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At least 919 records · Page 51Linked to original sources

PubMed2005

Drug-induced acute kidney injury.

PURPOSE OF REVIEW: The purpose of this review is to describe the most prevalent mechanisms of drug-induced acute kidney injury, to define the risk factors for nephrotoxicity, and to analyze the available evidence for preventive measures. RECENT FINDINGS: Drug toxicity remains an important cause of acute kidney injury that, in many circumstances, can be prevented or at least minimized by vigilance and early intervention. Recent studies have resulted in increased insight into the subcellular mechanisms of drug nephrotoxicity. Further improvement is to be expected from the identification of early markers of nephrotoxicity and an increasing involvement of a clinical pharmacist. SUMMARY: The main mechanisms of nephrotoxicity are vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis. Before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered. Modifiable risk factors should be corrected. The correct drug dosage should be prescribed. Patients should be pre-hydrated and the glomerular filtration rate should be frequently monitored during the administration of a potentially nephrotoxic drug. Studies are needed to further elucidate the mechanisms of nephrotoxicity to design more-rational prevention and treatment strategies. Computer-based prescriber-order entry and an appropriately trained intensive care unit pharmacist are particularly helpful to minimize medication errors and adverse drug events.

Acute Disease↗

PubMed2005

A general equation for estimating glomerular filtration rate from a single plasma sample.

OBJECTIVES: Glomerular filtration rate (GFR) may be estimated from a single plasma sample measurement using empirical equations. This method forms the basis of international guidelines on GFR measurement. New guidelines have recently been recommended by the British Nuclear Medicine Society (BNMS). These use the slope-intercept technique in which several samples are obtained. Quality control of measurement may be achieved by comparison with the individual single-sample values. This paper compares international guideline single-sample estimates of GFR with the new BNMS method and derives an improved general single-sample equation. METHODS: GFR measurements using Tc-DTPA were performed on 180 adults and 100 children using samples at approximately 2 h and 3 h and a further 45 adults with samples at 2, 3 and 4 h. The two-sample values obtained using the BNMS guideline method were compared to one-sample estimates obtained using (1) international guidelines and (2) a new equation derived from the data. The new equation was evaluated in a further 145 subjects. RESULTS: The international guidelines technique had systematic differences between the one-sample and two-sample estimates of GFR. The new equation had minimal systematic error and reduced random error (standard error of the estimate 4.5 ml . min per 1.73 m). CONCLUSIONS: There were significant differences between GFR values obtained using the international guidelines single-sample method and the slope-intercept method described in the BNMS guidelines. The new equation described in this paper gave considerably improved agreement and is recommended if single-sample estimates are to be used as quality control for BNMS guideline measurements.

Adult↗

PubMed2005

What have we learned about randomized, controlled trials in neonatal sepsis?

OBJECTIVE: To identify strategies to enable randomized, controlled trials in neonatal sepsis to recognize therapies that increase disability-free survival. METHODS: Rapid literature review. RESULTS: Randomized, controlled trials are the gold standard for testing a therapy because they minimize bias. However, randomized, controlled trials must also minimize random error if they are to detect moderate (and realistic) improvements in rates of disability-free survival reliably. This requires surprisingly large samples (i.e., thousands rather than hundreds). Against this perspective, most neonatal trials have been too small to be conclusive, so most neonatal therapies remain incompletely evaluated. As in specialties like cardiology and obstetrics, achieving reliable trials in neonatal sepsis will require international collaboration, simpler data sets, more cost-effective recruitment strategies, less exclusive criteria for selecting collaborators and patients, and an appreciation by clinicians and data-monitoring committees that substantially greater sample sizes are needed to limit the play of chance. Prospective meta-analysis using individual patient data is a promising strategy. It requires researchers to obtain funding from their national agencies to conduct similar trials according to an agreed protocol with prespecified hypotheses, interventions, power calculations, data sets, and measures of outcome. Prospective meta-analysis combines the methodologic advantages of a single "megatrial" with the practical advantages that financial burdens are spread internationally and different national funding cycles can be more flexibly accommodated. CONCLUSIONS: Prospective meta-analysis using individual patient data is a promising strategy for achieving large-scale, randomized evidence in neonatal sepsis.

Critical Illness↗

PubMedDate not supplied

Evaluation of CT scans and 3-D reformatted images for quantitative assessment of the hip.

Hip measurements using three-dimensional (3-D) images and computed tomography (CT) scans were evaluated. The 3-D measurements proved more accurate than CT measurements of femoral and acetabular anteversion. Additionally, accurate 3-D measurements (> 99%) of the femoral neck-shaft angle were provided. Acetabular anteversion determinations by CT scans were systematically decreased as pelvic flexion increased, whereas accuracy was > 96% with 3-D images. The 3-D software allows image rotation in all three reference planes, which minimizes positional errors. A case study is provided to exemplify the shortcomings of conventional imaging techniques and the utility of the quantitative 3-D protocol.

Cadaver↗

PubMed2001

Generation of a high-density rat EST map.

We have developed a high-density EST map of the rat, consisting of >11,000 ESTs. These ESTs were placed on a radiation hybrid framework map of genetic markers spanning all 20 rat autosomes, plus the X chromosome. The framework maps have a total size of approximately 12,400 cR, giving an average correspondence of 240 kb/cR. The frameworks are all LOD 3 chromosomal maps consisting of 775 radiation-hybrid-mapped genetic markers and ESTs. To date, we have generated radiation-hybrid-mapping data for >14,000 novel ESTs identified by our Rat Gene Discovery and Mapping Project (http://ratEST.uiowa.edu), from which we have placed >11,000 on our framework maps. To minimize mapping errors, ESTs were mapped in duplicate and consensus RH vectors produced for use in the placement procedure. This EST map was then used to construct high-density comparative maps between rat and human and rat and mouse. These maps will be a useful resource for positional cloning of genes for rat models of human diseases and in the creation and verification of a tiling set of map order for the upcoming rat-genome sequencing.

Animals↗

PubMed2006

Inverse method for the determination of a mathematical expression for the anisotropy of the solid-liquid interfacial energy in Al-Zn-Si alloys.

An expression for the anisotropy of the solid-liquid interfacial energy has been determined experimentally by an inverse method for the Al-43.4 wt%Zn-1.6 wt%Si system. Assuming that dendrite growth directions correspond to the minima of the surface stiffness, the anisotropy of the solid-liquid interfacial energy could be described by minimizing the errors between the calculated minima of a parametric interface stiffness function and experimentally measured growth directions of dendrites in thin coatings. In order to adequately describe the interfacial energy, it is found that a cubic harmonic expansion up to the third order is necessary to obtain the minima of interface stiffness along directions that depart from <100> or <110>. Best agreement with observed growth directions is obtained for first, second, and third harmonic coefficients (epsilon1, epsilon2, and epsilon3, respectively) satisfying the following relationships: epsilon2/epsilon1 = -0.188; epsilon3/epsilon1 = -0.00776. The corresponding interface stiffness function shows 24 minima lying along directions between <100> and <110>. The minima are located at 28.5 degrees from <100> and only 5.1 degrees from <320>, which was the growth direction suggested by Sémoroz for this alloy [A. Sémoroz, Y. Durandet, and M. Rappaz, Acta Mater. 49, 529 (2001).]. It was also found that the strength of the effective in-plane anisotropy is directly reflected by the morphology of the dendritic microstructure.

Journal Article↗

PubMed1979

Guard cell starch concentration quantitatively related to stomatal aperture.

Using quantitative histochemical techniques, the carbohydrate levels of guard cells from open and closed stomatal apparatus of Vicia faba L. were compared. To minimize experimental error, all comparisons were between leaflets of the same pair. Stomata on one leaflet were caused to open by light and reduced CO(2). The other leaflet, which was in darkness, had closed stomata. In one experiment, data were also collected on palisade parenchyma, spongy parenchyma, and epidermal cells.Guard cell starch concentration was higher in the leaflets with closed stomata than in open stomata by 72 +/- 16 millimoles per kilogram dry weight (anhydroglucosyl equivalents) (N = 117, P < 0.02). Variation in guard cell starch concentration from one part of a leaflet to another was small. The data are consistent with the hypothesis that starch degradation provides the carbon skeletons for anion synthesis in guard cells during stomatal opening.Sucrose concentration was higher in guard cells when stomata were open than when they were closed in all three experiments (average difference = 45 +/- 7 millimoles per kilogram dry weight [N = 59, P < 0.01]). The variability of sucrose concentration within test leaflets prevented an unequivocal interpretation of these results. When all data are considered, it appears that soluble sugars increase in guard cells when stomata of Vicia faba open.

Journal Article↗

PubMed1994

Continuous current source inversion of evoked potential fields in a spherical model head.

This study explores the efficacy of a physiological constraint on cortical current generators in promoting a robust solution for the inverse problem in evoked potentials. It is proposed that the current sources responsible for the evoked potential be modeled as a set of dipoles oriented orthogonal to the surface of the cortex. Rather than using a minimum norm approach, the solution space is searched for a vector that minimizes the error of the predicted evoked potential scalp field.

Animals↗

PubMed1990

Low-pass differentiators for biological signals with known spectra: application to ECG signal processing.

Digital low-pass filtering and differentiation (LPD) are useful in real-time processing of many biomedical signals. A general method is presented for determining the coefficients of a differentiator that maximizes the signal-to-noise ratio or minimizes the error between actual and ideal LPD filters, when signal and noise spectra are known. Several examples of digital filters suitable for QRS complex and P-T wave processing in ECG are presented.

Electrocardiography↗

PubMed2000

Regional head tissue conductivity estimation for improved EEG analysis.

We develop a method for estimating regional head tissue conductivities in vivo, by injecting small (1-10 microA) electric currents into the scalp, and measuring the potentials at the remaining electrodes of a dense-array electroencephalography net. We first derive analytic expressions for the potentials generated by scalp current injection in a four-sphere model of the human head. We then use a multistart downhill simplex algorithm to find regional tissue conductivities which minimize the error between measured and computed scalp potentials. Two error functions are studied, with similar results. The results show that, despite the low skull conductivity and expected shunting by the scalp, all four regional conductivities can be determined to within a few percent error. The method is robust to the noise levels expected in practice. To obtain accurate results the cerebrospinal fluid must be included in the forward solution, but may be treated as a known parameter in the inverse solution.

Action Potentials↗

PubMed1991

Control of the cryosurgical process in nonideal materials.

A study of a controlled cryosurgical process is presented. This study is based on the energy equations describing the probe response and the phase change occurring in the medium. First-order nonlinear differential equations (state equations) are obtained by applying the integral-solution method. In order to obtain maximal cell destruction, it is desired to control a specific cooling rate at the solid-liquid interface. This cooling rate defines the desired trajectories of the state variables through the state equations. In order to satisfy the cooling rate condition on the freezing front, a closed-loop is designed to control the probe temperature program. A simple analysis of the system stability employed linearization at several points along the desired trajectories. Ranges of stability were obtained for a system containing a proportional-integral controller. It was demonstrated that these stability ranges depend mainly on the selected sampling time of the discrete control loop and that the phase-change process does not significantly affect the stability results. A complete study of the nonlinear equations was performed by a computer simulation program which enables the selection of the final values of the controller parameters, in order to minimize the error and to ensure stability. In addition, the simulation program gives information about the effects of the A/D and D/A converters accuracy on the performance of the control loop. An A/D converter accuracy of 12 bits was found necessary in order to reduce the oscillations in probe temperature to acceptable values. The simulation also yields a complete calculated temperature field in the tissue during the controlled process. From these simulated results it can be seen that oscillations of +/- 0.5 degrees C in the desired probe temperature do not significantly affect the desired cooling rate at the freezing front. An initial overshoot of 1.5 degrees C in the desired probe temperature was obtained both experimentally and theoretically from the simulation. When this initial overshoot occurs at the beginning of the freezing process, it causes an error in freezing front velocity and consequently in ice-front position. From the numerical simulation, it can be deduced that the cooling rate obtained at the front deviates from the desired value by approximately 1%. The probe-temperature error increases at two instants: a) during the super-cooling effect and the subsequent sudden crystallization, and b) when the probe temperature is below -80 degrees C and unstable boiling of the cooling medium causes oscillations.

Cryosurgery↗

PubMed2002

In-vivo measurement of swine myocardial resistivity.

We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1 Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 ohm x cm at 1 Hz down to 166 ohm x cm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites.

Animals↗

PubMed2005

Three-dimensional trajectory assessment of an IVUS transducer from single-plane cineangiograms: a phantom study.

The recovery of the three-dimensional (3-D) path of the transducer used during an intravascular ultrasound (IVUS) examination is of primary importance to assess the exact 3-D shape of the vessel under study. Traditionally, the reconstruction is done by simply stacking the images during the pullback, or more recently using biplane angiography to recover the vessel curvature. In this paper, we explain, how single-plane angiography can be used with two projection models, to perform this task. Two types of projection geometry are analyzed: weak-perspective and full-perspective. In weak-perspective projection geometry, the catheter path can be reconstructed without prior transducer depth information. With full-perspective projection geometry, precise depth location of reference points are needed in order to minimize the error of the recovered transducer angle of incidence. The transducer angulation reconstruction is based on the foreshortening effect as seen from the X-ray images. By comparing the measured to the true transducer length, we are able to get its incidence angle. The transducer trajectory is reconstructed by stitching together the different estimated angulations obtained from each image in a cineangiogram sequence. The method is described and validated on two helical vessel phantoms, giving on average a reconstructed path that is less than 2 mm distant from the true path when using full-perspective projection.

Catheterization↗

PubMed2005

Quantifying motion in video recordings of neonatal seizures by robust motion trackers based on block motion models.

This paper introduces a methodology for the development of robust motion trackers for video based on block motion models. According to this methodology, the motion of a site between two successive frames is estimated by minimizing an error function defined in terms of the intensities at these frames. The proposed methodology is used to develop robust motion trackers that rely on fractional block motion models. The motion trackers developed in this paper are utilized to extract motor activity signals from video recordings of neonatal seizures. The experimental results reveal that the proposed motion trackers are more accurate and reliable than existing motion tracking methods relying on pure translation and affine block motion models.

Algorithms↗

PubMed2006

Feature extraction using information-theoretic learning.

A classification system typically consists of both a feature extractor (preprocessor) and a classifier. These two components can be trained either independently or simultaneously. The former option has an implementation advantage since the extractor need only be trained once for use with any classifier, whereas the latter has an advantage since it can be used to minimize classification error directly. Certain criteria, such as Minimum Classification Error, are better suited for simultaneous training, whereas other criteria, such as Mutual Information, are amenable for training the feature extractor either independently or simultaneously. Herein, an information-theoretic criterion is introduced and is evaluated for training the extractor independently of the classifier. The proposed method uses nonparametric estimation of Renyi's entropy to train the extractor by maximizing an approximation of the mutual information between the class labels and the output of the feature extractor. The evaluations show that the proposed method, even though it uses independent training, performs at least as well as three feature extraction methods that train the extractor and classifier simultaneously.

Algorithms↗

PubMed2005

Quantum 1/f effect in resonant biochemical piezoelectric and MEMS sensors.

Piezoelectric sensors used for the detection of chemical agents and as electronic nose instruments are based on bulk and surface acoustic wave resonators. Adsorption of gas molecules on the surface of the polymer coating is detected by a reduction of the resonance frequency of the quartz disk, subject also to fundamental quantum 1/f frequency fluctuations. The quantum 1/f limit of detection is given by the quantum 1/f formula for quartz resonators. Therefore, for quantum 1/f optimization and for calculation and improvement of the fundamental sensitivity limits, we must avoid closeness of the crystal size to the phonon coherence length, which corresponds to the maximum error and minimal sensitivity situation, as shown here. Adsorbed masses below the pg range can be detected. Microelectromechanical system (MEMS) resonators have provided a possibility for the nanominiaturization of these sensors. Essential for integrated nanotechnology, these resonant silicon bars (fingers) are excited magnetically or electrically through external applied forces, since they are not piezoelectric or magnetostrictive. The application of the quantum 1/f theory to these systems is published here for the first time. It provides simple formulas that yield much lower quantum 1/f frequency fluctuations for magnetic excitation, in comparison with electrostatically driven MEMS resonators.

Journal Article↗

PubMed2005

Iterative partial least squares with right-censored data analysis: a comparison to other dimension reduction techniques.

In the linear model with right-censored responses and many potential explanatory variables, regression parameter estimates may be unstable or, when the covariates outnumber the uncensored observations, not estimable. We propose an iterative algorithm for partial least squares, based on the Buckley-James estimating equation, to estimate the covariate effect and predict the response for a future subject with a given set of covariates. We use a leave-two-out cross-validation method for empirically selecting the number of components in the partial least-squares fit that approximately minimizes the error in estimating the covariate effect of a future observation. Simulation studies compare the methods discussed here with other dimension reduction techniques. Data from the AIDS Clinical Trials Group protocol 333 are used to motivate the methodology.

Anti-HIV Agents↗

PubMed2004

Reproducibility of patch test results: a concurrent right-versus-left study using TRUE Test.

Wide variations in the reproducibility rate of positive patch test responses have been reported. We hypothesized that a major source of non-reproducibility resides in the methodological pitfalls of routine patch testing. Simultaneous duplicate patch testing on opposite sides of the upper back was performed on 500 consecutive patients, using the TRUE Test system consisting of 2 panels, each one containing 12 standard allergens. A rigorous methodological design was applied and relevance was assessed for all discordant patch test reactions. A total of 435 positive patch test reactions were observed either on one or both sides in 289 patients (58.8%). Of these, 22 (5%) were discordant, i.e. interpreted as positive allergic on one side whilst negative or doubtful on the opposite side. The allergens responsible for discordant reactions were nickel sulfate (4 patients), cobalt chloride (3), lanolin alcohol (3), fragrance mix (2), carba mix (2), thiuram mix (2), colophonium (1), potassium dichromate (1), p-phenylenediamine (1), formaldehyde (1), balsam of Peru (Myroxylon pereirae resin) (1) and thimerosal (1). Of the 19 (4%) patients with discordant patch test reactions, the allergen was deemed to be of definite present or past relevance in 9 patients (1.8% of the total and 3.1% of all patients with positive patch test reactions) and of possible relevance in a further 2 patients. These data suggest that patch testing is a reasonably reproducible procedure as long as methodological error is minimized.

Adolescent↗