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Biomedical subjects

K Polgár

Publications and source records attributed to K Polgár.

At least 19 recordsLinked to original sources
PubMed2006

RSA-measured inducible micromotion and interface modeling with finite element methods.

Osteolysis is the main cause of aseptic loosening and stem failure. The mechanism that leads to osteolysis is poorly understood; pressure generation caused by reversible stem micromotion may play an important role. We aimed to determine whether dynamically inducible micromotion occurs in vivo at the prosthesis-cement interface and to use these data to develop and confirm a finite element representation of this interface. Dynamically inducible micromotion was measured using radiostereometric analysis in 21 hips implanted with an Exeter stem, at 3 months and 12 months postoperatively, by changing loading from double-leg stance to single-leg stance. Dynamically inducible micromotion occurred at 3 and 12 months; similar micromotion was observed at both time points. At 3 months the head of the stem was displaced posteriorly (0.10 +/- 0.16 mm) and inferiorly (0.08 +/- 0.12 mm) on loading. A Coulomb friction nonbonded representation of the stem-cement interface was used to fit the clinically measured dynamically inducible micromotion. The final finite element model predicted gap opening and closing between the implant and the mantle. This may be a mechanism for generating pressure and distributing wear debris, which are believed to important contributors to failure.

Aged↗
PubMed2003

Nonuniform dynamic gratings in photorefractive media with nonlocal response.

The amplitude of the phase dynamic grating is a nonuniform space distributed in photorefractive crystals with nonlocal response as a result of energy transfer between the interacted waves. The dynamical process of grating formation in the case of transmission two- and four-wave mixing is described by the damped sine-Gordon equation that governs the soliton propagation. A stationary soliton solution for the grating amplitude profile was obtained. Experiments on observation of a nonuniform distribution of the grating amplitude through the crystal volume are presented. It is experimentally shown that the changes of the grating amplitude profile in dependence of input intensity ratio match the solutions of the damped sine-Gordon equation in steady state. The diffraction efficiency of energy transfer is determined by the value of the integral under the grating amplitude profile. The soliton profile is altered with changing input intensity ratio of recorded beams. It provides the effect of diffraction efficiency management by changing the half-width and the position of the soliton. The theory predicts a multisoliton behavior in reversible media with strong amplification gain that leads to auto-oscillations of output wave intensities.

Journal Article↗
PubMed2003

Development and numerical validation of a finite element model of the muscle standardized femur.

The human femur is one of the parts of the musculo-skeletal system most frequently analysed by means of the finite element (FE) method. Most FE studies of the human femur are based on computed tomography data sets of a particular femur. Since the geometry of the chosen sample anatomy influences the computed results, direct comparison across various models is often difficult or impossible. The aim of the present work was to develop and validate a novel three-dimensional FE model of the human femur based on the muscle standardized femur (MuscleSF) geometry. In the new MuscleSF FE model, the femoral attachment of each muscle was meshed separately on the external bone surface. The model was tested under simple load configurations and the results showed good agreement with the converged solution of a former study. In the future, using the validated MuscleSF FE model for numerical studies of the human femur will provide the following benefits: (a) the numerical accuracy of the model is known; (b) muscle attachment areas are incorporated in the model, therefore physiological loading conditions can be easily defined; (c) analyses of the femur under physiological load cases will be replicable; (d) results based on different load configurations could be compared across various studies.

Compressive Strength↗
PubMed2003

Strain distribution within the human femur due to physiological and simplified loading: finite element analysis using the muscle standardized femur model.

The aim of the current work was to study the effect of simplified loading on strain distribution within the intact femur using the Muscle Standardized Femur finite element model and to investigate whether the interaction between the intact human femur and the muscles which are attached to the bone surface could accurately be represented by concentrated forces, applied through the centroids of their attachment areas. An instant at 10 per cent of the gait cycle during level walking was selected as the reference physiological load case; nine load cases were analysed. Comparison of the calculated results for the physiological load case with muscle forces uniformly distributed over their attachment areas showed good agreement with in vivo measurements of strain values and femoral head displacement in humans. Simplified load cases generated unrealistic displacement results and high strain magnitudes, exceeding the physiological range. It was found that when muscles with large attachment areas are included in the model and the muscle forces are simplified, stress and strain distributions will be affected not only on the external bone surface in the vicinity of the load application node, but also on the internal surface of the cortical bone. However, applying muscle forces as concentrated loads at the centroids of the attachment areas can serve as first indicators of the physiological stress and strain levels, if results from nodes and elements in the vicinity of the load application nodes are discarded. Omitting muscle forces or fixing the femur in mid-shaft leads to large unphysiological strain values.

Compressive Strength↗
PubMed1996

Immune interferon gamma inhibits translational mobility of a plasma membrane protein in preimplantation stage mouse embryos: a T-helper 1 mechanism for immunologic reproductive failure.

OBJECTIVE: Immune interferon gamma adversely affects mouse embryo development and has been proposed as a mediator of reproductive failure involving T-helper 1 immunity. We hypothesized that one mechanism by which interferon gamma could exert an adverse effect on embryos was by altering plasma membrane organization and transmembrane protein mobility. STUDY DESIGN: The fluorescence photobleaching recovery technique was used to measure the effect of the T-helper 1 cytokine interferon gamma on the translational mobility of a specific embryonic surface glycoprotein recognized by the monoclonal antibody S75. RESULTS: Compared with controls interferon gamma significantly decreased the fractional mobility of fluorescein isothiocyanate S75 in one- and two-cell mouse embryos. CONCLUSION: Interferon gamma may alter plasma membrane domains or cytoskeletal organization in early-stage embryos. By restricting plasma membrane protein mobility interferon gamma could effect T-helper 1-mediated reproductive failure.

Abortion, Spontaneous↗
PubMed1994

Use of the translational mobility of a plasma membrane protein to assess fertilization of mouse oocytes and viability of mouse zygotes and two-cell embryos.

The fluorescence photobleaching recovery (FPR) technique was used to measure the translational mobility of a glycoprotein recognized by the monoclonal antibody (mAb) S75 in plasma membranes of mouse oocytes, zygotes, and two-cell embryos. Glycoprotein fractional mobility (f) was significantly decreased in membranes of unfertilized oocytes compared to zygotes or two-cell embryos (f values, 46 +/- 2 and 65 +/- 2%, respectively; p < 0.0001). Reduced apparent glycoprotein mobility was also observed in morphologically degenerated zygotes and two-cell embryos compared to viable zygotes and two-cell embryos (f values, 8 +/- 1 and 60 +/- 3%, respectively; p < 0.0001). These results indicate that the FPR technique can be used to assess oocyte fertilization and preimplantation embryonic viability. This method may be useful in the evaluation of embryonic viability following in vitro fertilization and in the detection of toxic effects of novel compounds on embryonic development.

Animals↗
PubMed1990

Modulation of dopamine-induced hypermotility following injection of various opioids into the nucleus accumbens.

The aim of the present work was to obtain some data on the eventual role of nucleus accumbens in the antidopamine action of some opioids. Classical neuroleptics are known to inhibit the dopamine-elicited hypermotility when injecting them into the nucleus accumbens of rats pretreated with MAO inhibitors. In the present study the effects of some opioids have been examined in this model. The opioids examined were morphine, a mu-selective classical opiate, D-Ala2, Nle5-enkephalin sulphonic acid (ES), a delta selective opioid peptide and D-Met2, Pro5-enkephalinamide (EA), a non-selective opioid peptide. Haloperidol and chlorpromazine have been used for comparison. EA and morphine, especially the former, potently antagonized the dopamine-induced hyperactivity, similarly to haloperidol and chlorpromazine. ES exerted biphasic effect, the initial inhibition was followed by potentiation of the dopamine-elicited excitation. Thus the order of potency was: EA greater than haloperidol approximately equal to morphine greater than chlorpromazine greater than EA. The data indicate that the antidopamine action of opioids might be mediated, at least in part, by mu-receptors in the nucleus accumbens.

Animals↗
PubMed1989

Characterization of rapidly adhering amniotic fluid cells by combined immunofluorescence and phagocytosis assays.

Culture of human amniotic-fluid cells from cases of fetal neural tube defects produces a population of rapidly adhering cells that were initially thought to be macrophages and later interpreted to be of neural origin. In this study double and triple labeling systems for the simultaneous detection of glial and macrophage differentiation marker antigens have been used to demonstrate that rapidly adhering cells cannot be considered a homogeneous population but instead represent two distinct cell types. One of these cell populations is of glial origin and shows specific staining for glial fibrillary acidic protein, while the other population is monocyte-derived macrophages which express marker antigens recognized by Leu M3, KiM7, and Dako antimacrophage monoclonal antibodies.

Amniotic Fluid↗
PubMed1988

Neutral-red uptake and expression of monocytic antigens in amniotic-fluid mononuclear phagocytes: evaluation of a novel approach for prenatal diagnosis of neural-tube defects.

In cases of fetal neural-tube defects macrophages are present in the amniotic fluid. We found that these viable phagocytic cells take up neutral-red and are easily identified as "red cells" by microscopic examination. This method is suitable for the rapid identification and counting of amniotic-fluid macrophages in suspension. We have studied 298 amniotic fluid samples. In the 226 normal cases studied, 0 to 1,200 macrophages per milliliter amniotic fluid have been found. In contrast, we found 1,250 to 99,000 macrophages per milliliter amniotic fluid in our 70 open neural tube defect (ONTD) cases. Statistical evaluation was performed to estimate the normal and pathologic ranges. Specificity and sensitivity of the neutral-red test and predictive value of positive and negative results have been calculated and presented in comparison with alpha-fetoprotein (AFP) determinations and ultrasonic methods. In 5 cases of anencephaly and 7 normal cases amniotic fluid cells were studied by immunocytochemistry: mononuclear cells present in the abnormal cases showed intense immunoreactivity for the Mo1 and Mo2 surface antigens of the phagocytic cell lineage.

Amniotic Fluid↗
PubMed1988

Immunobiological methods in the prenatal diagnosis and evaluation of foetal neural tube defects.

In cases of foetal neural tube defects (NTDs) macrophages are present in the amniotic fluid. These mononuclear cells were analysed with immunobiological methods: functional markers as Fc and C3b receptor-mediated phagocytosis and chemoluminescence have been studied. It was found that most of these pathognomic cells ingest haemolysin sensitized sheep red blood cells (sSRBCs) and zymosan (Mannozym) particles opsonized with fresh human serum. Amniotic fluid cell suspensions from pregnancies with and without foetal NTDs were stimulated by opsonized Mannozym; consistently higher chemoluminescence activities were found when open lesion was present. The evaluation of multiple functional markers is likely to provide a better basis for understanding the characteristics of amniotic fluid macrophages and may contribute to the prenatal diagnosis of NTDs.

Amniocentesis↗
PubMed1987

Modulation by enkephalin analogues and neuroleptics of apomorphine-induced stereotypy and turning behaviour in rats.

The aim of the present investigation was to examine which areas of the brain might mediate the anti-apomorphine action of some opioids, which were found previously to be active upon subcutaneous application. As the first step, the substances were injected intracerebroventricularly or into the nucleus accumbens, a mesolimbic region which is rich in dopamine, and the inhibition of stereotypy induced by apomorphine was quantified. In a separate group of animals (rats with unilateral lesion of the nigra) the antagonism of turning behaviour elicited by apomorphine was measured. Substances examined were morphine, a mu-selective opiate; D-Ala2,Nle5-enkephalin sulphonic acid (ES), a delta-selective opioid peptide; D-Met2,Pro5-enkephalinamide (EA), a highly potent but non-selective opioid; and two dopamine receptor blockers, haloperidol and chlorpromazine, for comparison. Examining the antagonism of turning behaviour induced by apomorphine, the order of potency was EA greater than haloperidol greater than morphine greater than ES approximately equal to chlorpromazine if injections of the substances were intracerebroventricular and EA greater than morphine much greater than haloperidol approximately equal to ES much greater than chlorpromazine when administered into the nucleus accumbens. The order of potency for the suppression of stereotypy induced by apomorphine was EA much greater than haloperidol greater than morphine greater than ES greater than chlorpromazine upon intracerebroventricular application and EA much greater than haloperidol greater than morphine ES greater than chlorpromazine if injected into the nucleus accumbens. The data indicate that endogenous opioids might inhibit the activity of dopamine in brain through the nucleus accumbens.

Animals↗
PubMed1986

Exencephaly in human fetuses.

In some anencephalic fetuses exposed neural tissue mass of varied size can be demonstrated. This is known as exencephaly. The authors diagnosed by ultrasound 10 typical exencephalic cases prenatally between 14 and 21 weeks of gestation. Nine singular pregnancies were terminated and in the twin pregnancy a selective feticide of the exencephalic co-twin was carried out. The pregnancy continued to term and a healthy newborn infant and a fetus papyraceus were born. The mummified co-twin was anencephalic and showed only the remnants of the exposed brain. Authors suggest that, as in experiments with animals, the exencephaly in humans, by the degeneration of the exposed neural tissue converts to anencephaly and in this process the macrophages in fetal circulation and in the amniotic fluid may play a significant role. The large number of these actively phagocytic macrophages can be demonstrated in the amniotic fluid samples from exencephalic fetuses.

Amniotic Fluid↗