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Results for “Model performance”

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At least 523 records · Page 29Linked to original sources

PubMed2003

A new "TRISS-like" probability of survival model for intubated trauma patients.

BACKGROUND: Prehospital trauma patient field intubations and paralyzations, using neuromuscular blocking agents before emergency department respiratory and neurologic assessments are made, bias assessments and outcome evaluations using probability-of-survival models, such as TRISS and A Severity Characterization of Trauma (ASCOT). We present a newly developed "TRISS-like" probability-of-survival model for intubated blunt- and penetrating-injured patient assessment. METHODS: From a population of 51397 consecutively admitted trauma patients, this study used all 5740 (11.2% of the total injured population) intubated patients with complete data from a statewide trauma registry from October 1, 1993, to September 30, 1996. Model performance was evaluated using standard calibration and discrimination measures and z and W statistics of significance. RESULTS: The new model accurately predicted survival for blunt- and penetrating-injured intubated patients and is applicable to 11 etiologic patient populations. CONCLUSION: Study findings suggest that the new TRISS-like model should be used to assess both blunt- and penetrating-injured intubated patients. Use of this new model provides an analytical method for addressing a significant limitation of both the standard TRISS and ASCOT models, which are not applicable to intubated injured patient assessment. In addition, use of this model will complement TRISS/ASCOT assessments of nonintubated trauma patients and thus permit appropriate assessments for both intubated and nonintubated injured patient study populations.

Adolescent↗

PubMed2006

A system model of oral glucose absorption: validation on gold standard data.

A reliable model of glucose absorption after oral ingestion may facilitate simulation as well as pathophysiological studies. One of the difficulties for the development and quality assessment of such models has been the lack of gold standard data for their validation. Thus, while data on plasma concentrations of glucose are available, the rates of appearance in plasma of ingested glucose (Ra) were not available to develop such models. Here we utilize the recent availability of Ra data, estimated with a model-independent multiple tracer technique, to formulate a system model of intestinal glucose absorption. Two published and two new models are tested on this new data set. One of the two new models performed best: it is nonlinear, describes the Ra data well and its parameters are estimated with good precision. This model has important potential both in simulation contexts, e.g., it can be incorporated in whole-body models of the glucose regulatory system, as well as in physiological and clinical studies to quantitatively characterize possible impairment of glucose absorption in particular populations such as elderly and diabetic individuals.

Absorption↗

PubMed2003

Remote-sensing reflectance in the Beaufort and Chukchi seas: observations and models.

Two semianalytical remote-sensing reflectance models were evaluated and validated by use of bio-optical data collected in the Beaufort and Chukchi seas. Both models were efficient at retrieving chlorophyll concentration, phytoplankton absorption coefficients,and particulate backscattering coefficients. In contrast, they were not accurate in predicting an absorption coefficient for colored dissolved organic matter plus nonpigmented particulates. The poor model performance is attributed to the high variability in the concentrations of these colored materials. A chlorophyll-dependent reflectance model was also assessed, and it proved to be highly successful in reproducing measured reflectance spetra. A four-component, case 2 model with mean absorption spectra for phytoplankton, soluble materials, and nonpigmented particulates was employed in Hydrolight radiative-transfer model simulations. The remote sensing reflectance spectra simulated inthe radiative-transfer model were in excellent agreement with field data. The similarity between the model and the measurement confirms the accuracy of the underlying bio-optical relationships and underscores the utility of modeling for better understanding of the variability of ocean color observations. The latest SeaWiFS algorithm (OC4V4) overestimated chlorophyll by approximately 1.5 fold across most of the observed range of biomass (0.07-9 mg chlorophyll m(-3)). Regionally tuned algorithms explained > 93% of the variability in the surface chlorophyll concentration.

Journal Article↗

PubMed1981

The invariance of sentence performance structures across language modality.

Native users of American Sign Language were asked to manipulate sentences in four different ways: sign them at slow rate, parse them, make relatedness judgments of pairs of signs taken from each sentence, and recall the sentences. The data obtained from these four tasks (pause durations, parsing values, indices of relatedness and probe latencies) were used to construct hierarchical performance structures for each of the sentences. The resulting structures were highly similar across tasks; that is, performance structures are not task specific. The four measures at each sign boundary in each sentence were well predicted by a performance model, elaborated by Grosjean, Grosjean, and Lane for speech, that combines a parsing measure with a symmetry measure. Thus performance structures appear to be founded in the processing of language, be it visual or oral, and not in the properties of any particular communication modality.

Adult↗

PubMedDate not supplied

Effects of oxygen on aerobic solid-state biodegradation kinetics.

Oxygen is a critical control variable for composting and other solid-state biodegradation processes. In this study we examined the effect of varying oxygen concentrations (1%, 4%, and 21% O2 (v/v)) on biodegradation kinetics under different substrate (sewage sludge and synthetic food waste), temperature (35, 45, 55, and 65 degrees C), and moisture (36-60% H2O) conditions. Three forms of a saturation or Monod-type model and one form of an exponential model were evaluated against data from extensive experiments under carefully controlled environmental conditions. The exponential model performed well at temperatures from 35 to 55 degrees C but had problems at higher temperatures. The Monod-type models yielded the best fit based on R2 values. Multiple linear regression was used to express the oxygen half-saturation coefficient as a function of temperature and moisture. For a modified one-parameter saturation model the half-saturation coefficient varied from -0.67% to 1.74% v/v O2 under the range of conditions typical of composting systems. While the positive correlation of biodegradation rate with oxygen concentration reported by previous researchers held true for temperatures below 55 degrees C, an inverse relationship was found at 65 degrees C. Although this study did not directly examine anaerobic conditions, the results under microaerophilic conditions suggest oxygen may not offer kinetic advantages for extreme thermophilic biodegradation processes.

Biodegradation, Environmental↗

PubMed2000

Noninvasive blood glucose measurements by near-infrared transmission spectroscopy across human tongues.

Noninvasive blood glucose measurements are characterized in human subjects. A series of first overtone transmission spectra are collected across the tongues of five human subjects with type 1 diabetes. The noninvasive human spectra are collected by an experimental protocol that is designed to minimize chance correlations with blood glucose levels. In one treatment of the data, every fifth sample is used as a blind prediction point to validate model performance. In another rearrangement of the data, the spectra collected over the first 29 days are used to build calibration models that are then used to predict in vivo glycemia from spectra collected over the next 10 days. Of the five data sets (one for each subject), one demonstrates a complete inability to predict blood glucose levels and is deemed void of glucose-specific information. Glucose-specific information is evident in the remaining four data sets, albeit to varying degrees. For all data sets, the ability to measure glucose from spectra collected noninvasively from human subjects depends on spectral quality and reproducibility of the tongue-to-spectrometer interface. The standard error of prediction is 3.4 mM for the best calibration model. The significance of this magnitude of prediction error is discussed relative to the situations where: (1) the model is completely void of glucose-specific information and (2) glucose predictions are limited by spectral signal-to-noise and sample thickness. Overall, glucose-specific information is available from noninvasive first-overtone spectra collected across human tongues. Significant improvements are necessary, however, before clinically useful measurements are possible.

Blood Glucose↗

PubMed2006

Mixed models and empirical bayes estimation for retrospective exposure assessment of dust exposures in Canadian sawmills.

OBJECTIVES: Data on job histories is commonly available from study subjects and worksites, therefore jobs are often used for assigning exposures in historical epidemiological studies. Exposure estimates are often derived by offering jobs as fixed effects in statistical models. An alternative approach would be to offer job as a random effect to obtain empirical Bayes estimates of exposure. This approach is more efficient since it weights exposure estimates according to the within-job and between-job variability and the number of measurements for each job. We assess three models for predicting historical dust exposures of sawmill workers. METHODS: Models were developed using 407 inhalable dust measurements collected from 58 jobs in four sawmills. The first model incorporated all variables as fixed effects; the second added a random term to account for correlation within workers; and the third offered random terms for worker, job and mill (hierarchical model). Empirical Bayes estimates were used to calculate job-specific exposures from the hierarchical model. RESULTS: The fixed effects and random worker mixed models performed nearly identically because there was low within-worker correlation (r = 0.26). The Bayesian exposure predictions from the hierarchical model were slightly more correlated with the observed mill-job arithmetic means than those from the models where jobs were fixed effects (0.74 versus 0.70). CONCLUSIONS: While we observed no large differences in exposure estimates by treating job as a fixed or random effect, treating job as a random effect allowed for job-specific coefficients to be estimated for every job while borrowing strength in the presence of sparse data by assuming that the job means are normally distributed around the group mean. In addition, empirical Bayes job estimates can be used for a posteriori job grouping. The use of this method for retrospective exposure assessment should continue to be examined.

Air Pollutants, Occupational↗

PubMed2003

Empirical models for substitution in ribosomal RNA.

Empirical models of substitution are often used in protein sequence analysis because the large alphabet of amino acids requires that many parameters be estimated in all but the simplest parametric models. When information about structure is used in the analysis of substitutions in structured RNA, a similar situation occurs. The number of parameters necessary to adequately describe the substitution process increases in order to model the substitution of paired bases. We have developed a method to obtain substitution rate matrices empirically from RNA alignments that include structural information in the form of base pairs. Our data consisted of alignments from the European Ribosomal RNA Database of Bacterial and Eukaryotic Small Subunit and Large Subunit Ribosomal RNA ( Wuyts et al. 2001. Nucleic Acids Res. 29:175-177; Wuyts et al. 2002. Nucleic Acids Res. 30:183-185). Using secondary structural information, we converted each sequence in the alignments into a sequence over a 20-symbol code: one symbol for each of the four individual bases, and one symbol for each of the 16 ordered pairs. Substitutions in the coded sequences are defined in the natural way, as observed changes between two sequences at any particular site. For given ranges (windows) of sequence divergence, we obtained substitution frequency matrices for the coded sequences. Using a technique originally developed for modeling amino acid substitutions ( Veerassamy, Smith, and Tillier. 2003. J. Comput. Biol. 10:997-1010), we were able to estimate the actual evolutionary distance for each window. The actual evolutionary distances were used to derive instantaneous rate matrices, and from these we selected a universal rate matrix. The universal rate matrices were incorporated into the Phylip Software package ( Felsenstein 2002. http://evolution.genetics.washington.edu/phylip.html), and we analyzed the ribosomal RNA alignments using both distance and maximum likelihood methods. The empirical substitution models performed well on simulated data, and produced reasonable evolutionary trees for 16S ribosomal RNA sequences from sequenced Bacterial genomes. Empirical models have the advantage of being easily implemented, and the fact that the code consists of 20 symbols makes the models easily incorporated into existing programs for protein sequence analysis. In addition, the models are useful for simulating the evolution of RNA sequence and structure simultaneously.

Amino Acid Substitution↗

PubMed2004

The control of copy number of IS6110 in Mycobacterium tuberculosis.

Insertion sequence (IS) elements are bacterial genes that are able to transpose to different locations in the genome. These elements are often used in molecular epidemiology as genetic markers that track the spread of pathogens. Transposable elements have frequently been described as "selfish DNA" because they facilitate their own transposition, causing damage when they insert into coding regions, while contributing little if anything to the bacterial host. According to this hypothesis, the expansion of copy number of insertion sequences is opposed by negative selection against high copy numbers. From an alternative point of view, we might expect IS elements to intrinsically regulate transposition within cells, thereby limiting damage to their bacterial host. Here, we report evidence that the copy number of IS6110 in Mycobacterium tuberculosis is controlled by selection against the element. We first construct 12 different models of marker change resulting from a combination of possible transposition functions and selective regimes. We then compute the Akaike Information Criterion for each model to identify the models that best explain data consisting of serial isolates of M. tuberculosis genotyped with IS6110. We find that the best performing models all include selection against the accumulation of copies. Specifically, our analysis points to the interaction of separate copies of the element causing lethal effects. We discuss the implications of these findings for genome evolution and molecular epidemiology.

DNA Transposable Elements↗

PubMed2025

Examining Transcriptomic Markers Associated With Neutrophil Extracellular Traps to Predict Mortality Risk in Neonatal Sepsis.

BACKGROUND: Neonates are highly susceptible to sepsis, which is often accompanied by fatal coagulopathy. Anticoagulant therapies have not reduced sepsis-related mortality in clinical trials, possibly due to patient heterogeneity. Neutrophil extracellular traps (NETs) enhance coagulation by activating platelets, suggesting that NET-specific biomarkers may identify patients who may benefit from targeted anticoagulant treatment. This study evaluated the association between NET gene expression and adverse outcomes in neonatal sepsis. METHODS: We analyzed whole blood transcriptomes from 123 neonates with sepsis and developed a predictive model, the NET score, based on NET-related gene expression. Model performance was assessed in two independent validation sets. Mediation and correlation analyses explored the relationship between the NET score and a coagulation score. Temporal transcriptomic data from septic shock cases further tested this interaction. RESULTS: The NET score achieved AUCs of 88.7% and 85.4% in validation Sets 1 and 2, respectively, indicating strong predictive performance. Mediation and temporal analyses supported a sequential relationship between NETosis and coagulation in sepsis. Age-specificity of the model was confirmed using pediatric (n = 163) and adult (n = 86) sepsis transcriptomic datasets. Neonates with disseminated intravascular coagulation exhibited a trend toward elevated NET scores. CONCLUSIONS: Our findings support a novel risk stratification approach using the NET score to identify neonates at increased risk for sepsis-associated coagulopathy and poor outcomes, potentially guiding targeted therapeutic strategies.

neonatal sepsis↗

PubMed2005

Comparison of coding of heart failure and comorbidities in administrative and clinical data for use in outcomes research.

BACKGROUND: Despite the potential usefulness of administrative databases for evaluating outcomes, coding of heart failure and associated comorbidities have not been definitively compared with clinical data. OBJECTIVE: To compare the predictive value of heart failure diagnoses and secondary conditions identified in a large administrative database with chart-based records. METHODS: The authors studied 1808 patient records sampled from 14 acute care hospitals and compared clinically recorded data with administrative records from the Canadian Institute for Health Information. The impact of comorbidity coding in the administrative data set according to the Charlson classification was examined in models of 30-day mortality. RESULTS: The positive predictive value (PPV) of a primary diagnosis ICD-9 428 was 94.3% using the Framingham criteria and 88.6% using criteria previously validated with pulmonary capillary wedge pressure. There was reduced prevalence of secondary comorbid conditions in administrative data in comparison with clinical chart data. The specificities and PPV/negative predictive values of administratively identified index comorbidities were high. The sensitivities of index comorbidities were low, but were enhanced by examination of hospitalizations within 1 year prior to the index heart failure admission. Using information from prior hospitalizations modestly enhanced 30-day mortality model performance; however, the odds ratio point estimates of the index and enhanced administrative data sets were consistent with the clinical model. CONCLUSION: The ICD-9 428 primary diagnosis is highly predictive of heart failure using clinical criteria. Examination of hospitalization data up to 1 year prior to the index admission improves comorbidity detection and may provide enhancements to future studies of heart failure mortality.

Aged↗

PubMed1998

A computational role for dopamine delivery in human decision-making.

Recent work suggests that fluctuations in dopamine delivery at target structures represent an evaluation of future events that can be used to direct learning and decision-making. To examine the behavioral consequences of this interpretation, we gave simple decision-making tasks to 66 human subjects and to a network based on a predictive model of mesencephalic dopamine systems. The human subjects displayed behavior similar to the network behavior in terms of choice allocation and the character of deliberation times. The agreement between human and model performances suggests a direct relationship between biases in human decision strategies and fluctuating dopamine delivery. We also show that the model offers a new interpretation of deficits that result when dopamine levels are increased or decreased through disease or pharmacological interventions. The bottom-up approach presented here also suggests that a variety of behavioral strategies may result from the expression of relatively simple neural mechanisms in different behavioral contexts.

Cerebral Cortex↗

PubMed2002

Ontogeny of hepatic and renal systemic clearance pathways in infants: part II.

Maturation of drug systemic clearance mechanisms during the postnatal period produces dramatic and rapid changes in an infant's capacity to eliminate drugs. A tentative general mathematical model describing the ontogeny of hepatic cytochrome P450 (CYP) enzyme-mediated clearance and renal clearance due to glomerular filtration in the first 6 months of life was elaborated from age-specific in vitro hepatic microsomal activity data (normalised to amount of hepatic microsomal protein) for enzyme-specific probe substrates and in vivo probe substrate data for glomerular filtration (normalised to bodyweight), respectively. The model predicts an age- and clearance pathway-specific Infant Scaling Factor (ISF) for the first 6 months of life. The ISF reflects functional maturation of a specific clearance pathway (normalised to bodyweight) relative to adult values. Therefore, the ISF directly correlates adult clearance values with an infant's capacity to eliminate drugs. Substitution of appropriate model parameter estimates and the age of the infant into the model provides an estimated ISF value, which may then be used to predict the contribution of a particular clearance pathway to total systemic clearance in the infant when adult systemic clearance values are known. The model was tested for its ability to predict infant systemic clearance of drugs whose elimination is principally mediated by a single CYP enzyme or by glomerular filtration. The model performed reasonably well for CYP1A2 and CYP3A4, but poorer predictions were obtained for CYP2D6 and CYP2C because of lack of model complexity and/or inadequate hepatic microsomal activity data to fully describe the maturational process of functional enzyme. For renal clearance due to glomerular filtration, data normalised to bodyweight (kg) showed a limited maturational trend, suggesting that adult renal clearances normalised to bodyweight might reasonably predict infant renal clearances in the first 6 months of life. The model provided reasonable predictions of renal clearance due to glomerular filtration in the infant.

Cytochrome P-450 Enzyme System↗

PubMed2001

Modeling the postural disturbances caused by upper extremity movements.

This paper describes the design, validation, and application of a dynamic, three-dimensional (3-D) model of the upper extremity for the purpose of estimating postural disturbances generated by movements of the arms. The model consists of two links representing the upper and lower arms, with the shoulder and elbow modeled as gimbal joints to allow three rotational degrees of freedom. With individualized segment inertial parameters based on anthropometric measurements, the model performs inverse dynamic analysis of recorded arm movements to calculate reaction forces and moments acting on the body at the shoulder in three dimensions. The method was validated by comparing the output of the model to estimates obtained from ground reaction loads during stereotypical and free form unilateral movements at various velocities and with different loads carried by human subjects while seated on biomechanical force platforms. The correlation between predicted and measured reaction forces and moments was very good under all conditions and across all subjects, with average rms errors less than 8% of measured peak-to-peak values. The model was then applied to bimanual activities representative of functional movements that would typically be performed while standing at a counter. The resulting estimates were consistent and adequate for the purpose of evaluating postural disturbances caused by upper extremity movements.

Adult↗

PubMed1992

Monte Carlo modelling of the performance of a rotating slit-collimator for improved planar gamma-camera imaging.

Planar imaging with a gamma camera is currently limited by the performance of the collimator. Spatial resolution and sensitivity trade off against each other; it is not possible with conventional parallel-hole collimation to have high geometric sensitivity and at the same time excellent spatial resolution unless field-of-view is sacrificed by using fan- or cone-beam collimators. We propose a rotating slit-collimator which collects one-dimensional projections from which the planar image may be reconstructed by the theory of computed tomography. The performance of such a collimator is modelled by Monte Carlo methods and images are reconstructed by a convolution and backprojection technique. The performance is compared with that of a conventional parallel-hole collimator and it is shown that higher spatial resolution with increased sensitivity is possible with the slit-collimator. For a point source a spatial resolution of some 6 mm at a distance of 100 mm from the collimator with a x7 sensitivity compared with a parallel-hole collimator was achieved. Applications to bone scintigraphy are modelled and an improved performance in hot-spot imaging is demonstrated. The expected performance in cold-spot imaging is analytically investigated. The slit-collimator is not expected to improve cold-spot imaging. Practical design considerations are discussed.

Equipment Design↗

PubMed2005

Finite-element modeling of the anthropoid mandible: the effects of altered boundary conditions.

Finite-element modeling provides a full-field method for describing the stress environment of the skull. The utility of finite-element models, however, remains uncertain given our ignorance of whether such models validly portray states of stress and strain. For example, the effects of boundary conditions that are chosen to represent the mechanical environment in vivo are largely unknown. We conducted an in vitro strain gauge experiment on a fresh, fully dentate adult mandible of Macaca fascicularis to model a simplified loading regime by finite-element analysis for purposes of model validation. Under various conditions of material and structural complexity, we constructed dentate and edentulous models to measure the effects of changing boundary conditions (force orientation and nodal constraints) on strain values predicted at the gauge location. Our results offer a prospective assessment of the difficulties encountered when attempting to validate finite-element models from in vivo strain data. Small errors in the direction of load application produce significant changes in predicted strains. An isotropic model, although convenient, shows poor agreement with experimental strains, while a heterogeneous orthotropic model predicts strains that are more congruent with these data. Most significantly, we find that an edentulous model performs better than a dentate one in recreating the experimental strains. While this result is undoubtedly tied to our failure to model the periodontal ligament, we interpret the finding to mean that in the absence of occlusal loads, teeth within alveoli do not contribute significantly to the structural stiffness of the mandible.

Animals↗

PubMed2002

Prediction of duration of hospitalization in respiratory syncytial virus infection.

Identification of variables that predict duration of RSV-associated hospitalization may be useful in the identification of preventive and therapeutic strategies. A recently published prediction model (Michigan model) for the duration of hospitalization in RSV infection demonstrated good discrimination between children with and without an increased likelihood of a hospital stay >or= 7 days, based on variables such as log weight, congenital heart disease, failure to thrive, premature birth, bronchopulmonary dysplasia, other pulmonary diseases, miscellaneous conditions, early mechanical ventilation, and early ribavirin treatment (receiver operating characteristic (ROC) area, 0.89). Validation of this model is of particular interest for Europe, since the mean duration of hospitalization in The Netherlands is approximately twice that in the USA. The objective of the current study was 1) to validate the Michigan model for RSV hospitalized patients in a large university hospital in The Netherlands, and 2) to develop our own prediction model for a prolonged hospital stay. Data from 177 children younger than 12 months of age admitted with confirmed RSV infection to the Sophia Children's Hospital Rotterdam between 1992-1995, were used for valiation of the Michigan model and derivation of the Rotterdam model. Mean duration of hospitalization for the Rotterdam database was 10.3 (+/-6.3) days, with a median of 9 days; 138 (78%) patients had a hospital stay >or= 7 days. The Michigan model performed poorly when applied to the Rotterdam database, with an ROC area of 0.65 (95% CI, 0.57-0.73). The Rotterdam prediction model (hospital stay >or= 9 days, the median in our database) considered weight and need for oxygen supplementation. The ROC area was 0.65 (95% CI, 0.57-0.73). When using data from patients for the 1995-1996 season, the ROC area was 0.52 (95% CI, 0.34-0.72). The Michigan and the Rotterdam models failed to identify a considerable number of patients who had a prolonged hospital stay, with a low false-positive rate. We conclude that neither the Michigan, nor the Rotterdam model reliably predicted the duration of hospitalization based on demographic and clinical variables.

Female↗

PubMed1992

Assessment of a model for overall left ventricular three-dimensional motion from MRI data.

In this paper we present a complete methodology to evaluate a model for overall three-dimensional (3D) motion of the human left ventricle (LV) from MRI data. The left ventricular motion is approximated by a linear model associated with an affine transformation to determine parameters for non-rigid motion of the LV. The proposed method has been applied to a normal patient and to a patient with cardiac disease. Results obtained show that the linear model provides a fairly good approximation of normal left ventricular motion, whereas serious cardiac disease produces abnormal motion, yielding altered model performances.

Heart Diseases↗