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At least 145 records · Page 8Linked to original sources
PubMed2004

The applicability of a computer model for predicting head injury incurred during actual motor vehicle collisions.

BACKGROUND: Head injury is a significant cause of both morbidity and mortality. Motor vehicle collisions (MVCs) are the most common source of head injury in the United States. No studies have conclusively determined the applicability of computer models for accurate prediction of head injuries sustained in actual MVCs. This study sought to determine the applicability of such models for predicting head injuries sustained by MVC occupants. METHODS: The Crash Injury Research and Engineering Network (CIREN) database was queried for restrained drivers who sustained a head injury. These collisions were modeled using occupant dynamic modeling (MADYMO) software, and head injury scores were generated. The computer-generated head injury scores then were evaluated with respect to the actual head injuries sustained by the occupants to determine the applicability of MADYMO computer modeling for predicting head injury. RESULTS: Five occupants meeting the selection criteria for the study were selected from the CIREN database. The head injury scores generated by MADYMO were lower than expected given the actual injuries sustained. In only one case did the computer analysis predict a head injury of a severity similar to that actually sustained by the occupant. CONCLUSION: Although computer modeling accurately simulates experimental crash tests, it may not be applicable for predicting head injury in actual MVCs. Many complicating factors surrounding actual MVCs make accurate computer modeling difficult. Future modeling efforts should consider variables such as age of the occupant and should account for a wider variety of crash scenarios.

Accidents, Traffic↗
PubMed1997

Computer model generated density correction factors for gamma spectroscopy counting.

Using the calibration curve of a single reference source to infer activity levels in samples of different bulk density and/or elemental composition may yield inaccurate results by a gamma spectroscopy system. These inaccuracies are magnified when counting low energy photons, which interact primarily through the photoelectric effect. There have been numerous methods described to empirically derive density correction factors for various samples. An alternate solution is to theoretically derive density correction factors using a computer model. The computer model generated density correction factors for material such as sand, ilmenite, and polyester are in close agreement with published empirically derived density correction factors for these same materials.

Americium↗
PubMed2002

Pretest prediction of BRCA1 or BRCA2 mutation by risk counselors and the computer model BRCAPRO.

BACKGROUND: Because BRCA gene mutation testing is costly, occasionally uninformative, and frequently associated with ethical and legal issues, careful patient selection is required prior to testing. Estimation of BRCA gene mutation probability is an important component of pretest counseling, but the accuracy of these estimates is currently unknown. We measured the performance of eight cancer risk counselors and of a computer model, BRCAPRO, at identifying families likely to carry a BRCA gene mutation. METHODS: Eight cancer risk counselors and the computer model BRCAPRO estimated BRCA gene mutation probabilities for 148 pedigrees selected from an initial sample of 272 pedigrees. The final sample was limited to pedigrees with a proband affected by breast or ovarian cancer and BRCA1 and BRCA2 gene sequencing results unequivocally reported as negative or positive for a deleterious mutation. Sensitivity, specificity, negative predictive value, positive predictive value, and areas under receiver operator characteristics (ROC) curves were calculated for each risk counselor and for BRCAPRO. All statistical tests were two sided. RESULTS: Using a greater-than-10% BRCA gene mutation probability threshold, the median sensitivity for identifying mutation carriers was 94% (range = 81% to 98%) for the eight risk counselors and 92% (range = 91% to 92%) for BRCAPRO. Median specificity at this threshold was 16% (range = 6% to 34%) for the risk counselors and 32% (range = 30% to 34%) for BRCAPRO (P =.04). Median area under the ROC curves was 0.671 for the risk counselors (range = 0.620 to 0.717) and 0.712 (range = 0.706 to 0.720) for BRCAPRO (P =.04). There was a slight, but not statistically significant, improvement in all counselor performance measures when BRCAPRO-assigned gene mutation probability information was included with the pedigrees. CONCLUSIONS: Sensitivity for identifying BRCA gene mutation carriers is similar for experienced risk counselors and the computer model BRCAPRO. Because the computer model consistently demonstrated superior specificity, overall discrimination between BRCA gene mutation carriers and BRCA gene mutation noncarriers was slightly better for BRCAPRO.

Breast Neoplasms↗
PubMedDate not supplied

Embracing computer modeling to address pandemic influenza in the 21st century.

Reacting to a pandemic influenza outbreak will require the mass distribution of vaccine, when available, which will require county health departments to set up and operate one or more mass vaccination clinics, also known as points of dispensing (PODs). Carefully planning these PODs before an event occurs is a difficult but important job. First, this article describes a tool--the Clinic Planning Model Generator computer program--designed to help public health agencies evaluate and make adjustments to their POD plans. The Clinic Planning Model Generator was built on data from a smallpox exercise and other biological agent POD exercises. Second, this article demonstrates the application of the Clinic Planning Model Generator through an example pandemic influenza scenario. This work is the result of an ongoing collaboration between Montgomery County, Maryland's Advanced Practice Center for Public Health Emergency Preparedness and Response, and the Institute for Systems Research at the University of Maryland.

Computer Simulation↗
PubMed2005

Possible uses of computer modeling of the functioning human hand.

This article includes a brief description of an approach to functional limb modeling including a summary of "helping hand," a computer model created by the authors. Potential uses of three-dimensional computer modeling of hand function are presented with some illustrations relevant to clinicians.

Computer Simulation↗
PubMed1994

Higher-order structure of bovine mitochondrial tRNA(SerUGA): chemical modification and computer modeling.

On the basis of enzymatic probing and phylogenetic comparison, we have previously proposed that mammalian mitochondrial tRNA(sSer) (anticodon UGA) possess a slightly altered cloverleaf structure in which only one nucleotide exists between the acceptor stem and D stem (usually two nucleotides) and the anticodon stem consists of six base pairs (usually five base pairs) [Yokogawa et al. (1991) Nucleic Acids Res. 19, 6101-6105]. To ascertain whether such tRNA(sSer) can be folded into a normal L-shaped tertiary structure, the higher-order structure of bovine mitochondrial tRNA(SerUGA) was examined by chemical probing using dimethylsulfate and diethylpyrocarbonate, and on the basis of the results a tertiary structure model was obtained by computer modeling. It was found that a one-base-pair elongation in the anticodon stem was compensated for by multiple-base deletions in the D and extra loop regions of the tRNA(SerUGA), which resulted in preservation of an L-shaped tertiary structure similar to that of conventional tRNAs. By summarizing the findings, the general structural requirements of mitochondrial tRNAs necessary for their functioning in the mitochondrial translation system are considered.

Alkylating Agents↗
PubMed2005

Linking environmental effects to health impacts: a computer modelling approach for air pollution.

UNLABELLED: STUDY OBJECTIVE AND SETTING: To develop a computer model, using a geographical information system (GIS), to quantify potential health effects of air pollution from a new energy from waste facility on the surrounding urban population. DESIGN: Health impacts were included where evidence of causality is sufficiently convincing. The evidence for no threshold means that annual average increases in concentration can be used to model changes in outcome. The study combined the "contours" of additional pollutant concentrations for the new source generated by a dispersion model with a population database within a GIS, which is set up to calculate the product of the concentration increase with numbers of people exposed within each enumeration district exposure response coefficients, and the background rates of mortality and hospital admissions for several causes. MAIN RESULTS: The magnitude of health effects might result from the increased PM10 exposure is small-about 0.03 deaths each year in a population of 3 500 000, with 0.04 extra hospital admissions for respiratory disease. Long term exposure might bring forward 1.8-7.8 deaths in 30 years. CONCLUSIONS: This computer model is a feasible approach to estimating impacts on human health from environmental effects but sensitivity analyses are recommended. RELEVANCE TO CLINICAL OR PROFESSIONAL PRACTICE: The availability of GIS and dispersion models on personal computers enables quantification of health effects resulting from the additional air pollution new industrial development might cause. This approach could also be used in environmental impact assessment. Care must be taken in presenting results to emphasise methodological limitations and uncertainties in the numbers.

Adolescent↗
PubMed2006

Influence of fiber optic probe geometry on the applicability of inverse models of tissue reflectance spectroscopy: computational models and experimental measurements.

Accurate recovery of tissue optical properties from in vivo spectral measurements is crucial for improving the clinical utility of optical spectroscopic techniques. The performance of inversion algorithms can be optimized for the specific fiber optic probe illumination-collection geometry. A diffusion-theory-based inversion method has been developed for the extraction of tissue optical properties from the shape of normalized tissue diffusion reflectance spectra, specifically tuned for a fiber probe that comprises seven hexagonally close-packed fibers. The central fiber of the probe goes to the spectrometer as the detecting fiber, and the surrounding six outer fibers are connected to the white-light source as illumination fibers. The accuracy of the diffusion-based inversion algorithm has been systematically assessed against Monte Carlo (MC) simulation as a function of probe geometry and tissue optical property combinations. By use of this algorithm, the spectral absorption and scattering coefficients of normal and cancerous tissue are efficiently retrieved. Although there are significant differences between the diffusion approximation and the MC simulation at short source-detector (SD) separations, we show that with our algorithm the tissue optical properties are well retrieved within the SD separation of 0.5-3 mm that is compatible with endoscopic specifications. The presented inversion method is computationally efficient for eventual real-time in vivo tissue diagnostics application.

Computer Simulation↗
PubMed2003

Computational model for forced expiration from asymmetric normal lungs.

We present a computational model to predict maximal expiration through a morphometry-based asymmetrical bronchial tree. A computational model with the Horsfield-like geometry of the airway structure, including wave-speed flow limitation and taking into consideration separate airflows from several independent alveolar compartments has been derived. The airflow values are calculated for quasistatic conditions by solving a system of nonlinear differential equations describing static pressure losses along the airway branches. Calculations done for succeeding lung volumes result in the semidynamic maximal expiratory flow-volume (MEFV) curve. Simulations performed show that the model captures the main phenomena observed in vivo during forced expiration: effort independence of the flow-volume curve for the most of vital capacity, independence of limited flow on the properties of airways downstream to the choke points, characteristic differences of lung regional pressures and volumes, and a shape of their variability during exhalation. Some new insights into the flow limitation mechanism were achieved. First, flow limitation begins at slightly different time instants in individual branches of the bronchial tree, however after a short period of time, all regional flows are limited in a parallel fashion. Hence, total flow at the mouth is limited for most of the expired lung volume. Second, each of the airway branches contribute their own flow-volume shape and just these individual flows constitute the measured MEFV curve. Third, central airway heterogeneity can play a crucial role in modification of the entire flow. Fourth, the bronchial tree asymmetry is responsible for a nongravitational component of regional volume variability. Finally, increased inhomogeneity yields results that cannot be explained nor re-created with the use of a symmetrical structure of the bronchial tree.

Air Pressure↗
PubMed1991

A computer model of auditory stream segregation.

A computer model is described which simulates some aspects of auditory stream segregation. The model emphasizes the explanatory power of simple physiological principles operating at a peripheral rather than a central level. The model consists of a multi-channel bandpass-filter bank with a "noisy" output and an attentional mechanism that responds selectively to the channel with the greatest activity. A "leaky integration" principle allows channel excitation to accumulate and dissipate over time. The model produces similar results to two experimental demonstrations of streaming phenomena, which are presented in detail. These results are discussed in terms of the "emergent properties" of a system governed by simple physiological principles. As such the model is contrasted with higher-level Gestalt explanations of the same phenomena while accepting that they may constitute complementary kinds of explanation.

Attention↗
PubMed1997

Computational models of visual neurons specialised in the detection of periodic and aperiodic oriented visual stimuli: bar and grating cells.

Computational models of periodic- and aperiodic-pattern selective cells, also called grating and bar cells, respectively, are proposed. Grating cells are found in areas V1 and V2 of the visual cortex of monkeys and respond strongly to bar gratings of a given orientation and periodicity but very weakly or not at all to single bars. This non-linear behaviour, which is quite different from the spatial frequency filtering behaviour exhibited by the other types of orientation-selective neurons such as the simple cells, is incorporated in the proposed computational model by using an AND-type non-linearity to combine the responses of simple cells with symmetric receptive field profiles and opposite polarities. The functional behaviour of bar cells, which are found in the same areas of the visual cortex as grating cells, is less well explored and documented in the literature. In general, these cells respond to single bars and their responses decrease when further bars are added to form a periodic pattern. These properties of bar cells are implemented in a computational model in which the responses of bar cells are computed as thresholded differences of the responses of corresponding complex (or simple) cells and grating cells. Bar and grating cells seem to play complementary roles in resolving the ambiguity with which the responses of simple and complex cells represent oriented visual stimuli, in that bar cells are selective only for form information as present in contours and grating cells only respond to oriented texture information. The proposed model is capable of explaining the results of neurophysiological experiments as well as the psychophysical observation that the perception of texture and the perception of form are complementary processes.

Animals↗
PubMed2005

An effective simulation of aqueous micellar aggregates by computational models.

We have computationally studied the interaction modes, localization and orientation of a benzene (Bz) molecule on the surface of micelles formed by cetyltrimethylammonium salts CTAX. Experimental 1H-NMR data on complexation shifts induced by Bz on the polar head hydrogens and on the adjacent methylene hydrogens of CTAX have been interpreted using a computational approach that combines an automatic molecular docking procedure with a calculation module that accounts for NMR complexation shifts due to ring current diamagnetic anisotropy. Three different models were used to reduce the complexity of the micellar system. Computational results, in good agreement with available experimental data, point to a preferential localization of the Bz molecule along the CTAX alkyl tail, about 3.9 angstroms away from the charged nitrogen. The Bz molecular plane is predicted perpendicular to the C-H bonds of the alkyl tail. The good results obtained with the simplest model suggest that it could be used to study more complex systems involving surfactants endowed with molecular recognition or catalytic abilities.

Catalysis↗
PubMed2003

Automated detection of focal cortical dysplasia lesions using computational models of their MRI characteristics and texture analysis.

Focal cortical dysplasia (FCD), a malformation of cortical development, is a frequent cause of pharmacologically intractable epilepsy. FCD is characterized on Tl-weighted MRI by cortical thickening, blurring of the gray-matter/white-matter interface, and gray-level hyperintensity. We have previously used computational models of these characteristics to enhance visual lesion detection. In the present study we seek to improve our methods by combining these models with features derived from texture analysis of MRI, which allows measurement of image properties not readily accessible by visual analysis. These computational models and texture features were used to develop a two-stage Bayesian classifier to perform automated FCD lesion detection. Eighteen patients with histologically confirmed FCD and 14 normal controls were studied. On the MRI volumes of the 18 patients, 20 FCD lesions were manually labeled by an expert observer. Three-dimensional maps of the computational models and texture features were constructed for all subjects. A Bayesian classifier was trained on the computational models to classify voxels as cerebrospinal fluid, gray-matter, white-matter, transitional, or lesional. Voxels classified as lesional were subsequently reclassified based on the texture features. This process produced a 3D lesion map, which was compared to the manual lesion labels. The automated classifier identified 17/20 manually labeled lesions. No lesions were identified in controls. Thus, combining models of the T1-weighted MRI characteristics of FCD with texture analysis enabled successful construction of a classifier. This computer-based, automated method may be useful in the presurgical evaluation of patients with severe epilepsy related to FCD.

Adult↗
PubMed2004

Editorial: computational modelling of cell & tissue processes & function.

Computational modelling of whole biological systems from cells to organs is gaining momentum in cell biology and disease studies. This pathway is essential for the derivation of explanatory frameworks that will facilitate the development of a predictive capacity for estimating outcomes or risk associated with particular disease processes and therapeutic or stressful treatments. This article introduces a series of invited papers covering a hierarchy of issues and modelling problems, ranging from crucial conceptual considerations of the validity of cellular modelling through to multi-scale modelling up to organ level. The challenges and approaches in cellular modelling are described, including the potential of 'in silico ' modelling applications for receptor-ligand interactions in cell signalling, simulated organ dysfunction (i.e., heart), human and environmental toxicity and the progress of the IUPS Physiome Project. A major challenge now facing biologists is how to translate the wealth of reductionist detail about cells and tissues into a real understanding of how these systems function and are perturbed in disease processes. In biomedicine, simulation models of biological systems now contain sufficient detail, not only to reconstruct normal functions, but also, to reconstruct major disease states. More widely, simulation modelling will aid the targeting of current 'knowledge gaps' and how to fill them; and also provide a research tool for selecting critical factors from multiple simulated experiments for real experimental design. The envisaged longer-term end- product is the creation of simulation models for predicting drug interactions and harmful side-effects; and their use in therapeutic and environmental health risk management. Finally, we take a speculative look at possible future scenarios in cellular modelling, where it is envisioned that integrative biology will move from being largely qualitative and instead become a highly quantitative, computer-intensive discipline.

Cell Physiological Phenomena↗
PubMed1976

Subsite mapping of enzymes. Depolymerase computer modelling.

We have developed a depolymerase computer model that uses a minimization routine. The model is designed so that, given experimental bond-cleavage frequencies for oligomeric substrates and experimental Michaelis parameters as a function of substrate chain length, the optimum subsite map is generated. The minimized sum of the weighted-squared residuals of the experimental and calculated data is used as a criterion of the goodness-of-fit for the optimized subsite map. The application of the minimization procedure to subsite mapping is explored through the use of simulated data. A procedure is developed whereby the minimization model can be used to determine the number of subsites in the enzymic binding region and to locate the position of the catalytic amino acids among these subsites. The degree of propagation of experimental variance into the subsite-binding energies is estimated. The question of whether hydrolytic rate coefficients are constant or a function of the number of filled subsites is examined.

Amino Acid Sequence↗
PubMedDate not supplied

Computer modeling of interactions of an electric motor, circulatory system, and rotary blood pump.

The innovative ventricular assist systems (IVAS) is the next generation ventricular assist device for use as a permanent implantable device. Its practical application depends upon control of the electric motor and interactions of the electric motor, blood pump, and circulatory system. Computer modeling and simulation are necessary to investigate and evaluate the interactions and feasibility of sophisticated control algorithms. In this paper, a computer model of the complete system, including the cardiovascular system, blood pump, and electric motor, is proposed. The model is obtained based on an electric circuit model of the cardiovascular system, a parametric model of the blood pump, and a dynamic model of the electric motor. The cardiovascular system uses nonlinear parameters to simulate the time-varying property of the ventricles, and the cannula collapse effect caused by over-pumping. The blood pump model can be obtained either from pump design data, or test data. The motor control can be operated with closed-loop regulation, depending upon physiologic requirements. Different operation modes (current or speed) of the electric motor can be simulated. The computer model is implemented using MATLAB. Various motor operation modes are simulated and their effects are evaluated. By adjusting the motor input, the pump can achieve proper output so that normal physiology can be obtained. In addition to evaluating existing operation modes and their effect on the physiologic system, the computer simulation results show that this computer model can contribute significantly to the development of new physiologic control algorithms. It is demonstrated that, using this motor-pump-physiology interaction model, development of an innovative ventricular assist system can be greatly facilitated.

Computer Simulation↗
PubMed1992

A computer model of the kidney.

We developed a computer model of renal function that factors perfusion pressure, serum sodium, potassium, antidiuretic hormone and aldosterone concentrations to derive urine output, urinary sodium and urinary potassium excretion. The model implements Uttamsingh's (Uttamsingh, R.J., et al. Mathematical model of the human renal system. Med. Biol. Eng. Comput. 23 (1985) 525-536) analytical equations as an electrical circuit suitable for network analysis. This model is useful for studying the effects of renal blood flow and the humoral milieu on renal function in normal kidneys either as a stand-alone unit or in combination with other physiological electrical models.

Computer Simulation↗
PubMed2001

Evaluating auditory performance limits: i. one-parameter discrimination using a computational model for the auditory nerve.

A method for calculating psychophysical performance limits based on stochastic neural responses is introduced and compared to previous analytical methods for evaluating auditory discrimination of tone frequency and level. The method uses signal detection theory and a computational model for a population of auditory nerve (AN) fiber responses. The use of computational models allows predictions to be made over a wider parameter range and with more complete descriptions of AN responses than in analytical models. Performance based on AN discharge times (all-information) is compared to performance based only on discharge counts (rate-place). After the method is verified over the range of parameters for which previous analytical models are applicable, the parameter space is then extended. For example, a computational model of AN activity that extends to high frequencies is used to explore the common belief that rate-place information is responsible for frequency encoding at high frequencies due to the rolloff in AN phase locking above 2 kHz. This rolloff is thought to eliminate temporal information at high frequencies. Contrary to this belief, results of this analysis show that rate-place predictions for frequency discrimination are inconsistent with human performance in the dependence on frequency for high frequencies and that there is significant temporal information in the AN up to at least 10 kHz. In fact, the all-information predictions match the functional dependence of human performance on frequency, although optimal performance is much better than human performance. The use of computational AN models in this study provides new constraints on hypotheses of neural encoding of frequency in the auditory system; however, the method is limited to simple tasks with deterministic stimuli. A companion article in this issue ("Evaluating Auditory Performance Limits: II") describes an extension of this approach to more complex tasks that include random variation of one parameter, for example, random-level variation, which is often used in psychophysics to test neural encoding hypotheses.

Animals↗