphology.
A median value of PCA was computed for
each patient throughout the whole ECG
recording. Following the Strong Heart Study
[3] a threshold for PCA ratio in men and
women, independently of gender, was
defined as 28%. Deaths were identified in an ongoing surveillance in each dialysis center and were
verified through review of medical records. Deaths were classified as cardiac if caused by myocardial
infarction, sudden death from CHD, or congestive heart failure by an independent review panel of
physicians unaware of PCA ratio findings. After a maximum follow-up of 5 years, patients were
censored as dead or alive considering the days from the date of the first ECG recording. Patients were
then divided in two groups depending on the median PCA ratio value. Endpoints were all-cause
mortality and cardiac mortality.
Mortality rates were calculated and plotted according to the Kaplan-Meier analysis. P<0.05 was
considered significant.
RESULTS AND DISCUSSION
During the fo..
Effects of Ca2+ and K+ Changes During Hemodialysis on Ventricular Repolarization Duration: in vivo and in silico Analysis.
No full textMETHOD FOR CLUSTERING HEMODIALYSIS (HD) PATIENTS BASED ON THE ESTIMATED WATER REFILLING INDEX (WRI).
No full textQT interval prolongation during haemodialysis (HD): in vivo and in silico analysis of the role of Ca2+ and K+ changes.
No full textMeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
METODO PER IDENTIFICARE GRUPPI DI PAZIENTI IN EMODIALISI (HD) BASATO SULLA STIMA DEL PARAMETRO WATER REFILLING INDEX (WRI)
No full text
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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