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Biomedical subjects

E Barth

Publications and source records attributed to E Barth.

At least 19 recordsLinked to original sources
PubMed1998

Intrinsic two-dimensional features as textons.

We suggest that intrinsic two-dimensional (i2D) features, computationally defined as the outputs of nonlinear operators that model the activity of end-stopped neurons, play a role in preattentive texture discrimination. We first show that for discriminable textures with identical power spectra the predictions of traditional models depend on the type of nonlinearity and fail for energy measures. We then argue that the concept of intrinsic dimensionality, and the existence of end-stopped neurons, can help us to understand the role of the nonlinearities. Furthermore, we show examples in which models without strong i2D selectivity fail to predict the correct ranking order of perceptual segregation. Our arguments regarding the importance of i2D features resemble the arguments of Julesz and co-workers regarding textons such as terminators and crossings. However, we provide a computational framework that identifies textons with the outputs of nonlinear operators that are selective to i2D features.

Discrimination, Psychological↗
PubMed1998

Determination of 13CO2/12CO2 ratio by IRMS and NDIRS.

Breath tests using 13C-labelled substrates require the measurement of 13CO2/12CO2 ratio in breath gas samples. Next to isotope ratio mass spectrometry (IRMS), which is very sensitive but also complex and expensive, alternatively isotope selective nondispersive infrared spectrometry (NDIRS) can be used to determine the 13CO2/12CO2 ratio in expired breath. In this study we compared NDIRS- with IRMS-results to investigate whether the less expensive and very simply to operate NDIRS works as reliable as IRMS. For this purpose we applicated 1- 13C-Phenylalanine to patients with advanced liver cirrhosis and healthy volunteers and took duplicated breath samples for IRMS and NDIRS at selected time points. Our data show a good correlation between these two methods for a small number of samples as required for simple breath tests. Longer series, where repeated measurements are required on the NDIRS instrument lead to a decreasing correlation. This indicates the superiority of IRMS concerning 13CO2-kinetics over longer time periods.

Breath Tests↗
PubMed1997

Neural network models and the visual cortex: the missing link between orientation selectivity and the natural environment.

Orientation selectivity is a basic property of neurones in the visual cortex of higher vertebrates. Such neurones can be seen to act as 'feature detectors', which provide an efficient cortical representation of the outside world. More recently, the removal of correlations between the signals of cortical neurones has been suggested as suitable theoretical concept for explaining the development of receptive fields. Corresponding neural network simulations yielded oriented 'receptive field' structures resembling those observed by neurophysiologists. The findings suggest that the 'decorrelation approach' can provide a causal relationship between characteristics of the physical world and brain function. However, we were able to reveal a basic deficit of the decorrelation approach which we illustrate by the construction of two artificial 'worlds', a 'Gaussian' one and an 'orientation-only' one. We show that, according to the decorrelation approach, oriented environmental features would be neither necessary nor sufficient for the development of oriented receptive fields. Thus the link between environmental structure and cortical orientation selectivity still awaits a theoretical explanation.

Environment↗
PubMed1997

Biomolecular dynamics at long timesteps: bridging the timescale gap between simulation and experimentation.

Innovative algorithms have been developed during the past decade for simulating Newtonian physics for macromolecules. A major goal is alleviation of the severe requirement that the integration timestep be small enough to resolve the fastest components of the motion and thus guarantee numerical stability. This timestep problem is challenging if strictly faster methods with the same all-atom resolution at small timesteps are sought. Mathematical techniques that have worked well in other multiple-timescale contexts--where the fast motions are rapidly decaying or largely decoupled from others--have not been as successful for biomolecules, where vibrational coupling is strong. This review examines general issues that limit the timestep and describes available methods (constrained, reduced-variable, implicit, symplectic, multiple-timestep, and normal-mode-based schemes). A section compares results of selected integrators for a model dipeptide, assessing physical and numerical performance. Included is our dual timestep method LN, which relies on an approximate linearization of the equations of motion every delta t interval (5 fs or less), the solution of which is obtained by explicit integration at the inner timestep delta tau (e.g., 0.5 fs). LN is computationally competitive, providing 4-5 speedup factors, and results are in good agreement, in comparison to 0.5 fs trajectories. These collective algorithmic efforts help fill the gap between the time range that can be simulated and the timespans of major biological interest (milliseconds and longer). Still, only a hierarchy of models and methods, along with experimentational improvements, will ultimately give theoretical modeling the status of partner with experiment.

Algorithms↗
PubMed1996

Generalization of form in visual pattern classification.

Human observers were trained to criterion in classifying compound Gabor signals with symmetry relationships, and were then tested with each of 18 blob-only versions of the learning set. Generalization to dark-only and light-only blob versions of the learning signals, as well as to dark-and-light blob versions was found to be excellent, thus implying virtually perfect generalization of the ability to classify mirror-image signals. The hypothesis that the learning signals are internally represented in terms of a 'blob code' with explicit labelling of contrast polarities was tested by predicting observed generalization behaviour in terms of various types of signal representations (pixelwise, Laplacian pyramid, curvature pyramid, ON/OFF, local maxima of Laplacian and curvature operators) and a minimum-distance rule. Most representations could explain generalization for dark-only and light-only blob patterns but not for the high-thresholded versions thereof. This led to the proposal of a structure-oriented blob-code. Whether such a code could be used in conjunction with simple classifiers or should be transformed into a propositional scheme of representation operated upon by a rule-based classification process remains an open question.

Adult↗
PubMed1995

In situ detection, by spin trapping, of hydroxyl radical markers produced from ionizing radiation in the tumor of a living mouse.

Hydroxyl radicals are thought to be responsible for the toxicity associated with ionizing radiation in tissues. Measurements of hydroxyl radicals generated by ionizing radiation in cellular systems have failed thus far to elucidate higher-level homeostatic responses to this and other reactive oxygen species. Careful assessment of prior indirect hydroxyl radical assays in living tissues indicates that they are prone to a variety of artifacts, making all but the most qualitative relationships difficult to establish. This paper describes the detection of hydroxyl radicals produced during radiation in the leg tumor of a living mouse, where the free radicals evolve; detection uses low-frequency electron paramagnetic resonance in combination with in vivo spin trapping. To our knowledge, this is the first report of such a direct measurement of free radical production in the tissues of a living animals.

Animals↗
PubMed1994

Oxymetry deep in tissues with low-frequency electron paramagnetic resonance.

We have measured the oxygen concentration in the body water of murine FSa and NFSa fibrosarcomas using a new method for quantitative oxygen concentration determination deep in the tissues of a living animal. The measurement uses unusually low-frequency electron paramagnetic spectroscopy sensitive to substrate 7 cm deep in tissue, partially deuterated spin probes (spin labels of molecular mass 195, approximating that of glucose) whose distribution compartment can be targeted with facile adduct substitution, and novel analytic techniques. We show that the water-compartment oxygen concentration of the tumors decreases as the tumor size increases and also shows a trend to decrease as radiobiologic hypoxia increases. An oxymetric spectral image of the tumor is presented. The technique will improve with larger human tissue samples. It provides the potential to quantitatively assess tissue hypoxia in ischemic or preischemic states in stroke and myocardial infarction. It will allow direct assessment of tumor hypoxia to determine the usefulness of radiation and chemotherapy adjuvants directed to hypoxic cell compartments.

Animals↗
PubMed1992

Ultrastructural quantitation of mitochondria and myofilaments in cardiac muscle from 10 different animal species including man.

The ultrastructural quantitative composition of normal myocardial cells has been studied in 10 different species: man, dog, pig, cat, rabbit, ferret, guinea-pig, rat, mouse, and bat. Volume densities of mitochondria, myofibrils, and cytoplasm were determined using morphometry. It was found that the content of mitochondria differs in various species ranging between 22.0-37.0%. It is a very specific and constant value for any particular species, the smallest having the highest content. A close correlation exists between the mitochondrial volume density, heart rate and the rate of basal oxygen consumption in any group of animals. The myofibrillar volume density shows no species variability. It was about 60.0% in all species. It is concluded that the mitochondrial volume density is a good indicator of the oxidative capacity of cardiac muscle and that the species specific normal ultrastructural myocyte composition should be a useful baseline in pathophysiological studies of the heart in various animals.

Actin Cytoskeleton↗
PubMed1991

Multicentre evaluation of the blood gas-electrolyte-analyser "BGE".

A multicentre evaluation of the blood gas-electrolyte-haematocrit-analyser BGE (Fa. Instrumentation Laboratory), following as far as possible the ECCLS guidelines for multicentre evaluation of blood gas analysers, was performed by three laboratories. The rules of the evaluation protocol were extended to the electrolyte and haematocrit determinations. The BGE proved to be easy to operate and maintain. The stability of the measuring system was good. The within-run imprecision of all electrodes was excellent. The same applies to the between-day imprecision, except for the calcium measurements. The systematic deviation of the gas electrodes was very small. Comparison studies revealed clinically significant deviations only for ionized calcium. Some suggestions for further improvements are made.

Blood Gas Analysis↗
PubMed1991

An analysis of polyethylene thickness in modular total knee components.

Polyethylene wear has become an important consideration in total knee arthroplasty. The actual polyethylene thickness of modular tibial components is not widely known and may be critical to long-term survival of implants. The actual polyethylene thickness of eight widely used tibial components was measured and found to vary significantly among manufacturers, even though the combined thickness of metal tray and polyethylene was similar. No component met current recommendations for minimum polyethylene thickness.

Biomechanical Phenomena↗
PubMed1990

Animal model for evaluating bone repair with and without adjunctive hyperbaric oxygen therapy (HBO): comparing dose schedules.

The effect of hyperbaric oxygen (HBO) on the healing of standardized metaphyseal defects in the cortices of rat femurs was studied. The question was whether a known total amount of HBO given twice a day (BID) would have a different effect than once a day (QD) treatments. A microvascular casting technique was developed whereby vessel ingrowth at the repair site could be monitored using scanning electron microscopy (SEM). Bone repair morphology was evaluated by light microscopy (LM) and various tissue components were quantified by histomorphometry (HM). Animals were sacrificed 1, 2, 3, or 5 weeks postoperatively. SEM revealed that endosteal bone ingrowth was totally responsible for the repair of the cortical defects. Moreover, endosteal vessel ingrowth did not differ between controls and either group of HBO treated animals. LM displayed enchondral ossification in controls and BID treated animals and a pronounced osteoclastic activity in the latter group throughout the repair process. By contrast the QD treated group healed by primary ossification. Judged by the HM data, QD treatment appeared to accelerate bone repair and vessel ingrowth compared to controls, while BID treatment seemed to retard these processes.

Animals↗
PubMed1990

Histologic comparison of ceramic and titanium implants in cats.

This study compared the reparative processes around cylindrical glass-ceramic-coated and pure titanium implants placed in feline femurs. Six weeks after implant placement, bone specimens with inserted implants were prepared for histologic examination including histomorphometric quantification of the relative implant surface areas that were in contact with bone. The glass-ceramic implants were surrounded by a 0.2- to 0.5-mm envelope of fibrous connective tissue [corrected]. By contrast, the major part of the titanium implants (81% +/- 5%) was in direct contact with living lamellar or woven bone. Thus, titanium and glass ceramic evoked different reparative processes when implanted in bone, and only the titanium implants appeared to become osseointegrated.

Animals↗
PubMed1989

In vitro and in vivo comparative colonization of Staphylococcus aureus and Staphylococcus epidermidis on orthopaedic implant materials.

Clinically, Staphylococcus aureus appears to be the dominant organism associated with infected metal implants, whereas coagulase-negative staphylococcal strains are more frequently isolated from infected polymer implants. We reproduced this trend experimentally in vitro and in vivo. Discs of a titanium alloy, poly(methyl methacrylate) and ultra-high molecular weight polyethylene were exposed to a clinical isolate of Staphylococcus aureus or either of two strains of Staphylococcus epidermidis. Within 1 h Staphylococcus aureus was always the most rapid colonizer regardless of biomaterial. However, after 8 to 24 h, Staphylococcus aureus was present in higher numbers on metal and Staphylococcus epidermidis on polymers. Moreover, the exopolysaccharide produced by Staphylococcus epidermidis appeared to offer an effective protection against host defences in vivo.

Alloys↗
PubMed1989

Implant infection.

Explore the source record for details and available documents.

Bacterial Infections↗
PubMed1989

Effects of extracellular slime produced by Staphylococcus epidermidis on oxidative responses of rabbit alveolar macrophages.

Bacterial slime produced in mass cultures of the RP 12 strain of Staphylococcus epidermidis was extracted with 4 M guanidine-HCl plus 0.05 M sodium acetate and 0.5% CHAPS, concentrated, dialyzed, and subjected to separation on DEAE sephacel columns. Three fractions, I-2A, I-2B, and I-4, were eluted with linear gradients of NaCl. Fractions I-2A and I-2B were alcian blue positive, whereas I-4 was alcian blue negative but the most electronegative fraction. The crude polysaccharide fraction and the three purified fractions were incubated individually for 2.5 or 20 h with normal rabbit alveolar macrophages (AM) to determine their effect on a subsequent PMA-induced oxidative burst. The crude fraction (50-200 micrograms/mL) and I-2B (50-200 micrograms/mL) primed the AM to give approximately a threefold increase in the PMA-induced burst after 2.5 h incubation. In contrast, a 20-h incubation resulted in a 30-40% inhibition of the PMA-induced burst with AM incubated with the same concentrations of the crude, I-2A, or I-2B fractions. Fraction I-4 had no detectable effect. The fractions also were tested to determine if they could elicit an oxidative burst in BCG-immune AM. None of the fractions (up to 500 micrograms/mL) elicited a significant oxidative burst even though BCG-immune AM yielded a PMA-induced burst 100 times that observed with normal resident AM. These data suggest that slime from S. epidermidis can impair the PMA-induced oxidative burst of normal AM during a 20-h incubation period and could explain in part why host defenses are compromised by slime-producing S. epidermidis.

Animals↗
PubMed1989

The use of adjunctive hyperbaric oxygen in treatment of orthopedic infections and problem wounds: an overview and case reports.

We summarize indications, contraindications, and therapeutic guidelines for the use of adjunctive hyperbaric oxygen therapy (HBO) in problem wounds and selected orthopaedic infections. Three typical cases that all were successfully treated with HBO are presented: a chronic osteomyelitis which was a sequela to an open tibia fracture, a second- and third-degree burn injury of the entire lower extremity, and a case of chronic osteomyelitis in an insulin-dependent diabetic.

Adult↗