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Results for “computational modelling”

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PubMed1984

Sensitivity and specificity of the computational model for maximal expiratory flow.

The computational model for forced expiratory flow from human lungs of Lambert and associates (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 44-56, 1982) was used to investigate the sensitivity of maximal expiratory flow to lung properties. It was found that maximal flow is very sensitive to recoil pressure and airway areas but not very sensitive to lung volume, airway compliance, and airway length. Linear programming was used to show that a given air flow-pressure curves was compatible with a fairly wide range of airway properties. Additional data for maximal flow with a He-O2 mixture narrowed the range somewhat. It was shown that the flow-pressure curve contains more information about central than peripheral airways and that information about the latter is obtainable only from flows at recoils less than 2 cmH2O. Parameter ranges compatible with individual flow-pressure curves showed differences that demonstrated that such curves give some indication of individual central airway properties.

Airway Resistance↗

PubMed1977

A Monte Carlo computer model to investigate patient scheduling.

A Monte Carlo computer model was developed to investigate various types of patient appointment schedules for a single channel queue. Input parameters included the incidence of no-shows, the rate of unscheduled walk-ins, the frequency distribution of physician examination times, and the string of appointment times. The results included the frequency distributions of physician utilization rates and the total waiting time of all patients. Five hospital clinics were simulated. Even increment schedules yielded the best trade-off between physician utilization and patient waiting.

Appointments and Schedules↗

PubMed1989

Computer model of cardiac repolarization processes and of the recovery sequence.

A computer model simulating both excitation and recovery processes within a block of heart muscle tissue has been developed and implemented on different IBM PC AT compatible computers. The model incorporates blocks of tissue consisting of several thousand elements and introduces phenomena which are completely or partly omitted in other existing cardiac electrophysiology models. These phenomena include the electric anisotropy of the tissue, different durations of repolarization in different layers of tissue, and the different shapes of action potential which correspond to cells excited when not fully recovered. Implementation of the model on small personal computers requires the use of a special data structure management and an effective algorithmic background. The program of the model is written in PASCAL and uses dynamically allocated data structures and the asynchronous simulation technique of event planing. These techniques are described in detail. The model has been used in various experiments. Results of simulation studies are presented in the form of modeled three-lead electrocardiographic records. The experimental series which are described include basic patterns of regular activation sequences, modeling of premature beats, simulation of effects due to fast pacing, models of ischemia and infarction, simulation of reentry mechanisms with a special reference to the initiation of ventricular fibrillation, and models of late potentials. The future development of more realistic models of the cardiac recovery process is also discussed.

Action Potentials↗

PubMedDate not supplied

[Computer modeling of mechanisms of the information processing in the olfactory bulb. I. Model of the structure-functional organizations of neuronal elements in the olfactory bulb and receptor epithelium].

A computer model of the olfactory bulb was constructed. The paper describes: 1) the general architecture of a model neuron network that reflects the neurophysiological experimental and theoretical data on the structural and functional organization of the peripheral part of the olfactory system, the olfactory bulb with inputs from olfactory receptor neurons; 2) the organization of each of three levels of the model: receptors, olfactory glomeruli, and basic neurons; and 3) a scenario of the computer model work. In some aspects, in particular, in the principle of information presentation, the treatment of the role of basic neurons (mitral and tufted cells), and their interrelations in modules, the model favorably differs from the available olfactory bulb models. The model is basic and provides further refinement of the architecture, an increase in the number of modules, and the modeling of the learning process.

Animals↗

PubMed1987

A computer model of hemorrhagic shock in domestic swine.

We used a modified version of the computer model of the circulation developed by C.V. Greenway (Pharmacol Rev 33:213-251, 1982) to study the volume-pressure relationship of the systemic venous circulation during and immediately after massive blood loss. Our theoretical predictions were based on experimental measurements performed in conscious, chronically instrumented swine subjected to massive and rapid loss of a predetermined amount of blood. These animals were subjected to an exponential removal of either 50% of their calculated blood volume in 1 hour or a linear removal of 60% in 15 minutes. Our computer model indicates a hysteresis effect between the volume-pressure curves during and immediately following hemorrhage. The results emphasize the importance of venous capacitance changes as a compensatory response to blood loss.

Animals↗

PubMed1996

Sensory gating in a computer model of the CA3 neural network of the hippocampus.

We have developed a unique computer model of the CA3 region of the hippocampus that simulates the P50 auditory evoked potential response to repeated stimuli in order to study the neuronal circuits involved in a sensory processing deficit associated with schizophrenia. Our computer model of the CA3 hippocampal network includes recurrent activation from within the CA3 region as well as input from the entorhinal cortex and the medial septal nucleus. We used the model to help us determine if the cortical and septal inputs to the CA3 hippocampus alone are responsible for the gating of auditory evoked activity, or if the strong recurrent activity within the CA3 region contributes to this phenomenon. The model suggests that the medial septal input is critical for normal gating; however, to a large extent the activity of the medial septal input can be replaced by simulated stimulation of the hippocampal neurons by a nicotinic agonist. The model is thus consistent with experimental data that show that nicotine restores gating of the N40 evoked potential in fimbria-fornix lesioned rats and of the P50 evoked potential in schizophrenic patients.

Animals↗

PubMed1985

Shell computer model of cardiac electropotential changes.

A discrete process computer model has been developed to simulate the electropotential changes of heart musculature and the operation of the cardiac conduction system. The model is implemented on an ICL-4/72 computer and is oriented to cardiac rhythm studies, allowing practically all rhythm pathologies, including pacemaker applications, to be simulated. The paper describes in detail the principles on which the model is based, compares the model with other models of the same system and shows concisely some results of simulation experiments in the form of computer generated ECG records.

Atrioventricular Node↗

PubMed1986

Computer modeling of actinomycin D interactions with double-helical DNA.

We have performed molecular mechanical calculations on intercalation complexes of actinomycin D with a series of base-paired hexanucleoside pentaphosphates; d(GCGCGC)2, d(GCCGGC)2, d(GCATGC)2, d(GCTAGC)2 and d(ATGCAT)2. Our results are in good agreement with previous experimental work on sequence selectivity. The results provide a rationalization for the strong preference of actinomycin D to intercalate on the 3' side of guanine residues, consistent with previously proposed models. Finally, the computed structures for d(ATGCAT)2-actinomycin D complexes have been compared with two-dimensional nuclear magnetic resonance nuclear Overhauser effect experimental results. To our knowledge, this is the first extensive comparison of molecular mechanical model structures for a drug-DNA complex with experimental solution phase data. We find generally good agreement between our computational models and the experimental solution phase structures.

Computers↗

PubMed1995

Validation of a computer model of haemorrhage and transcapillary refill.

A computer model is described which uses blood volume deficit and its duration to simulate the first two hours of haemorrhage, including an estimation of the blood volume added by Starlings transcapillary refill mechanism. Computer prediction of the haematocrit was compared with published data on haemorrhage in animals. There was close correlation with data on the haemodilution caused by Starling's transcapillary refill mechanism in conscious swine (r = 0.84).

Animals↗

PubMed1989

Three-dimensional computer model of the heart: fibrillation induced by extrastimulation.

We present a three-dimensional (3D) computer model that simulates electrical activity in the heart during fibrillation. A real dog heart is discretized to form 1473 interconnected cubic elements. The model exhibits normal activation and recovery from pacing. Five or more extrastimuli induce a self-sustaining tachyarrhythmia that soon degenerates into a fibrillatory rhythm. The extrastimuli increase the excitability of the myocardial cell population. The result is a rapid re-excitation of cells that allows for only a partial recovery of cell action potential. This suggests that a dispersion of refractory states of the cell population is the cause of fibrillation in this computer model.

Animals↗

PubMed1991

An evaluation of eight computer models of mammalian inner hair-cell function.

Eight computer models of auditory inner hair cells have been evaluated. From an extensive literature on mammalian species, a subset of well-reported auditory-nerve properties in response to tone-burst stimuli were selected and tested for in the models. This subset included tests for: (a) rate-level functions for onset and steady-state responses; (b) two-component adaptation; (c) recovery of spontaneous activity; (d) physiological forward masking; (e) additivity; and (f) frequency-limited phase locking. As models of hair-cell functioning are increasingly used as the front end of speech-recognition devices, the computational efficiency of each model was also considered. The evaluation shows that no single model completely replicates the subset of tests. Reasons are given for our favoring the Meddis model [R. Meddis, J. Acoust. Soc. Am. 83, 1056-1063 (1988)] both in terms of its good agreement with physiological data and its computational efficiency. It is concluded that this model is well suited to provide the primary input to speech recognition devices and models of central auditory processing.

Animals↗

PubMed2001

Computational models of cells and tissues: machines, agents and fungal infection.

Computational models have been of interest in biology for many years and have represented a particular approach to trying to understand biological processes and phenomena from a systems point of view. Much of the early work was rather abstract and high level and probably seemed to many to be of more philosophical than practical value. There have, however, been some advances in the development of more realistic models and the current state of computer science research provides us with new opportunities through both the emergence of models that can model seriously complex systems and also the support that modern software can give to the modelling process. This paper describes a few of the early simple models and then goes on to look at some new ideas in the area with a particular application drawn from the world of mycology. Some general principles relating to how new and emerging computational techniques can help to represent and understand extremely complex models conclude the paper.

Computational Biology↗

PubMed1995

Computer models: killing mosquitoes with information.

This paper looks at the relationship between man and mosquitoes from the perspective of coevolution. From this perspective, the primacy of information processing in vector control programs becomes acutely evident. A composite mosquito control program is developed and illustrated to show the benefits derived from incremental increases in information. The use of computer modeling is seen as the next logical step to be taken by vector control personnel to add the next increment of efficiency and effectiveness. This step could well lead to significant reductions or perhaps the elimination of the need for pesticide use. The author encourages the use of computer modeling in teams as the means to learn across disciplines. The feasibility of this approach has been greatly enhanced by the availability of off-the-shelf modeling programs. The author appeals to university and vector control professionals to support students and staff in learning computer modeling techniques.

Animals↗

PubMed2000

Computational modeling of the baroreflex arc: nucleus tractus solitarius.

In this study, we examine the utility of computational modeling in understanding nervous system function. We start by examining the reasons for, and major approaches to, computational modeling. We then chose a modeling approach and applied different variations to understanding nucleus tractus solitarius (NTS) neuronal responses to various baroreceptive stimuli. We examine the results in light of our objectives and with regard to the known parameters of the system under investigation. Our results demonstrate that modeling can be a useful tool in analysis of (and examination of underlying mechanisms for) NTS behavior on many levels.

Animals↗

PubMed1999

A computational model for visual selection.

We propose a computational model for detecting and localizing instances from an object class in static gray-level images. We divide detection into visual selection and final classification, concentrating on the former: drastically reducing the number of candidate regions that require further, usually more intensive, processing, but with a minimum of computation and missed detections. Bottom-up processing is based on local groupings of edge fragments constrained by loose geometrical relationships. They have no a priori semantic or geometric interpretation. The role of training is to select special groupings that are moderately likely at certain places on the object but rate in the background. We show that the statistics in both populations are stable. The candidate regions are those that contain global arrangements of several local groupings. Whereas our model was not conceived to explain brain functions, it does cohere with evidence about the functions of neurons in V1 and V2, such as responses to coarse or incomplete patterns (e.g., illusory contours) and to scale and translation invariance in IT. Finally, the algorithm is applied to face and symbol detection.

Algorithms↗

PubMed1987

A computational model of reasoning from the clinical literature.

This paper explores the premise that a formalized representation of empirical studies can play a central role in computer-based decision support. The specific motivations underlying this research include the following propositions: Reasoning from experimental evidence contained in the clinical literature is central to the decisions physicians make in patient care. A computational model, based upon a declarative representation for published reports of clinical studies, can drive a computer program that selectively tailors knowledge of the clinical literature as it is applied to a particular case. The development of such a computational model is an important first step toward filling a void in computer-based decision support systems. Furthermore, the model may help us better understand the general principles of reasoning from experimental evidence both in medicine and other domains. Roundsman is a developmental computer system which draws upon structured representations of the clinical literature in order to critique plans for the management of primary breast cancer. Roundsman is able to produce patient-specific analyses of breast cancer management options based on the 24 clinical studies currently encoded in its knowledge base. The Roundsman system is a first step in exploring how the computer can help to bring a critical analysis of the relevant literature to the physician, structured around a particular patient and treatment decision.

Artificial Intelligence↗

PubMed1999

[Study of the posterior cruciate ligament using a 3D computer model: ligament biometry during flexion, application to surgical replacement of the ligament].

We have developed a 3D computed model of the knee joint, constructed from MRI acquisitions in a living individual. We have used this model to perform an anatomic and biometric study of the posterior cruciate ligament (PCL) during flexion, and an assessment of the optimal location for an intraarticular graft. The method used a 3D computed model constructed from MRI acquisitions during knee flexion (0 to 75 degrees). The range of motion was limited by a positioning device. We took 13 acquisitions from 0 to 75 degrees of flexion. Each acquisition consisted of 21 sagittal cross sections of 3 mm slice thickness. We used the Delaunay reconstruction to obtain a 3D geometric model. A matching process to fix one part of the articulation during the movement, allows for the kinematic analysis of the tibia relative to the fixed femur. This model allows to follow the displacement of a bone point during knee flexion. Knowing the relative displacement of the bone insertions of the ligament, it may be possible to determine the length of the PCL and its bands, to evaluate the length variation during movement, and to determine the optimal location for the insertion of an intraarticular graft, that would lead to the least stretch during flexion. It was found that the mean length of the PCL was 30.2 mm, with the posterior band being 30% longer than the anterior band. During flexion the posterior band increases its length by 10% at 50 degrees flexion, and by 20% at 75 degrees flexion. The anterior band stretches more, to reach 40% elongation at 75 degrees flexion. The best position for insertion of a graft seems to be in the posterolateral portion of the anatomic tibial insertion, and posterior to the anatomic femoral insertion. This method confirms the data in the literature, states precisely the length of the different bands of the PCL, and specifies the points of insertion for a graft, which lead to the least variation in length during flexion.

Biometry↗

PubMed1998

Using computer modeling to help identify patient subgroups in clinical data repositories.

OBJECTIVE: The ability to accurately and efficiently identify patient cases of interest in a hospital information system has many important clinical, research, educational and administrative uses. The identification of cases of interest sometimes can be difficult. This paper describes a two-stage method for searching for cases of interest. DESIGN: First, a Boolean search is performed using coded database variables. The user classifies the retrieved cases as being of interest or not. Second, based on the user-classified cases, a computer model of the patient cases of interest is constructed. The model is then used to help locate additional cases. These cases provide an augmented training set for constructing a new computer model of the cases of interest. This cycle of modeling and user classification continues until halted by the user. MEASUREMENTS: This paper describes a pilot study in which this method is used to identify the records of patients who have venous thrombosis. RESULTS: The results indicate that computer modeling enhances the identification of patient cases of interest.

Bayes Theorem↗