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PubMed2006

An integrated coronary circulation teaching model.

OBJECTIVES: We present in this paper a model of the coronary circulation. This model is integrated with a model of the systemic circulation, and contains models for oxygen supply and demand. METHODS: Three compartments are created: one for the right ventricle, one for the epicardial segment of the left ventricle and one for the endo-cardial segment of the left ventricle. The model was implemented in the Java programming language and contains a visual representation of the left and right ventricles which beat in real time. Color shading is used to represent the partial pressure of oxygen in the segments. A multitude of model parameters can be changed to simulate different scenarios. RESULTS: The output of the model was characterized under different conditions and the results verified by clinicians. CONCLUSIONS: Educational models of human physiology can be very useful for a more in depth understanding of complete physiologic systems. The models must however have enough complexity, interaction with other systems, and realism to show the concepts being taught.

Blood Flow Velocity↗

PubMed1992

Projective invariance and the kinetic depth effect.

Seven experiments test the assumption that, in the kinetic depth effect, observers have reliable and direct access to the equivalence of shapes in projective geometry. The assumption is implicit in 'inverse optics' approaches to visual form perception. Observers adjusted a comparison shape to match a standard shape; both standard and comparison were portrayed as in continuous rotation in space, using a graphics computer. The shapes were either plane quadrilaterals or solid prisms. The angular difference of the planes of the shapes was varied, as was the dot density of a texture in those planes. Departure from projective equivalence was measured in six studies by measuring the planar analogue of cross ratio, and in a seventh by measuring the cross ratio for points in space. Projective equivalence was not found to be perceived uniformly, except in one experiment that did not involve rotation in depth. Otherwise changes in orientation of up to 180 degrees about a single coordinate axis had no significant effect on matches in shape, while changes in orientation about more than one coordinate axis produced significant effects. The addition of texture and a change in rotation speed did not correct departures from projective equivalence.

Adult↗

PubMed1991

Apparatus for gel electrophoresis with continuous monitoring of individual DNA molecules by video epifluorescence microscopy.

Apparatus for gel electrophoresis with continuous scanning by video epifluorescence microscopy was constructed and applied to measurements on individual DNA molecules in the size range of several hundred kilobase pairs. The gel electrophoresis apparatus comprises a horizontal glass cell and several commercially available components--an epifluorescence microscope, an image intensifier, two video cameras, a monitor, videotape recorder and voltmeter. Data in the form of videotapes can be subsequently analyzed on a computer graphics work station.

DNA↗

PubMed1980

Design of mirror systems for commercial vehicles.

This paper describes a computer aided design project for the evaluation of alternative mirror systems for a range of commercial vehicles. Computer modelling of mirror systems introduces the ergonomics parameters into the design programme at an early stage. The flexibility of computer modelling allows a far greater range of designs to be evaluated. The problems can be studied and resolved before producing a series of mirror designs to be evaluated by more conventional techniques on prototype vehicles. Mirrors designed in this way are less likely to require major redesign. Compliance with the legislative requirements of mirror design was a major consideration. Attempts were also made to optimise mirror systems for a range of cabs basing the evaluations on ergonomic as well as legislative criteria. Additionally, consideration was given to the use of mirrors for viewing trailer swing, passenger exit surveillance (for public service vehicles) and the viewing of objects close to high cabs. SAMMIE (System for Aiding Man-Machine Interaction Evaluation), a computer-aided workplace and work task design system, was used to model the vehicles and to produce the required mirror views on a computer graphics terminal.

Journal Article↗

PubMed1988

Modification of trypsin-solubilized cytochrome b5, apocytochrome b5, and liposome-bound cytochrome b5 by diethylpyrocarbonate.

The interactions of diethylpyrocarbonate (DEP) with the various forms of cytochrome b5 were studied to gain a better understanding of the factors that influence the extent of modification of the axial histidines of cytochrome b5. Very low concentrations of DEP were able to decrease the heme binding capacity of apocytochrome b5. Moreover, it was shown that two additional histidines, presumed to be the axial ligands (His 39 and 63), were modified in the apo but not the holo form of a given preparation of cytochrome b5. Trypsin-solubilized bovine cytochrome b5 was resistant to the effects of DEP. A 200-fold molar excess of DEP displaced only 15% of the heme in the trypsin-solubilized protein in contrast to an 84% displacement of the heme in the detergent-solubilized protein. However, detergent-solubilized cytochrome b5 which had been incorporated into phospholipid vesicles exhibited the same reactivity with DEP as did the trypsin-solubilized protein. This is attributed to the fact that the two resistant preparations of cytochrome b5 are monomeric in their respective environments while detergent-solubilized cytochrome b5 is known to exist as an octamer in aqueous solutions. Our studies suggest that dissociation of the octamer to the monomer results in a conformational change that decreases the reactivity of the axial ligands of the hydrophilic heme-containing domain of cytochrome b5. Examination of the cytochrome b5 molecule by computer graphics indicates that a tunnel leads from the surface of the molecule to axial histidine 63 and that axial histidine 39 is buried.

Animals↗

PubMed1990

Mode of assembly of amphipathic helical segments in model high-density lipoproteins.

The structure of discoidal apo A-I-phospholipid complexes, representing the metabolic precursors of mature high-density lipoprotein particles, was studied by a combination of both a theoretical and an experimental approach. The secondary structure of the complex was determined by circular dichroic measurements, while the relative orientation of the apo A-I helical segments and of the phospholipid acyl chains was determined by ATR infrared measurements. Fluorescence energy transfer between the tryptophan residues of apo A-I and fluorescent phospholipid probes yielded an estimation of the relative topography of the lipid and apolipoprotein components in discoidal and spherical particles. The theoretical approach consisted of the identification of the helical segments in various apo A-I species. These segments were then oriented at a lipid/water interface by minimization of their hydrophobic and hydrophilic transfer energies. The calculation of the hydrophobicity profiles along the axis of the helices leads to the identification of specific interactions between pairs of helices. The helices were further assembled together with the phospholipids by computer modelling, enabling an estimation of the dimensions of the complex. The combination of the experimental and theoretical results yielded a model for discoidal apolipoprotein-phospholipid complexes, in which the amphipathic helical segments are oriented along the edges of the discs. Such a model can be extended to the conversion of these complexes into mature spherical HDL, through the formation of a cholesteryl ester core.

Amino Acid Sequence↗

PubMed1984

Molecular models for the interaction of the anti-tumour drug nogalamycin with DNA.

Computer graphics and non-bonded energy calculations have been used to model the intercalative binding of the anti-tumour antibiotic nogalamycin, to double-stranded DNA. The drug is predicted to bind preferentially to A-T rich sites. Specific hydrogen bonds to the exocyclic amino group of adenine bases on the 3' side of an intercalative site have been found by the modelling procedure.

DNA↗

PubMed1985

Dissociation kinetics of DNA-anthracycline and DNA-anthraquinone complexes determined by stopped-flow spectrophotometry.

The first order rate constants for the dissociation of daunorubicin, doxorubicin, and 1-; 1,4-; 1,5-; and 1,8-; N,N-diethylaminoethylamino-substituted anthraquinones from calf thymus DNA were determined using stopped-flow spectrophotometry. Sodium dodecyl sulphate was used to disrupt the equilibrium. In all cases there was an increase in the rate constant with temperature. The dissociation rate constants at 20 degrees, 25 degrees and 37 degrees, were in the order 1-; much greater than 1,8-; greater than 1,4-; greater than daunorubicin and doxorubicin greater than 1,5-disubstituted anthraquinone. The 1,5-disubstituted anthraquinone (VII) thus shows the slowest rate of dissociation from DNA; the DNA complex dissociating more slowly than the DNA complexes of the anthracyclines, daunorubicin and doxorubicin. The result is consistent with the data from computer graphics modelling studies [39] which show that DNA-breathing (transient base pair unstacking) has to occur to allow the docking of the 1,5-disubstituted anthraquinone (VII) into the receptor site. Hence once the 1,5-disubstituted anthraquinone molecule has intercalated into DNA, DNA-breathing is required before dissociation can take place. This is not necessary with the other compounds (though the 1,4-disubstituted anthraquinone (V) can bind in this manner as well). So the very slow dissociation of the DNA/1,5-disubstituted anthraquinone complex relative to that of the DNA complexes of the other compounds examined here, supports the proposed mode of binding [39].

Anthraquinones↗

PubMed1987

Competition of milrinone, a non-iodinated cardiac inotropic agent, with thyroid hormone for binding sites on human serum prealbumin (TBPA).

Milrinone [2-methyl-5-cyano-(3,4'-bipyridin)-6(1H)-one] is a positive cardiac inotropic agent recently shown to have thyromimetic activity in vitro in a rabbit myocardial membrane Ca2+-ATPase system [K. M. Mylotte et al., Proc. natn. Acad. Sci. U.S.A. 82, 7974 (1985)]. In the present studies, milrinone was examined for activity as an inhibitor of iodothyronine binding by human serum thyroid hormone transport proteins, thyroxine-binding globulin (TBG), prealbumin (TBPA) and albumin. Polyacrylamide gel electrophoresis at pH 9.0 of sera equilibrated with [125I]thyroxine showed that milrinone competed with L-thyroxine (T4) for binding sites on TBPA (10 and 100 microM milrinone caused 61 and 73% reductions, respectively, in T4 binding to TBPA, P less than 0.01); T4 displaced from TBPA was bound by TBG and albumin. Comparable reductions in T4 binding to TBPA were observed in electrophoretic studies conducted at pH 7.4. Binding of triiodo-L-thyronine (T3) to TBPA was electrophoretically confirmed and shown to be decreased in the presence of milrinone. Electrophoresis of purified TBPA also demonstrated that [14C]milrinone co-migrated with this transport protein and that milrinone displaced tracer T4 from TBPA. Amrinone, the 2-H-5-NH2 analog of milrinone, had less than 5% of the activity of milrinone as an inhibitor of T4 binding in electrophoretic studies. Scatchard analysis of T4 and milrinone binding to purified TBPA, measured by equilibrium dialysis, showed two classes of binding sites, with association constants, respectively, of 6.1 X 10(7) M-1 and 1.6 X 10(6) M-1 for T4, and 1.7 X 10(6) M-1 and 8.9 X 10(2) M-1 for milrinone. Computer graphic modeling of the binding of milrinone to the T4 site in the crystal structure of TBPA showed that milrinone best occupied this site when the substituted bipyridine ring overlapped the phenolic ring of T4. In this orientation the 5-cyano group, which has an electronegativity similar to that of iodine, occupied the same volume as the 5'-iodine of T4. The 5-amino group of amrinone lacks these characteristics. In this orientation, the keto function of milrinone overlapped the T4 4'-hydroxyl and could participate in similar intermolecular interactions. Thus, milrinone, a non-iodinated bipyridine, and thyroid hormone share structural and biochemical homologies and compete for the same binding site on TBPA.

Amrinone↗

PubMed1977

Morphanalysis of craniofacial dysharmony.

The first stage in the morphanalysis of craniofacial dysharmony involves induction. In this process, individual analytic morphograms are combined to form analytic histograms, which in turn are connected to form analytic histomorphograms, which provide three-dimensional statements about the variation in craniofacial structures in a population. The second stage involves deduction, in which the analytic morphograms of a particular patient are compared with appropriate analytic histomorphograms, so that a diagnosis of the three-dimensional nature of the dysharmony can be made. Craniofacial morphanalysis is performed manually in small scale enquiries but the methods have been converted to computer-graphic technology for large-scale studies. A clinical morphanalysis service is currently conducted and a standard reference atlas is being prepared.

Adolescent↗

PubMed1983

A graphic computerized system for reporting and analysis of coronary angiograms.

A graphic computer based system for coronary angiographic reporting and data storage has been developed. It uses a multisegmental model of the coronary tree so that precise localization of coronary lesions can be made in relation to major branches. The percentage narrowing of the vessel, the length of the lesion, and diameter of the distal coronary vessel can be measured. Collateral vessels, coronary artery bypass grafts, and coronary artery spasm are recorded. The system is simple to use and useful for routine clinical reporting and for detailed analysis of coronary lesions.

Angiography↗

PubMed1986

Three-dimensional reconstruction from serial sections. IV. The reassembly problem.

In many fields of biology and medicine there is a pressing need for quantitative descriptions of biological structures at a resolution of micrometers. This need is currently met best by three-dimensional reconstruction from serial sections. The preliminary steps in three-dimensional reconstruction include fixation, embedding in plastic, introduction of fiducials, serial sectioning, and staining. At the light microscope level, with which we are chiefly concerned, one will usually want to do photomicrography (or videomicrography) of adjacent fields within individual tissue sections. The resultant images are projected onto a digitizer pad and the contours of interest manually digitized. From the digitized coordinates generated thereby, one wishes to generate a likeness of the original object, using computer graphic displays, and to then do interactive morphometrics. The problem of combining the digitized coordinates so as to produce a numerically faithful representation of the original object (i.e., the reassembly problem) is, as a practical matter, nontrivial. A technical description of the reassembly problem is presented. The main factors entering into a solution of the problem are discussed and a mathematical statement of the solution is given.

Anatomy↗

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↗

PubMed1989

Expected pressure-volume heterogeneity within the lung.

Using a model of the lung providing for pressure-volume (P-V) heterogeneity, we reproduced straight (allowing for some concavity or convexity) alveolar plateaus in the nitrogen washout curve with a slope identical to an experimentally measured one (1.2% N2/liter). In a two-unit lung, with one unit of high volume (H) at total lung capacity (TLC) and another of low volume (L) at TLC, three variables could be adjusted to produce the desired alveolar plateaus: the ratio of TLCL/TLCH; the ratio of functional residual capacity, FRCL/FRCH; and the ratio of the steepness constants of their sigmoid P-V curve, KL/KH. We searched for all possible combinations of the three variables that yielded the desired alveolar plateau. For any TLCL/TLCH ratio, there were two single-value solutions for the FRCL/FRCH ratio; thus, the family of solutions was represented by two surfaces in three-dimensional space. We extended the study to a smaller alveolar slope (0.6% N2/liter), assuming that the total slope (1.2% N2/liter) was partially caused by diffusion-convection interaction. We also studied a three-compartment lung as indicative of a multicompartmental lung. The results are discussed in relation to experimentally confirmed P-V heterogeneity. Granting our basic assumptions of P-V heterogeneity, the real physical lung characteristics may be a subsection of the range of theoretical solutions described herein.

Adult↗

PubMed1993

Computer methods in neuroanatomy: determining mutual orientation of whole neuronal arbors.

In most neurons orientation can be recognized because their arbors are more or less polarized and/or flattened. These are morphological characteristics of great functional importance. This paper deals with three-dimensional display and mathematical definition of orientation planes and vectors in whole arbors. An orientation plane can be derived from the flattest rectangular prism with which it is possible to enclose the arbor, or may be found by best-fit least square determination (based on all digitized points of the arbor). Both approaches allow description and comparison, in quantitative terms, of the orientation of neurons under various normal, pathological or experimental conditions.

Computer Graphics↗

PubMed1995

Virtual reality and telepresence for military medicine.

The profound changes brought about by technology in the past few decades are leading to a total revolution in medicine. The advanced technologies of telepresence and virtual reality are but two of the manifestations emerging from our new information age; now all of medicine can be empowered because of this digital technology. The leading edge is on the digital battlefield, where an entire new concept in military medicine is evolving. Using remote sensors, intelligent systems, telepresence surgery and virtual reality surgical simulations, combat casualty care is prepared for the 21st century.

Artificial Intelligence↗

PubMed1995

The responsive workbench: a virtual working environment for physicians.

The paper describes the concept of the Responsive Workbench (RW). This virtual environment was designed to support end users working on desks, workbenches, and tables as physicians, architects and scientists with an adequate human-machine interface. We attempt to construct a task-driven interface for this class of users by working in an interdisciplinary team from the beginning. The system is explained and evaluated along three medical applications: medical education, a cardiological tutorial with a simulation system for ultrasonographic examinations of the heart and surgery planning. Virtual objects are located on a real "workbench". The objects, displayed as computer generated stereoscopic images are projected onto the surface of a table. The participants operate within a non-immersive virtual environment. A "guide" uses the virtual environment while several observers can also watch events by using shutter glasses. Depending on the application, various input and output modules can be integrated, such as motion, gesture and speech recognition systems which characterize the general trend away from the classical multimedia desktop interface. The RW is compared with other common virtual reality systems as head mounted displays. First experiences of the collaborators are drawn and future enhancements are proposed.

Computer Graphics↗

PubMed1995

Virtual reality for physically disabled people.

This paper demonstrates how physically disabled people can benefit from the innovative virtual reality techniques. Several specific examples show the applicability of virtual reality to the therapy and rehabilitation of people with various disabilities. In addition, the paper describes how physicians can use virtual reality as an advanced visualization tool for the diagnosis of physical disabilities. Finally, possible display techniques and input devices for diagnosis and rehabilitation purposes are discussed briefly.

Attitude of Health Personnel↗