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Biomedical subjects

W Baumgartner

Publications and source records attributed to W Baumgartner.

At least 19 recordsLinked to original sources
PubMed2001

High-gradient millimeter-wave accelerator on a planar dielectric substrate.

We report the first high-gradient studies of a millimeter-wave accelerator, employing for the first time a planar dielectric accelerator, powered by means of a 0.5-A, 300-MeV, 11.424-GHz drive electron beam, synchronous at the 8th harmonic, 91.392 GHz. Embedded in a ring-resonator circuit within the electron beam line vacuum, this structure was operated at 20 MeV/m, with a circulating power of 200 kW, for 2 x 10(5) pulses, with no sign of breakdown, dielectric charging, or other deleterious high-gradient phenomena. We also present the first measurement of the quadrupolar content of an accelerating mode.

Journal Article↗
PubMed2001

Ultrasonography of the teat canal in cows and sheep.

When the isolated teat of a cow was examined with an 8.5 MHz linear array transducer in a vertical plane, the teat canal appeared as a thin, white line, bordered on each side by parallel, thick, grey-black bands. In a horizontal plane a comparable image was obtained. In a sheep, images of comparable quality were obtained with a 12 MHz transducer. Histological studies of the tissues whose removal led to the disappearance of this characteristic ultrasonographic appearance showed that it was associated with the stratified keratinised squamous epithelium with distinct papillae. The content of keratin in the stratum corneum was apparently responsible for the bright zone; the stratum lucidum was not visible, and the surrounding dark, less echoic area was associated with the stratum granulosum. Doppler echography in live animals confirmed this designation. The outer layers of the teat wall were more echogenic.

Animals↗
PubMed2001

Total and organic mercury in the Black Sea harbour porpoise Phocoena phocoena relicta.

This paper reports on mercury (Hg) concentrations in different tissues (liver, muscle, kidney, blubber and brain) of harbour porpoises Phocoena phocoena found dead in the Black Sea between 1997 and 1999, mainly bycaught in fishing nets (n = 79). Total Hg and organic Hg (MeHg) were determined. The main factor affecting Hg accumulation was, as expected, age, with MeHg concentration increasing with age. Accumulation of high concentrations of inorganic Hg in the liver was probably due to a slow demethylation process implying the formation of tiemannite (HgSe). In older adults, liver concentrations reached 35 microg g(-1) dry weight ('ppm') total Hg and 3 microg g(-1) dw MeHg. A geographical comparison with existing data from other regions showed a generally low Hg contamination of Black Sea porpoises, one order of magnitude lower than, e.g. in the North Sea.

Adipose Tissue↗
PubMed2001

[Comparison of iodinated and barium-containing contrast media of different viscosity in the detection of pharyngeal perforation].

PURPOSE: In contrast to esophageal perforations, the more radiopaque barium-suspensions are not as important as iodinated aqueous contrast agents for the detection of pharyngeal perforations. This study was performed to find out whether the highly different viscosities (of iodinated and barium-containing contrast agents with comparable radiopacities) are a reason for this. METHODS: Viscosity, subjective difference in contrast, and CT-density of an iodinated aqueous (Telebrix) and a 50 wt/vol% barium-containing contrast agent (Micropaque) were determined. Moreover, to exclude postoperative perforation, 104 patients were prospectively examined by pharyngography using both contrast media. Pharyngographies of patients with perforation were later compared by two independent readers. All patients with perforation were followed up clinically to exclude complications due to barium administration. RESULTS: In-vitro comparison showed comparable radiopacity but the 50 wt/vol% barium-suspension was much more viscous than the iodinated contrast agent. During pharyngography, totally, 14 perforations were clearly delineated with the iodinated aqueous contrast agent. However, two of them were not detected with the barium-suspension. All the other perforations presented equally. CONCLUSIONS: Given a sufficient radiopacity, a low viscosity appears to be essential for a contrast agent to detect especially pharyngeal perforations. Thus, we recommend the sole use of an iodinated contrast agent (at suspicion of aspiration as isoosmolar variant) for this purpose.

Adult↗
PubMed2001

Perimodiolar electrodes in cochlear implant surgery.

Perimodiolar-positioned cochlear implant electrodes have been developed in order to bring the electrode contacts as close as possible to the spiral ganglion cells, which are the target of electrostimulation. This results in lower electrical thresholds, higher dynamic ranges and less channel interaction when compared with normal implant electrodes which are usually located peripherally within the scala tympani. In this study we evaluated 4 different types of perimodiolar electrode: the Clarion Preformed electrode, the Clarion Preformed electrode with positioner, the Nucleus Contour electrode and the Med-El Perimodiolar Combi 40 electrode. These devices require different approaches to achieve a perimodiolar electrode position. The electrodes were inserted in fresh human temporal bones. After processing these bones with the electrodes in situ by employing a sawing, grinding and polishing technique, the inner ear structures as well as the electrode positions could be evaluated in detail. All electrode types studied had a more or less perimodiolar position; however, each type produced a certain amount of trauma to cochlear structures which is discussed in relation to mechanical properties. Further human temporal bone studies with improved perimodiolar cochlear implant electrodes are necessary in order to find an optimized type of electrode.

Cochlea↗
PubMed2001

In vitro efficacy of chemotherapeutics as determined by 50% inhibitory concentrations in cell cultures of mammary gland tumors obtained from dogs.

OBJECTIVE: To determine the 50% inhibitory concentration (IC-50) of carboplatin, cisplatin, and doxorubicin in cell cultures of mammary gland tumors obtained from dogs and to assess whether in vitro efficacy was within the range of clinically relevant concentrations, SAMPLE POPULATION: 30 mammary gland tumors excised from dogs. PROCEDURE: Cell cultures were established from the 30 tumors. Cultures then were treated with carboplatin, cisplatin, or doxorubicin. Growth inhibition of cultures was assessed via DNA measurement 24, 48, and 72 hours after treatment. The IC-50 values were calculated by use of linear interpolation. RESULTS: Cultures varied in their pattern of susceptibility. Doxorubicin induced significantly lower IC-50 values than the platinum derivatives. Cisplatin and carboplatin had comparable effects. The IC-50 values for carboplatin and doxorubicin were in the range of clinically relevant concentrations, but only part of the cisplatin cultures had IC-50 values within clinically relevant concentrations. We did not detect differences in the in vitro susceptibility among subtypes of tumors (ie, adenocarcinoma, solid carcinoma, malignant mixed tumor). CONCLUSION AND CLINICAL RELEVANCE: The IC-50 values determined in this study allowed assessment of in vitro drug efficacy of chemotherapeutics in cultures of mammary gland tumors obtained from dogs. Variations in susceptibility were evident and emphasize the importance of assessing susceptibility and resistance patterns for each tumor. Prospective studies to assess direct correlations between in vitro and in vivo efficacy must be performed to determine the clinical predictive value of this in vitro chemosensitivity assay for treatment of dogs with mammary gland tumors.

Adenocarcinoma↗
PubMed2001

Radical cavities and cochlear implantation.

Profoundly deaf patients with chronic suppurative otitis media have been contraindicated for cochlear implantation in the past. Complications such as infection of the radical cavity, fat necrosis, skin flap problems, change in electrode position and cholesteatoma have occurred in subjects with radical cavities. The aim is to create a dry, self-cleansing, infection-free cavity. This is essential in patients about to receive a cochlear implant, as infection may be introduced into the cochlea at the implantation site and destroy any remaining neural elements. The aim of this paper was to show that it is possible to obliterate the radical cavity and perform cochlear implantation using a one-step surgical technique. Eight patients suffering from long-term bilateral chronic middle ear diseases with chronic sepsis leading to severe hearing impairment underwent cochlear implant surgery. No major complications were observed in these subjects.

Adult↗
PubMed2000

Mycobacterium avium subsp. paratuberculosis infection in cattle in Austria, diagnosis with culture, PCR and ELISA.

Serum samples from healthy, infected (n=11) and diseased (n=2) cattle as well as positive (n=17) and negative (n=41) reference sera were tested for antibodies to Mycobacterium avium subsp. paratuberculosis with two ELISA-methods (A-ELISA, Allied Monitors, Fayette, USA; H-ELISA, Institute of Microbiology and Animal Diseases, Veterinary University Hannover). Fecal samples of these animals were examined by PCR and culture. Also field serum samples found to be positive (n=664) or inconclusive (n=1589) by A-ELISA during a survey done on 11028 cattle of 2757 farms at different districts in Austria were retested with H-ELISA (Gasteiner et al., 1999). In both ELISA-methods total agreement between antibody detection and shedding of M. avium subsp. paratuberculosis (PCR, culture) in cases of diseased animals during the testing period was found. In subclinically infected animals H-ELISA showed a better correlation with the results of PCR and fecal culture. Reference serum samples of culturally negative cattle were negative in 98% by H-ELISA and in 82% by A-ELISA, and those of positive animals were positive in 59% by H-ELISA and in 82% by A-ELISA. The 664 A-ELISA positive field serum samples were positive in 20.5%, inconclusive in 32.5% and negative in 47% by H-ELISA. A-ELISA inconclusive sera gave positive reactions by H-ELISA in 5.2%, negative in 74.8% and inconclusive results in 20%. The highest prevalence of antibodies (7.9% by A- and 2.2% by H-ELISA) against M. avium subsp. paratuberculosis were found in cattle at the age of six and seven years. Seropositive animals were found at all tested ages. The A-ELISA gave two to three times more positive reactors than the H-ELISA. Also both tests showed the highest prevalence of reagents among Holstein Friesian (6.2% by A-ELISA, 2.5% by H-ELISA) followed by other cattle breeds. Seropositive cattle were observed in all districts of Austria in 3. 3-7.1% and in 0.5-1.8% of herds according to A- and H-ELISA, respectively.

Animals↗
PubMed2000

Cadherin interaction probed by atomic force microscopy.

Single molecule atomic force microscopy was used to characterize structure, binding strength (unbinding force), and binding kinetics of a classical cadherin, vascular endothelial (VE)-cadherin, secreted by transfected Chinese hamster ovary cells as cis-dimerized full-length external domain fused to Fc-portion of human IgG. In physiological buffer, the external domain of VE-cadherin dimers is a approximately 20-nm-long rod-shaped molecule that collapses and dissociates into monomers (V-shaped structures) in the absence of Ca(2+). Trans-interaction of dimers is a low-affinity reaction (K(D) = 10(-3)-10(-5) M, k(off) = 1.8 s(-1), k(on) = 10(3)-10(5) M(-1) x s(-1)) with relatively low unbinding force (35-55 pN at retrace velocities of 200-4,000 nm x s(-1)). Higher order unbinding forces, that increase with interaction time, indicate association of cadherins into complexes with cumulative binding strength. These observations favor a model by which the inherently weak unit binding strength and affinity of cadherin trans-interaction requires clustering and cytoskeletal immobilization for amplification. Binding is regulated by low-affinity Ca(2+) binding sites (K(D) = 1.15 mM) with high cooperativity (Hill coefficient of 5.04). Local changes of free extracellular Ca(2+) in the narrow intercellular space may be of physiological importance to facilitate rapid remodeling of intercellular adhesion and communication.

Animals↗
PubMed2000

Steady-state gel electrophoresis of long polymer molecules: a theoretical study.

The velocity of long polymer molecules in a gel and the liquid flow profile in the vicinity of a molecule's surface were studied theoretically by combining the Navier-Stokes equation with the Poisson-Boltzmann equation. The electrophoretic mobility has been calculated in dependence of the ionic strength of the electrolyte solution, its viscosity, the gels' volume friction coefficient, the surface charge and the radius of the polymer molecule. The results are presented in a nondimensional form and depend on two dimensionless parameters only. The first parameter is the radius of the polymer molecule in units of the Debye length. The second is a parameter comprising the electrolyte's viscosity and the gel density. Thus, by similarity theory, the results apply to any given experimental arrangement.

Biophysics↗
PubMed2000

Data analysis of interaction forces measured with the atomic force microscope

The force-distance cycle mode of the atomic force microscope (AFM) allows for detection of interaction forces between the AFM-tip and a substrate (probe). This can either be a direct tip-sample interaction or an interaction between molecules coupled to the tip and probe, respectively. The interaction forces are typically in the range of a few pN to some hundred pN. In this article we describe algorithms for the analysis of force-distance cycles, to quantify interaction forces between tip and probe. Both, the direct tip-probe interaction as well as the interaction between specifically bound molecules are analyzed. The molecules bound to tip and probe have to be either long and flexible or have to be bound via a flexible cross linker. The algorithms are exemplified on direct tip-probe interactions and on unbinding events of cadherins which are bound via PEG-spacers to the AFM-tip and to the probe.

Journal Article↗
PubMed2000

[Effect of mycotoxin contaminated feed on production parameters of dairy cows].

Based on a feeding trial using 27 lactating "Simmental-cows" the effect of naturally contaminated feed with deoxynivalenol (DON) as well as zearalenone (ZON) regarding production parameters was examined. 3 groups of cows according to lactation number, milk yield (kg ECM) and body mass were used. The average daily intake of DON in group K was 12.4 mg, in group T 14.1 mg and in group M 14.3 mg and ZON in group K was 12.4 mg, in group T 0.67 mg and in group M 0.68 mg respectively. The feed of animals of group M was supplemented with "Mycofix Plus" as mycotoxin inactivator. The red and white blood picture including the thrombocytes were in all groups within the normal range. Concerning enzymes (GGT, AP) and metabolites (GLUC, TBIL, UREA, CREA) the mean values of the 3 groups were in the normal range. Slightly increased were the mean values of all groups in respect to the AST- and GLDH-activities. Volatile fatty acids of the rumen content were significantly highest in group M, also the number of dead rumen infusoria was significantly decreased, but the counts of small sized infusoria increased. The study has shown that "Mycofix Plus" might be able to enhance the activity of rumen flora concerning detoxification of mycotoxins in feed of dairy cows.

Animals↗
PubMed1999

[Malignant tumors of the mouth cavity and oropharynx. Stage classification].

Staging of malignant tumours of the oral cavity and the oropharynx not only requires far more than a basic knowledge of anatomy and the usual pathways of spread, but also a broad understanding of the diagnostic benefits of current imaging modalities. As radiology should never try to replace histology, the main aim should be precise prediction of tumour margins and differentiation of tumour from edema and posttherapeutic changes. Only then will imaging studies have a significant clinical impact.

Carcinoma, Squamous Cell↗
PubMed1999

Patient preferences in coronary revascularization.

BACKGROUND: This study was performed to assess patient preferences for consequences of 3 coronary revascularization procedures: angioplasty, conventional coronary bypass surgery, and minimally invasive coronary bypass surgery. METHOD: A nationwide sample of 3 types of respondents was recruited: respondents with no heart disease (n = 89), respondents with heart disease who had not undergone cardiac surgery (n = 97), and respondents with heart disease who had undergone cardiac surgery (n = 118). RESULTS: Sixty-two percent ranked the risk of repeat revascularization as the most important concern, followed by postprocedure pain (22%), time to recovery of physical functioning (8%), time in hospital (4%), and body appearance (4%). Respondents preferred angioplasty to conventional and minimally invasive cardiac surgery if the 3-year risk of repeat revascularization with angioplasty were to decline to less than 28% and 21%, respectively. CONCLUSION: These data suggest that patient preference should influence individual and policy recommendations when choosing among coronary revascularization procedures.

Data Collection↗
PubMed1999

Two-microelectrode voltage clamp of Xenopus oocytes: voltage errors and compensation for local current flow.

Oocytes from Xenopus laevis are commonly used as an expression system for ion channel proteins. The most common method for their electrophysiological investigation is the two-microelectrode voltage clamp technique. The quality of voltage clamp recordings obtained with this technique is poor when membrane currents are large and when rapid charging of the membrane is desired. Detailed mathematical modeling of the experimental setup shows that the reasons for this weak performance are the electrical properties of the oocytes and the geometry of the setup. We measured the cytosolic conductivity to be approximately 5 times lower than that of the typical bath solution, and the specific membrane capacitance to be approximately 6 times higher than that of a simple lipid bilayer. The diameter of oocytes is typically approximately 1 mm, whereas the penetration depth of the microelectrodes is limited to approximately 100 microm. This eccentric current injection, in combination with the large time constants caused by the low conductivity and the high capacitance, yields large deviations from isopotentiality that decay slowly with time constants of up to 150 micros. The inhomogeneity of the membrane potential can be greatly reduced by introducing an additional, extracellular current-passing electrode. The geometrical and electrical parameters of the setup are optimized and initial experiments show that this method should allow for faster and more uniform control of membrane potential.

Animals↗
PubMed1999

Serological cross-sectional study of paratuberculosis in cattle in Austria.

From 1995 to 1997, the prevalence of serum antibodies against Mycobacterium avium subspecies paratuberculosis (M. av. ssp. ptbc.)--the causal agent of paratuberculosis (Johne's Disease)--was examined in 11,028 Austrian cattle. Samples from the four oldest cattle on 2757 farms were collected according to a specific sampling schedule for this epidemiological study. District, age and breed of animals were included as variables in this study. For antibody screening against M. avium subspecies paratuberculosis, a modified, commercially available ELISA (ALLIED Monitors, Fayette, USA) was employed. A total of 2253 samples that were found to be positive or questionable were subjected to further testing with a more specific ELISA (Institute of Microbiology and Infectious Animal Diseases). Results of this study were used for statistical analysis. The average prevalence of antibodies to M. avium subspecies paratuberculosis was 1.99% in Austria. The highest prevalence was seen in 6-year-old cattle (2.84%) and Holstein Frisian cattle (3.51%). Sero-positive animals were found on 6.96% of farms tested, and the prevalence was highest in Vorarlberg, followed by Salzburg, the Tyrol, Styria and Carinthia. This study is unique in Europe in the use of an adequate random sampling plan for an investigation of this magnitude.

Age Factors↗
PubMed1999

Intracochlear position of cochlear implant electrodes.

There are many different types of cochlear implants available on the market today and they are constantly being re-evaluated and changed. Knowledge of the exact position of the electrode within the cochlea is important in order to improve the electrical stimulation of the hearing nerve by the implants. The stimulating electrodes are usually located peripherally within the scala tympani, although several attempts have been made to develop peri-modiolar located electrode arrays. In this study, our goal was to evaluate the intracochlear positions of Nucleus, Combi 40/Combi 40 +, and newly developed peri-modiolar positioned electrodes by inserting them into fresh human temporal bones. After insertion, the bones were then histologically processed with the electrodes in situ, following perilymphatic formalin perfusion and methylmethacrylate embedding. Sections of the bones 80-100 microm thick were prepared using a sawing, grinding and polishing technique. This technique resulted in excellent preservation of the inner ear structures and clear identification of each electrode. The different types of electrodes were then evaluated as to their insertion depth, trauma to cochlear structures and location in relation to the scala tympani walls.

Cadaver↗