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PubMed1989

[Clinico-pathogenetic substantiation of medical tactics in combined benign hyperplastic processes in the uterus of patients of reproductive age].

The definition of concomitant benign hyperplastic diseases of the uterus relates to the abnormalities of the female reproductive system which are accompanied with a simultaneous development of uterine hyperplasias or endometrial polyps, myomas and/or endometriosis. The investigation of 290 patients of reproductive age revealed a multifactorial origin of the aforementioned diseases. Anamnestic, gynecological, dermatoglyphic, hormonal and receptor investigation techniques used in parallel with a routine general clinical examination evidenced systemic lesions and defined clinical and pathogenetic differences in the conditions associated with hyperplasia or endometrial polyps. The authors substantiated the use of various methods in the system of treatment: the use of nonsteroidal drugs with gestagen properties and cryogenic application to the walls of the uterus.

Adult↗
PubMed1993

Typing of serum-soluble HLA-B27 antigen by ELISA.

An ELISA using serum as soluble HLA antigen source was developed for HLA-B27 typing. Two sandwich assays were run in parallel. The first assay utilized a monoclonal antibody (mAb) reacting with a determinant expressed by both HLA-B7 and B27 antigens; the other assay utilized a mAb reactive with HLA-B7 antigens but not with HLA-B27 antigens. After incubation with serum samples, bound HLA antigen was detected using an anti-beta 2m antibody conjugated to peroxidase and a chromogenic substrate. Absorbance of each well was measured at 490 nm. Based on analysis of absorbances obtained with panels of specimens of known HLA phenotypes, a mathematical algorithm was developed to derive the specimen HLA-B27 phenotype from its ELISA absorbance values. Despite the lack of monospecific mAb, an accurate HLA-B27 typing was possible. 362 specimens (including 151 HLA-B27-positive) were tested. Agreement between microlymphocytotoxicity and ELISA was 99.2%. No correlation between the level of HLA-B27 antigen reactivity and the amount of total HLA class I antigen in serum was observed. This report demonstrates the possibility of using serum-soluble HLA antigen and ELISA technology for histocompatibility testing. The assay offers several significant advantages over microlymphocytotoxicity: no need for cell preparation, batch testing capabilities and objective, reproducible interpretation of results.

Algorithms↗
PubMed1996

Local computed tomography via iterative deblurring.

X-ray computed tomography is a major imaging modality. An iterative deblurring method is adapted for local reconstruction in parallel-beam and cone-beam geometries, utilizing only x-rays passing through a region of interest. The feasibility is demonstrated in numerical simulation with noise-free and noisy projection data. The iterative deblurring method has the theoretical advantages of maintaining nonnegativity, converging monotonically and minimizing Csiszàr's I-divergence.

Algorithms↗
PubMed1996

Determination of spinal facet joint loads from extra articular strains--a theoretical validation.

Loads on the facet joints of the lumbar spine may play a role in low back pain. Abnormal loading of the facets, either primarily or as a consequence of disc degeneration, may accelerate their degeneration. Study of these phenomena is difficult, since here are few methods for a direct measure of facet forces occurring in vivo. The authors developed a method for the direct measure of facet forces in a canine animal model of spine disease using strain gages. The method used empirical calibration of the strain gages, which was used to reduce experimental strain output to facet force during function. In this Technical Note, a theoretical model is formulated, solved and validated which gives a theoretical basis for the data reduction method. The facet is modeled as a cantilevered plate and deformations, as function of applied normal load, solved for using a finite difference method. The model is validated by comparison with two experiments with strain-gaged facets. Results from the model show that a minimum of three strain gages is required to determine uniquely the location and magnitude of an applied load to the facet, and that at least two gages should be placed in the region where the cranial articular process joins the pedicle with the gage axis parallel to that of the process. Plate surface strains were found to be insensitive to changes in the area of the applied loads, for a given resultant force magnitude. The method may be useful in other applications in which resultant force magnitude and location need to be measured on plate-like structures.

Algorithms↗
PubMed1992

Grand challenges in biomedical computing.

Advances in computing technology (both algorithms and hardware) over the next several years promise to make increasingly sophisticated computer modeling of biomedical phenomena a routine part of biomedical research. Improvements in both the absolute speed of processors and in their programming and graphics interfaces will allow nonexpert users to bring computing power equivalent to the supercomputers of a few years ago to bear on routine research problems and to display complex data in understandable ways (visualization). Although biomedical applications have traditionally not driven the leading edge of computing and supercomputing, such applications are increasingly being ported to advanced parallel and vector processors. This paper summarizes the current state of biomedical computing, citing examples of the best practice in research today. A number of projects enabled by advanced computing from various subdisciplines are described. Trends in technology for both inexpensive (workstation) and high-end computing (vector supercomputers and parallel processors) are cited; the implications of these for biomedical computing are discussed. "Grand challenges" in biomedical computing, i.e., computational problems of major scientific importance that are beyond our current capabilities but that might be achieved in a 5-year time frame, are outlined.

Attitude to Computers↗
PubMed1990

An optimal control model for maximum-height human jumping.

To understand how intermuscular control, inertial interactions among body segments, and musculotendon dynamics coordinate human movement, we have chosen to study maximum-height jumping. Because this activity presents a relatively unambiguous performance criterion, it fits well into the framework of optimal control theory. The human body is modeled as a four-segment, planar, articulated linkage, with adjacent links joined together by frictionless revolutes. Driving the skeletal system are eight musculotendon actuators, each muscle modeled as a three-element, lumped-parameter entity, in series with tendon. Tendon is assumed to be elastic, and its properties are defined by a stress-strain curve. The mechanical behavior of muscle is described by a Hill-type contractile element, including both series and parallel elasticity. Driving the musculotendon model is a first-order representation of excitation-contraction (activation) dynamics. The optimal control problem is to maximize the height reached by the center of mass of the body subject to body-segmental, musculotendon, and activation dynamics, a zero vertical ground reaction force at lift-off, and constraints which limit the magnitude of the incoming neural control signals to lie between zero (no excitation) and one (full excitation). A computational solution to this problem was found on the basis of a Mayne-Polak dynamic optimization algorithm. Qualitative comparisons between the predictions of the model and previously reported experimental findings indicate that the model reproduces the major features of a maximum-height squat jump (i.e. limb-segmental angular displacements, vertical and horizontal ground reaction forces, sequence of muscular activity, overall jump height, and final lift-off time).

Biomechanical Phenomena↗
PubMedDate not supplied

Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia.

PURPOSE: To compare the safety and efficacy of radial keratotomy (RK) and photorefractive keratectomy (PRK) to correct myopia. METHODS: In this randomized, prospective, parallel-group study, 33 patients with bilateral myopia of 1.00 to 5.00 diopters (D) had PRK in one eye and RK in the other. The order of surgeries and treatment assignments were randomized, and the bilateral surgeries were within 1 week for each patient. Data were collected using standardized procedures. Clinical measurements and satisfaction surveys were taken in masked fashion. RESULTS: Eyes that had PRK had statistically significantly more residual myopia than RK-treated eyes at 3, 6, and 12 months postoperatively. This result was attributed to the use of an older excimer laser PRK algorithm that was used at the initiation of the study. No eye that had PRK was overcorrected by 0.50 D or more at 1 year postoperatively, while seven eyes that had RK were overcorrected by at least 0.50 D and six were overcorrected by 1.00 D. Eyes that had PRK had a statistically significant mean shift in the myopic direction between 6 and 12 months postoperatively; two RK eyes had hyperopic shifts of 1.00 D. Three RK eyes and two PRK eyes failed to achieve an uncorrected visual acuity of 20/40 or better by 12 months postoperatively. No eye lost any best corrected visual acuity. CONCLUSION: The two procedures were comparably safe and effective in treating mild to moderate myopia under this protocol. Eyes that had PRK were somewhat more myopic at 1 year after surgery, attributable to the older PRK ablation algorithm. Adoption of newer (current) laser algorithms has improved the predictability of PRK. There was also evidence of reduced variability of outcome in the PRK group. The PRK eyes did not exhibit hyperopic shifts during the 1 year follow-up.

Adolescent↗
PubMed1981

Analysis and predication of structural motifs in the glycolytic enzymes.

Protein crystallography has determined the three-dimensional structures of 10 of the 13 enzymes of the glycolytic pathway. Diagrams and details of these enzyme structures are given in the paper. Most of the enzyme domains are variations and extensions of a many (4--9)-stranded, predominantly or totally parallel, beta-sheet that is shielded from solvent by alpha-helices (i.e. alpha/beta structures). There are strong structural similarities between the domains of some, but not all, of the enzymes. In particular the dinucleotide binding fold of lactate dehydrogenase and the beta-barrel of triose phosphate isomerase are found in other domains. General rules governing the topology and packing of alpha-helices against a beta-sheet provide a basis for the combinatorial prediction of the tertiary fold of glycolytic domains from their amino acid sequence and observed secondary structure. The predication algorithm demonstrates that there are severe restrictions on the number of possible structures. However, these restrictions do not fully explain some of the remarkable structural similarities between different enzymes that probably result from evolution from a common ancestor.

Animals↗
PubMed1997

X-ray crystal structure of cytotoxic oxidized cholesterols: 7-ketocholesterol and 25-hydroxycholesterol.

The cytotoxic cholesterol derivative, 7-ketocholesterol, crystallizes in a monoclinic unit cell, space group P2(1) with a = 11.405 A, b = 6.288 A, c = 35.393 A and beta = 92.75 degrees (Z = 4). Its room temperature crystal structure was solved by direct methods, i.e., the minimal principle via the Shake-and-Bake (SnB) algorithm. In contrast to the continuous chain pattern found for the cholesterol monohydrate structure, hydrogen bonding in the 7-ketocholesterol structure is localized to specific sites via one water molecule that forms linkages between two O3 hydroxyl groups and one keto oxygen. The final weighted R factor for 4562 reflections was 0.144. The 25-hydroxycholesterol also crystallizes in a monoclinic unit cell (P2(1)), with a = 10.840 A, b = 14.533 A, c = 16.093 A and beta = 95.91 degrees (Z = 4). The low temperature structure was solved by DIRDIF. In this instance, molecular packing is anti-parallel in layers stabilized by hydrogen bonding networks via both hydroxyl functions, differing both from cholesterol monohydrate and the 7-ketocholesterol. The final weighted R-factor for 6566 reflections was 0.034. Functional differences of the oxysterols therefore, may be expressed by observed variations in the molecular packing and geometry.

Crystallization↗
PubMed1994

An architecture for EEG signal processing and interpretation during sleep (ESPIS).

The project's aim is to develop a dedicated workstation in order to process multiple channels of electrophysiological signals in real-time during sleep. In ESPIS we are aiming to define both an architecture and an environment for EEG signal interpretation in medicine based on computer science gold standards (Unix, XWindow, Motif). Signal processing and pattern recognition analysis are provided by parallel processing on a specific developed acquisition architecture (DSP) based on transputers. The main result is a high performance prototype demonstrating signal interpretation during sleep which has already been tested in a medical environment. The overall specifications allow this biomedical device to be extended to other types of medical signals.

Algorithms↗
PubMed1995

An approach to validation of a leg simulation by the comparison of two dynamic models.

The dynamics of a jointed leg were simulated using two different models, one based on a recursive Newton-Euler method and one on a closed-form Lagrange method. To validate the models, the simulations were run in parallel and the intermediate steps and output of the two methods were compared to one another to reveal the presence and locations of errors. Sources of error and the use of this method for the detection of errors are discussed. Some errors could not have been detected using only a single simulation.

Acceleration↗
PubMed1991

A distributed-parameter model of the myelinated nerve fiber.

This paper presents a new model for the characterization of electrical activity in the nodal, paranodal and internodal regions of isolated amphibian and mammalian myelinated nerve fibers. It differs from previous models in the following ways: (1) in its ability to incorporate detailed anatomical and electrophysiological data; (2) in its approach to the myelinated nerve fiber as a multi-axial cable; and (3) in the numerical algorithm used to obtain distributed model equation solutions for potential and current. The morphometric properties are taken from detailed electron microscopic anatomical studies (Berthold & Rydmark, 1983a, Experientia 39, 964-976). The internodal axolemma is characterized as an excitable membrane and model-generated nodal and internodal membrane action potentials are presented. A system of describing equations for the equivalent network model is derived, based on the application of Kirchoff's Current Law, which take the form of multiple cross-coupled parabolic partial differential equations. An implicit numerical integration method is developed and the numerical solution implemented on a parallel processor. Non-uniform spatial step sizes are used, enabling detailed representation of the nodal region while minimizing the number of total segments necessary to represent the overall fiber. Conduction velocities of 20.2 m sec-1 at 20 degrees C for a 15 microns diameter amphibian fiber and 57.6 m sec-1 at 37 degrees C for a 17.5 microns diameter mammalian fiber are achieved, which agrees qualitatively with published experimental data at similar temperatures (Huxley & Stämpfli, 1949, J. Physiol., Lond. 108, 315-339; Rasminsky, 1973, Arch, Neurol. 28, 287-292). The simulation results demonstrate the ability of this model to produce detailed representations of the transaxonal, transmyelin and transfiber potentials and currents, as well as the longitudinal extra-axonal, periaxonal and intra-axonal currents. Also indicated is the potential contribution of the paranodal axolemma to nodal activity as well as the presence of significant longitudinal currents in the periaxonal space adjacent to the node of Ranvier.

Action Potentials↗
PubMed1998

Porcine cerebroside sulfate activator (saposin B) secondary structure: CD, FTIR, and NMR studies.

Cerebroside sulfate activator protein (CSAct or saposin B) is one of a group of heat stable, low-molecular-weight proteins that appear to share a common structural motif. These have been referred to as saposin-like proteins and are thought to share a multiple amphipathic helical barrel structure with a conserved pattern of disulfide linkages. Porcine kidney CSAct was prepared in high purity and consisted of three major glycosylated subforms. The protein was studied by physical-chemical methods and evaluated by various methods for structural prediction. All suggest that CSAct has high amounts of alpha-helical conformation and little if any beta-sheet. Circular dichroism (CD) studies indicate 45-50% helical conformation depending on buffer and temperature. There was only a moderate loss in helical content with increasing temperature and no indication of thermal denaturation. Fourier transform infrared spectroscopy (FTIR) measurements on deuterium hydrated self-films also indicated a predominantly helical structure. Helical axis orientation was investigated by both oriented CD and FTIR dichroism, which suggested that the helical axes were roughly parallel and oriented along the axis of the surface on which the self-films had been deposited. One-dimensional nuclear magnetic resonance spectra showed large chemical shift dispersion, indicating a defined tertiary structure with little variation between 6 and 85 degrees C. NOESY spectra failed to show the strong NOE cross peaks expected for a highly helical conformation. This may indicate short-term conformational flexibility within the helices or molecular aggregation at the high protein concentrations employed. These observations are consistent with the 3-4-helix bundle motif suggested for saposin-like proteins by various predictive algorithms.

Algorithms↗
PubMed1988

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to human alpha-, beta- and gamma-thrombin; a kinetic and thermodynamic study.

Kinetic and thermodynamic parameters for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to human alpha-, beta- and gamma-thrombin have been determined, between 5 and 45 degrees C, at pH 7.5. BPTI-binding properties to human thrombins have been analyzed in parallel with those of serine (pro)enzymes acting on cationic and non-cationic substrates, with particular reference to the bovine beta-trypsin/BPTI system. The observed binding behaviour of BPTI to human alpha-, beta- and gamma-thrombin has been related to the inferred stereochemistry of the enzyme/inhibitor contact region(s).

Algorithms↗
PubMed1993

A hardware efficient cascadable chip set for ANN's with on-chip backpropagation.

In this paper, an analogue, cascadable, CMOS chip set for artificial neural networks is presented. The chip set (a synapse chip and a neuron chip) offer on-chip back-propagation learning in a fully parallel, layered, feedforward network of arbitrary size and topology. The learning scheme is implemented with no extra circuits at the synapse sites (compared to the system without the learning scheme) and extra circuits of a complexity only about the same as the neurons at the neuron sites. Also, no additional wiring is required by the learning scheme. Measurements on an experimental chip set are presented.

Algorithms↗
PubMed1997

Developments in cardiovascular ultrasound: Part 1: Signal processing and instrumentation.

One of the major contributions to the improvement of spectral Doppler and colour flow imaging instruments has been the development of advanced signal-processing techniques made possible by increasing computing power. Model-based or parametric spectral estimators, time-frequency transforms, station-arising algorithms and spectral width correction techniques have been investigated as possible improvements on the FFT-based estimators currently used for real-time spectral estimation of Doppler signals. In colour flow imaging some improvement on velocity estimation accuracy has been achieved by the use of new algorithms but at the expense of increased computational complexity compared with the conventional autocorrelation method. Polynomial filters have been demonstrated to have some advantages over IIR filters for stationary echo cancellation. Several methods of velocity vector estimation to overcome the problem of angle dependence have been studied, including 2D feature tracking, two and three beam approaches and the use of spectral width in addition to mean frequency. 3D data acquisition and display and Doppler power imaging have also been investigated. The use of harmonic imaging, using the second harmonic generated by encapsulated bubble contrast media, seems promising particularly for imaging slow flow. Parallel image data acquisition using non-sequential scanning or broad beam transmission, followed by simultaneous reception along a number of beams, has been studied to speed up 'real-time' imaging.

Blood Flow Velocity↗
PubMed1994

A variable-resolution rotate-only computed tomography scanner.

The Rotoscan is a computed tomography scanner that combines the advantages of variable geometric resolution and adjustable size of measurement diameter of translate-rotate scanners with the improved speed of rotate-only scanners. Because of the small number of only 26 detectors used for this scanner, a special data collection scheme of multiple rotations with interleaved detector positions was employed. In order to avoid angular data interpolation after reordering of the projections from the fan- to a parallel-beam geometry, the detectors were incrementally moved at a right angle to the centerline of the fan rather than rotated about the source. The measurement time of 40 s for one cross-section is comparable to that of second-generation systems. However, for longer measurement diameters, the measurement time for second-generation systems increases, whereas that of the Rotoscan remains constant.

Algorithms↗
PubMed1994

Nutrition support, supplementation, and replacement.

Nutrition support in acute, chronic, or home care settings can be implemented successfully by the well-informed primary care physician, who often is the first to identify poor nutritional health in his or her patients. Using established protocols for the identification or of risk factors and indicators of malnutrition, specific alerts to the need for nutrition support are presented. The logical approach to nutrition support interventions through four stages representing the gradual increase in complexity and cost, paralleling the progressive inability to use regular foods and the gastrointestinal tract are discussed. Specific, practical measures that can be recommended and implemented by the primary care physician managing the older person are presented. The ethical, legal, and home health aspects of nutrition support in the care of the older American by the primary care physician are also reviewed.

Aged↗