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Biomedical subjects

G Schweitzer

Publications and source records attributed to G Schweitzer.

At least 19 recordsLinked to original sources
PubMed1999

Virtual reality based surgery simulation for endoscopic gynaecology.

Virtual reality (VR) based surgical simulator systems offer very elegant possibilities to both enrich and enhance traditional education in endoscopic surgery. However, while a wide range of VR simulator systems have been proposed and realized in the past few years, most of these systems are far from able to provide a reasonably realistic surgical environment. We explore the basic approaches to the current limits of realism and ultimately seek to extend these based on our description and analysis of the most important components of a VR-based endoscopic simulator. The feasibility of the proposed techniques is demonstrated on a first modular prototype system implementing the basic algorithms for VR-training in gynaecologic laparoscopy.

Computer Graphics↗
PubMed1998

Behaviorally conditioned effects of Cyclosporine A on the immune system of rats: specific alterations of blood leukocyte numbers and decrease of granulocyte function.

Immunosuppression induced by Cyclosporine A (CsA) can be behaviorally conditioned. It is unknown, however, whether a taste aversion paradigm using CsA as an unconditioned stimulus (UCS) induces alterations of blood leukocyte numbers and function. Results obtained by three-colour flow cytometry and granulocyte chemiluminescence response demonstrate that in conditioned rats, absolute numbers of lymphocyte subsets, including B, CD8+ T cells and CD4+ naive and memory T cells, and granulocyte numbers and function were significantly decreased. In contrast to the conditioned response, CsA treatment alone increased lymphocyte numbers and did not affect granulocyte function. Thus, our data demonstrate that behaviorally conditioned CsA effects can be monitored in the blood. In addition, results indicate that the CNS mediates the behaviorally conditioned immunosuppression by reducing the availability and function of granulocytes and lymphocytes.

Animals↗
PubMed1997

Fluorescence spectroscopy of the longwave chlorophylls in trimeric and monomeric photosystem I core complexes from the cyanobacterium Spirulina platensis.

The organization and interaction of chlorophylls (Chl) and the kinetics of the energy transfer in the core antenna of photosystem I (PSI) trimeric and monomeric complexes, isolated from Spirulina platensis with Triton X-100 have been studied by stationary and time-resolved fluorescence. At 295 K both complexes show an unusually intense long-wavelength emission band with prominent peaks at 730 nm (trimers) or 715 nm (monomers), whose intensity is independent of the redox state of P700. A broad band extending from 710 to 740 nm in the absorption and fluorescence excitation spectra of trimers also indicates the existence of the longwave Chls at 295 K. The 77 K fluorescence emission of PSI trimers frozen after addition of dithionite under illumination (P700 and the PSI acceptor side reduced) shows an intense band at 760 (F760) and a smaller one at 725 nm (F725); when P700 is oxidized, the intensity of F760 decreases about 15 times. In the 77 K spectrum of monomers only F725 is present in the longwave region, and its intensity does not depend on the redox state of P700. Bands of Chls with maxima near 680, 710, and 738 nm were found in the 77 K excitation spectrum of trimers, and bands near 680 and 710 nm were seen in the spectrum of monomers. Five spectrally different red Chl forms in PSI trimers and three red Chl in monomers have been resolved by deconvolution of their 77 K absorption spectra. The difference absorption spectrum, trimers-minus-monomers, shows that the appearance of the 735 nm band in trimers is accompanied by a decrease of 708, 698, and 688 nm bands present in monomers. The reversible changes of F760 intensity of Spirulina membranes as a result of their salt treatment confirm the idea that the most longwave Chl form originates from an interaction of Chls bound to different monomeric PSI subunits forming the trimer. The time-resolved fluorescence spectra of PSI trimers and monomers, measured at 287 K in the region 680-770 nm, are substantially different, although a set of similar lifetimes (9, approximately 30, approximately 66, and 1400-2200 ps) was necessary for a good fit. No effect of P700 redox state was observed on the fluorescence kinetics of both complexes at 287 K.

Chlorophyll↗
PubMed1997

Endothelial-derived superoxide anions in pig coronary arteries: evidence from lucigenin chemiluminescence and histochemical techniques.

1. The generation of superoxide anions (O2-) by intact pig coronary artery rings was measured using a lucigenin-enhanced chemiluminescence technique and a histochemical technique with Nitroblue Tetrazolium (NBT) staining. 2. Isolated arteries with intact endothelium generated O2- at a rate of 9.0 +/- 0.8 pmol min-1 (mg dry weight)-1; this rate was diminished by about 24% when the endothelium was removed. The NBT staining of arterial ring preparations showed formazan precipitation mainly in the intima. Arterial rings were pretreated with diethylthiocarbamate in order to inhibit Cu-Zn superoxide dismutase (SOD) activity which increased the O2- generation by 184 +/- 55% (n = 10; P < 0.01). Stimulation of protein kinase C with phorbol 12-myristate 13-acetate (5 microM) enhanced endothelium-dependent O2- generation by 136 +/- 20% (n = 19; P < 0.01). Neither stimulation with bradykinin or substance P, nor inhibition with NG-nitro-L-arginine methyl ester of endothelial nitric oxide synthase had a significant effect on O2- generation. In contrast, the inhibition of flavoproteins with diphenyliodonium decreased concentration-dependent O2- generation (IC50, 1.85 +/- 5.33 microM). Inhibition of tetrahydrobiopterin synthesis with 2,4-diamino-6-hydroxy-pyrimidine resulted in a reduced generation of O2- by about 55%. 3. The addition of 100 microM NADH and 100 microM NADPH resulted in an excessive generation of O2- at a rate of 0.68 +/- 0.03 and 0.26 +/- 0.01 nmol O2- min-1 (mg protein)-1, respectively, in the membrane fraction, but not in the cytosolic fraction, of homogenates obtained from arteries. 4. The results suggest that intact coronary arteries do generate O2- under basal conditions and that the endothelial layer significantly contributes to this phenomenon. This generation of O2- is greatly influenced by intrinsic SOD activity. It is suggested that basal vascular O2- generation is mainly due to membrane-bound NAD(P)H oxidase activity and/or tetrahydrobiopterin-dependent processes.

Acridines↗
PubMed1995

[Effect of primary fracture management on craniocerebral trauma in polytrauma. An animal experiment study].

Severe head trauma (BI) associated with long bone fractures is present in about 60% of polytraumatized patients admitted to hospital. However, there is no consensus regarding early fracture stabilization in such patients. In an experimental sheep study, the influence of intramedullary nailing of the femur (IMNF) on a cold-induced, vasogenic brain edema (method of Klatzo) in combination with traumatic hemorrhagic shock (THS) was investigated. Three animal groups (n = 6) were explored: group A, only BI; group B, BI and THS; group C, BI, THS and IMNF. The animals remained intubated, on controlled ventilation, sedated and received analgesia during the whole experiment. For a period of 6 h after the cold-induced brain injury the hemodynamic changes were measured and the intracranial pressure (ICP) was recorded in the left and the right hemisphere continuously. The hemorrhagic shock (MAP = 60 mm Hg) was maintained over 1.5 h. At the end of the reperfusion period (2 h) the nailing of the femur was performed. The animals were killed and the percentage water content of the brain was determined and compared with the brain water content of a control group (n = 6). There were no significant differences in ICP between groups A, B and C before or after IMNF, but in group C the ICP increased significantly after nailing. Brain water content in group C was significantly higher than in the control group and slightly significantly higher than in groups A and B. Brain edema and ICP are increased by IMNF.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Ascorbic acid reduces the endotoxin-induced lung injury in awake sheep.

Our aim was to investigate whether ascorbic acid can reduce reactive oxygen metabolite-mediated acute lung injury. The effects of intravenous administration of Escherichia coli endotoxin were studied, with and without ascorbic acid infusion, on haemodynamics, lung lymph flow, cardio-respiratory and neutrophil function in chronically instrumented sheep. Paired experiments were performed on eight sheep in which they received either endotoxin alone (0.5 micrograms kg-1 b.w.) (ET group) or in combination with an ascorbic acid infusion (1 g kg-1 b.w. bolus injection followed by 0.2 g kg-1 h-1 continuous infusion) ET + ASC group) in random order. Four of the animals also received ascorbic acid alone (ASC group). As a result, for the ET + ASC group a general and mostly significant improvement (P < 0.05) in the early hypertensive phase (0-60 min, P values) and in the late permeability phase (2-4 h, *P values) of cardiorespiratory function (mean artery pressure: P/*P = 0.283/0.049; mean pulmonary artery pressure: P/*P = 0.0001/0.0001; mean pulmonary artery wedge pressure: P/*P = 0.012/0.001; right ventricular stroke work index: P/*P = 0.02/0.0001; cardiac index: P/*P = 0.797/0.755; arterial oxygen saturation: P/*P = 0.0059/0.01; arterial-venous difference of oxygen tension: P/*P = 0.011/0.0005), oxygen consumption: P/*P = 0.013/0.035, lung lymph flow: P/*P = 0.562/0.012, lymph/plasma protein ratio: P/*P = 0.304/0.008 and protein clearance: P/*P = 0.56/0.05 was observed in comparison with the ET group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Influences of different methods of intramedullary femoral nailing on lung function in patients with multiple trauma.

We investigated the effects of primary (< or = 24 h) intramedullary femoral nailing on lung function and pulmonary hemodynamics in patients with multiple trauma. Two groups were separated: the group with primary femoral nailing with reaming (group RFN) was submitted to femoral nailing after reaming of the medullary canal; in the group with unreamed femoral nailing (group UFN) a small-diameter solid nail was inserted without reaming. Lung function was assessed by oxygenation ratio (PaO2/FIO2), and pulmonary hemodynamics by intraoperative pulmonary artery catheter measurements. Central venous blood concentrations of elastase and the platelet count were determined during and 3 days after surgery. Lung function was stable in UFN patients (n = 14), but deteriorated in RFN patients (n = 17) from 353 +/- 24 (PaO2/FIO2 preoperatively) to 260 +/- 28 (PaO2/FIO2 postoperatively) (p < 0.05) and improved only after 48 hours. Pulmonary artery pressure (PAP) did not change during surgery in UFN patients; in RFN patients PAP increased from 27.2 +/- 3.1 mm Hg (preoperatively) to 36.3 +/- 4.1 mm Hg (p < 0.05) upon reaming and normalized 1 hour after insertion of the nail. Femoral nailing after reaming represents a potential risk with respect to lung function disturbances. This might trigger the development of adult respiratory distress syndrome (ARDS), especially in patients at extra risk of this complication (additional lung contusion, "borderline patient"). In these cases unreamed femoral nailing might offer an alternative by allowing primary intramedullary stabilization without the risk of adverse effects to the lung.

Adult↗
PubMed1992

Pulmonary damage after intramedullary femoral nailing in traumatized sheep--is there an effect from different nailing methods?

Stabilization of femoral shaft fractures is a controversial issue in the management of patients with multiple trauma. Intramedullary nailing usually is preferred primarily; in recent years, however, pulmonary complications (e.g., ARDS) have been reported that were attributed to the reaming procedure. To study the effects of different nailing methods in a model of severe trauma, hemorrhagic shock and lung contusion were created at day 1 in sheep prepared by the method described by Staub. After recuperation (day 3) the animals in the study group (group 1) underwent intramedullary nailing of a closed femur without prior reaming; group 2 was treated with reaming and nailing according to AO standards. The reaming procedure led to an acute increase of pulmonary arterial pressure only in group 2 (19.8 +/- 2.1 to 31.0 +/- 4.6 mm Hg). Pulmonary triglyceride levels increased at parallel time points from 18.27 +/- 2.3 to 33.04 +/- 7.37 mg/dL only in group 2. Stimulatory capacity of polymorphonuclear leukocytes (PMNL) increased in the study group and decreased in controls (group 1: 2.652 +/- 0.23 x 10(6) cpm to 3.387 +/- 1.34 x 10(6) cpm; group 2: 2.699 +/- 0.34 x 10(6) cpm to 2.460 +/- 0.187 x 10(6) cpm). Intramedullary nailing caused an increase of lung capillary permeability in both groups; in the study group less damage was seen (group 1: 0.390 +/- 0.0006 to 0.354 +/- 0.011; group 2: 0.391 +/- 0.0004 to 0.336 +/- 0.015; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMed1992

Effect of ascorbic acid on neutrophil functions and hypoxanthine/xanthine oxidase-generated, oxygen-derived radicals.

The chemiluminescence of isolated neutrophils, stimulated with N-formyl-L-methionyl-L-leucyl-L-phenylalanine, latex, lipopolysaccharide from Escherichia coli, zymosan A, or 4 beta-phorbol 12 beta-myristate 13 alpha-acetate was inhibited up to 99% by the dose-dependent oxygen radical scavenging activity of 6 mmol/l ascorbic acid. The chemiluminescence of neutrophils in blood, stimulated with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, or with zymosan A was inhibited 35% or 48%, respectively, by 6 mmol/l ascorbic acid. Ascorbic acid, up to 6 mmol/l, did not inhibit the release of beta-N-acetylglucosaminidase and elastase from isolated neutrophils activated by the above stimulatory agents. During neutrophil/nylon fibre interaction ascorbic acid reduced the oxygen radical production dose-dependently (77% inhibition of the chemiluminescence response at 6 mmol/l ascorbic acid), whereas the adherence was unaffected. Hypoxanthine/xanthine oxidase-generated oxygen radicals were scavenged by ascorbic acid in a dose-dependent manner (99% inhibition of the chemiluminescence response at 100 mumol/l ascorbic acid). From these results, ascorbic acid can highly be recommended for animal experiments and clinical studies in patients with trauma, shock and sepsis and for studies to prevent or reduce reperfusion injuries.

Antioxidants↗
PubMed1992

Determination of human neutrophil elastase in bronchoalveolar lavage fluid: homogeneous immunoactivation versus heterogeneous enzyme immunoassay.

Elastase mass concentrations of bronchoalveolar lavage fluid were determined by a homogeneous immunoactivation and a heterogeneous enzyme immunoassay. There was an excellent correlation between both assay systems (y = 1.0376 . x + 1.311; r = 0.9901; n = 43) indicating the suitability of the immunoactivation method for the determination of elastase concentrations in bronchoalveolar lavage fluid as a matrix. Furthermore, dilution of bronchoalveolar lavage fluid samples did not influence the elastase recovery of either assay system.

Bronchoalveolar Lavage Fluid↗
PubMed1991

[Does lung contusion and general injury severity have an effect on the lung following intramedullary femoral nailing? An animal model].

We evaluated changes in lung function after closed intramedullary femoral nailing (IMN) in sheep. The effects of isolated IMN were compared with those of nailing after lung contusion and hemorrhagic shock. In adult female merino sheep a chronic lung lymph fistula was prepared according to the method described by Staub. At day 1, group 1 received right-sided lung contusion and hemorrhagic shock to a mean blood pressure of 50 mmHg for 2 h. Group 2 was the control group. At day 3 both groups were submitted to IMN, followed by a 2-h observation period. IMN caused a transient significant increase in pulmonary artery pressure and central venous triglycerides in both groups. Chemiluminescence of isolated polymorphonuclear leukocytes (PMNL) decreased in group 1 from 2.699 +/- 0.344 to 2.460 +/- 0.187 x 10(6) cpm/25000 PMNL and increased in group 2 from 2.757 +/- 0.127 to 3.824 +/- 0.439 x 10(6) cpm/25000 PMNL. Lymph flow in group 1 increased 1.5-fold while microvascular pressure decreased. In group 2 lymph flow increased less, while MVP increased. The filtration coefficient in group 1 was 5 times (7.533 +/- 0.044) that in the control group (1.45 +/- 0.133). Calculations of permeability indicated a 2-fold increase (0.044 group 1 vs 0.026 group 2). In the presence of previous lung contusion and hemorrhagic shock there is definite lung damage from IMN. This is probably mediated by stimulation of PMNL.

Animals↗