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Biomedical subjects

A Schenk

Publications and source records attributed to A Schenk.

At least 19 recordsLinked to original sources
PubMed2007

Preoperative volume prediction in adult living donor liver transplantation: how much can we rely on it?

Accurate preoperative prediction of functional donor and remnant hemiliver volumes in live donor liver transplantation is essential in preventing postoperative liver failure and optimizing safety. Our aim was (1) to evaluate volume variability associated with multiphasic CT imaging and (2) to determine over- or under-estimations of 3-D CT graft-volume assessments based on 'largest' versus 'smallest' CT phases with respect to intraoperative findings. Native, arterial and venous phase CT images from 83 potential live liver donors were subject to 3-D CT liver volume calculations and virtual 3-D liver partitioning. Estimates were compared to intraoperative volumes obtained in 43 cases. Calculated (preoperative) graft-volume-body-weight-ratios (GVBWR) versus measured (intraoperative) graft-weight-body-weight-ratios (GWBWR) were analyzed. Significant differences in total liver volume- and in graft-liver volume calculations were found among the largest (venous) and smallest (native) CT phases. High significant overestimations were observed in graft-volume determinations and in GVBWR-calculations based on the 'largest' CT phase when compared to intraoperatively obtained graft-weight and -GWBWR values. In contrast, differences among intraoperative measurements and preoperative calculations based on the 'smallest' CT phase yielded less significant overestimations. While 3-D CT volumetry based on the 'largest' (venous) CT phase is associated with considerable overestimation, 3-D volumetry based on the 'smallest' (native) CT phase accurately matches the intraoperative findings.

Donor Selection↗
PubMed2006

The "territorial belonging" of the middle hepatic vein: a troublesome dilemma in adult live donor liver transplantation--anatomical evidence based on virtual 3-dimensional-computed tomography-imaging reconstructions.

BACKGROUND: The venous drainage of the liver plays an essential role in securing viability of both graft and remnant in live donor liver transplantation (LDLT). There is still controversy on whether the middle hepatic vein (MHV) should be routinely included as part of the graft or retained with the remnant liver. The purpose of this study was to analyze hepatic venous drainage patterns based on information obtained by 3-dimensional CT-imaging reconstructions. METHODOLOGY: Fifty five potential live liver donors were evaluated between January 2003 and May 2004 at our Institution. We analyzed two anatomical definitions of liver dominance: total liver dominance (TLD) and hemiliver dominance (HLD). The following concepts were addressed: 1) Hepatic vein territories, 2) Hepatic vein dominance relationship, 3) Territorial belonging- patterns of the MHV to the right and left hemilivers, additionally an analysis of venous outflow in the central liver sectors was performed. RESULTS: Our results showed that: 1) The definitions of dominance: TLD vs. HLD overlap, displaying the MHV belonging, by taking into account the individual right hepatic vein (RHV) variability; 2) A dominant RHV for the whole liver indicates that the RHV is also dominant in the right hemiliver; 3) The MHV belongs predominantly to the left hemiliver (LHL); 4) The left hepatic vein (LHV) is dominant in the LHL. CONCLUSION: Both dominance definitions provide independent mappings of the liver and offer helpful insight into venous dominance relationship.

Adult↗
PubMed2006

[Computer-assisted planning in living donor liver operation].

INTRODUCTION: The appropriate recipient/donor match is a prerequisite for successful living donor liver transplantation (LDLT). A precise knowledge of the liver anatomy and the functional liver volume plays a key role in allocating live liver donor candidates. With the new software HepaVision, we obtained information on liver mapping by means of virtual 3-dimensional non-invasive imaging reconstructions and were able to perform a virtual simulation of the liver transsection. Aim of our study was to investigate, whether this new computer technology is advantageous in surgery planning for LDLT. METHODS: From January 2002 until December 2004 355 liver transplantations were performed in our department, of which 36 were LDLT. According to our evaluation protocol 135 potential donors (63 male, 72 female) between 18 to 59 years received preoperatively an all-in-one CT. The acquired data sets were further analysed with the software HepaVision (MeVis, Germany). RESULTS: Of the 135 evaluated donors, we excluded 99 (73 %) from donation based on the HepaVision-data. Reason for exclusion was an inadequate liver volume (70.8 %) or a risk related anatomical anomaly (2.2 %). In the remaining 36 cases a successful graft donation was possible. There were no postoperative complications in the donors and recipients, directly related to a misjudgment of the anatomy or miscalculation of the liver volume. CONCLUSION: The systematic use of HepaVision for surgery planning proved to be indispensable for proper donor selection. A virtual simulation of the liver transsection on 3D-model additionally increased the safety of the operation, consequently decreasing the risk for the donor.

Adolescent↗
PubMed2005

Anatomical and physiological classification of hepatic vein dominance applied to liver transplantation.

BACKGROUND: Proper outflow reconstruction is essential in LDLT. Preoperative planning requires meticulous attention to hepatic vein dominance patterns. The purpose of our study was to provide a combined anatomical-physiological classification of hepatic vein dominance useful for surgical decision-making in both donors and recipients. METHODOLOGY: We analyzed 3-dimensional CT-imaging reconstructions of 55 potential live liver donors evaluated at our Institution between January 2003 and May 2004. RESULTS: Our data revealed that: 1) The middle hepatic vein (MHV) and left hepatic vein (LHV) show a relative lack of anatomical diversity, whereas the right hepatic vein (RHV) exhibits multiple variants, 2) 45% donors had inferior hepatic veins (IHV) with anatomically and physiologically relevant venous drainage territories, 3) The RHV is usually dominant when present as a single vein without anatomical IHV (type 1A), or when considered as a complex with IHV (type 1Bx) (80% vs. 88%), 4) Only 55% of dominant type 1Bx RHV/IHV-complex automatically included a dominant type 1By RHV by itself, 5) A single RHV out of anatomical complex with IHV (type 1By) was dominant in only 48% of our donor candidates, 6) The MHV types 2A and 2By are strongly dominant accounting for up to 57% of total liver volume (TLV). CONCLUSIONS: We propose a new classification based on both anatomical and physiological hepatic venous configurations. Our model also provides a new nomenclature that can be universally applied to preoperative planning in LDLT.

Adolescent↗
PubMed2005

Electrochemical characterisation of dental alloys: its possibilities and limitations.

Dental alloys are metallic biomaterials which have a broad variation of composition compared to technical alloys. It is therefore in the interest of patients and technicians to conduct a good assessment of the electrochemical behaviour of dental alloys in order to collect information about their corrosion resistance. The purpose of this work was to demonstrate possibilities and limitations of two electrochemical techniques: the voltammetry of immobilised microparticles (ViMP) onto lead, and cyclic voltammetry measurements with the help of the mini-cell system (MCS). Based on fingerprints obtained from ViMP it was possible to analyse and differentiate the dental alloys. The results obtained by MCS were comparable with ViMP, but give a better understanding of the corrosion behaviour of the materials.

Copper↗
PubMed2004

[Evaluation of a new software tool for the automatic volume calculation of hepatic tumors. First results].

PURPOSE: Computed tomography has become the preferred method in detecting liver carcinomas. The introduction of spiral CT added volumetric assessment of intrahepatic tumors, which was unattainable in the clinical routine with incremental CT due to complex planimetric revisions and excessive computing time. In an ongoing clinical study, a new software tool was tested for the automatic detection of tumor volume and the time needed for this procedure. MATERIALS AND METHODS: We analyzed patients suffering from hepatocellular carcinoma (HCC). All patients underwent treatment with repeated transcatheter chemoembolization of the hepatic arteria. The volumes of the HCC lesions detected in CT were measured with the new software tool in HepaVison (MeVis, Germany). The results were compared with manual planimetric calculation of the volume performed by three independent radiologists. RESULTS: Our first results in 16 patients show a correlation between the automatically and the manually calculated volumes (up to a difference of 2 ml) of 96.8 %. While the manual method of analyzing the volume of a lesion requires 2.5 minutes on average, the automatic method merely requires about 30 seconds of user interaction time. CONCLUSION: These preliminary results show a good correlation between automatic and manual calculations of the tumor volume. The new software tool requires less time for accurate determination of the tumor volume and can be applied in the daily clinical routine.

Algorithms↗
PubMed2003

Membrane protein reconstitution and crystallization by controlled dilution.

Efficient reconstitution of membrane proteins for functional analyses can be achieved by dilution of a ternary mixture containing proteins, lipids and detergents. Once the dilution reaches the point where the free detergent concentration would become lower than the critical micellar concentration, detergent is recruited from the bound detergent pool, and association of proteins and lipids is initiated. Here we show that dilution is also suitable for the assembly of two-dimensional crystals. A device has been designed that allows controlled dilution of a protein-lipid-detergent mixture to induce formation of densely packed or crystalline proteoliposomes. Turbidity is used to monitor the progress of reconstitution on-line, while dilution is achieved by computer-controlled addition of buffer solution in sub-microliter steps. This system has mainly been tested with porin OmpF, a typical beta-barrel protein, and aquaporin-1, a typical alpha-helical protein. The results demonstrate that large, highly ordered two-dimensional crystals can be produced by the dilution method.

Aquaporin 1↗
PubMed2002

Using survival analysis to investigate the effect of UV-C and heat treatment on storage rot of strawberry and sweet cherry.

Ultraviolet light and heat treatment are proposed as alternative techniques for the use of chemicals to reduce the development of the spoilage fungi Botrytis cinerea and Monilinia fructigena on strawberry and sweet cherry, respectively, during storage. In order to investigate the effect of both physical techniques on microbial inactivation and on fruit quality, inoculated berries were subjected to different temperatures (40-48 degrees C) and UV-C doses (0.05-1.50 J/cm2). For each condition, 20 berries were used. After the treatment, fungal growth, visual damage (holes, stains) and fruit firmness were evaluated during a period of 10 days. The experimental data were analysed statistically using survival analysis techniques. Fungal growth on strawberries was significantly retarded using UV-C doses of 0.05 J/cm2 and higher. The same treatment had no significant effect when applied to cherries. The highest doses (1.00 and 1.50 J/cm2) had a negative effect on the calyx of the strawberry, causing browning and drying of the leaves. No beneficial effect of a low temperature treatment (40-48 degrees C) on the shelf life of strawberries was observed, but fungal development on cherries was retarded at temperatures of 45 and 48 degrees C. These temperatures caused severe damage on strawberries (soft stains, holes, decreased firmness), but had no influence on the quality of sweet cherries.

Ascomycota↗
PubMed2001

Thermoregulated expression of virulence factors in plant-associated bacteria.

Pathogenic bacteria with habitats inside and outside a given host react to changes in environmental parameters by synthesizing gene products specifically needed during pathogenic or saprophytic growth. Temperature effects have been investigated in detail for pathogens of warm-blooded hosts, and major principles governing the temperature-sensing mechanism have been uncovered. Generally, transcription of virulence genes in these pathogens is induced at higher temperatures (37-41 degrees C), which are typical for body cavities and host tissues. However, effects of temperature on virulence determinants in plant pathogenic bacteria have not been focused on in detail. Interestingly, almost all virulence genes of plant pathogenic bacteria studied with respect to temperature exhibit increased transcription at temperatures well below the respective growth optima. This includes virulence determinants such as those directing bacteria-to-plant gene transfer, plant cell-wall-degrading enzymes, phytotoxins, ice nucleation activity, exopolysaccharide production, and the type III protein secretion machinery. Although many of the studied phytopathogens cause "cold-weather" diseases, the ecological rationale for this phenomenon remains to be studied in detail. This mini-review summarizes our current knowledge on thermoregulation of cellular processes taking place in bacterial phytopathogens in response to temperature changes. Since the temperature range of interest is different from that relevant to pathogens of mammals, one envisions novel principles of thermo-sensing in bacteria interacting with plants.

Bacteria↗
PubMed2001

[Acute pain therapy in the regional public hospital].

Pain therapy is an essential component of clinical care. Using the example of a regional hospital, the various possibilities of providing effective pain therapy are discussed. They range from consultations at which patients are given information about their forthcoming anaesthetic to the work done in the recovery room, the surgical departments, the intensive care unit, the delivery room and the emergency department. Taking centre stage among the proven therapies are bolus injections of opiates, continuous infusion of analgetics and pain therapy with patient-controlled pumps or spinal catheters. Proven methods of organising acute pain service are also discussed. The most decisive factor is the degree of patient satisfaction, which can be ensured by measures of quality control.

Analgesics↗
PubMed2000

Sensitivity enhancement in fluorescence correlation spectroscopy of multiple species using time-gated detection.

Fluorescence correlation spectroscopy (FCS) is a powerful technique to measure chemical reaction rates and diffusion coefficients of molecules in thermal equilibrium. The capabilities of FCS can be enhanced by measuring the energy, polarization, or delay time between absorption and emission of the collected fluorescence photons in addition to their arrival times. This information can be used to change the relative intensities of multiple fluorescent species in FCS measurements and, thus, the amplitude of the intensity autocorrelation function. Here we demonstrate this strategy using lifetime gating in FCS experiments. Using pulsed laser excitation and laser-synchronized gating in the detection channel, we suppress photons emitted within a certain time interval after excitation. Three applications of the gating technique are presented: suppression of background fluorescence, simplification of FCS reaction studies, and investigation of lifetime heterogeneity of fluorescently labeled biomolecules. The usefulness of this technique for measuring forward and backward rates of protein fluctuations in equilibrium and for distinguishing between static and dynamic heterogeneity makes it a promising tool in the investigation of chemical reactions and conformational fluctuations in biomolecules.

Diffusion↗
PubMed1998

Pseudotype formation of Moloney murine leukemia virus with Sendai virus glycoprotein F.

Mixed infection of cells with both Moloney murine leukemia virus (MoMLV) and related or heterologous viruses produces progeny pseudotype virions bearing the MoMLV genome encapsulated by the envelope of the other virus. In this study, pseudotype formation between MoMLV and the prototype parainfluenza virus Sendai virus (SV) was investigated. We report for the first time that SV infection of MoMLV producer cells results in the formation of MoMLV(SV) pseudotypes, which display a largely extended host range compared to that of MoMLV particles. This could be associated with SV hemagglutinin-neuraminidase (SV-HN) glycoprotein incorporation into MoMLV envelopes. In contrast, solitary incorporation of the other SV glycoprotein, SV fusion protein (SV-F), resulted in a distinct and narrow extension of the MoMLV host range to asialoglycoprotein receptor (ASGP-R)-positive cells (e.g., cultured human hepatoma cells). Since stably ASGP-R cDNA-transfected MDCK cells, but not parental ASGP-R-negative MDCK cells, were found to be transduced by MoMLV(SV-F) pseudotypes and transduction of ASGP-R-expressing cells was found to be inhibited by ASGP-R antiserum, a direct proof for the ASGP-R-restricted tropism of MoMLV(SV-F) pseudotypes was provided. Cultivation of ASGP-R-positive HepG2 hepatoma cells on Transwell-COL membranes led to a significant enhancement of MoMLV(SV-F) titers in subsequent flowthrough transduction experiments, thereby suggesting the importance of ASGP-R accessibility at the basolateral domain for MoMLV(SV-F) pseudotype transduction. The availability of such ASGP-R-restricted MoMLV(SV-F)-pseudotyped vectors opens up new perspectives for future liver-restricted therapeutic gene transfer applications.

Animals↗
PubMed1996

What we have learned about bumetanide and the concept of multispecific bile acid/drug transporters from the liver.

Bumetanide is a weak organic acid which is transported into hepatocytes by a transport system that is related neither to the cloned sodium-dependent taurocholate cotransporting polypeptide Ntcp nor to the cloned organic anion transporting polypeptide oatp. Bumetanide is known to be transported in the kidney by a multispecific organic anion transporter which is the pAH-transporter from the proximal tubule cell. In the liver, bumetanide uptake competes with bile acid uptake, indicating a functionally related multispecific transporter for bile acids and drugs in hepatocytes. This multispecific bile acid transporter MBAT has not been cloned yet. When basolateral membranes were photoaffinity labeled with [3H]bumetanide, several bumetanide binding proteins were separated and identified after protein sequencing from two-dimensional electrophoresis gels.

Adenosine Triphosphate↗
PubMed1994

Extrathymic development and function of human T-lymphocytes from bone marrow cells in vitro.

To enrich low-density human bone marrow (BM) cells for putative progenitors of T-lymphocytes, CD7+ CD3- cells were sorted (purity was estimated at > 99.9%) and cultured under limiting dilution conditions with irradiated allogeneic stimulator cells, interleukin (IL) 2, and PHA. Clonal populations were available for analysis from Day 25 onward. By this time, all clones (n = 54) expressed CD3 and alpha/beta-T cell receptor (TCR2). Fifty percent of the clones were CD4+ and 50% were CD8+, with no double positives, whereas almost all clones obtained under identical conditions from peripheral blood (PB) cells were CD4+. All clones were capable of autocrine proliferation, which was blocked by CD25 or CD71 mAb. Most or all clones tested (n = 15) responded to IL 4 and IL 7 as well as IL 2, but not to IL 3 or GM-CSF and only two responded to IL 9. Most clones accumulated mRNA for GM-CSF, IL 2, IL 3, IL 4, IL 5 and also IL 9, but 6 of 11 were negative for IFN-gamma mRNA, and all were negative for IL 6 mRNA. Sixty-two percent of CD4+ and 85% of CD8+ clones (total 70% of all clones) mediated lectin-dependent cell lysis; but whereas 35% of CD4+ and 65% of CD8+ clones (total 46% of all clones) lysed K562 natural killer (NK)-susceptible targets, only 24% of CD4+ and 5% of CD8+ clones (total 17% of all clones) killed lymphokine-activated killer (LAK)-susceptible Daudi cells. Only three clones lysed allogeneic LCL targets and none lysed autologous targets. Furthermore, none of the clones proliferated when stimulated by autologous cells, neither did they suppress proliferative responses of autologous cells. These results suggest that CD3- cells from the bone marrow can acquire functional cytotoxic and proliferative programs extrathymically during in vitro culture with IL 2, mitogens and allogeneic cells, but do not manifest autoreactivity in the three test systems, cytotoxicity, suppression, or autocrine proliferation.

Antigens, Differentiation, T-Lymphocyte↗