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A Bauer

Publications and source records attributed to A Bauer.

At least 91 records · Page 5Linked to original sources

The Continuum of Water Vapor Mixed with Methane: Absolute Absorption at 239 GHz and Linewidth Calculations.

In the aim of achieving a better understanding of the molecular mechanisms involved in the absorption continuum of the water-vapor rotational spectrum, various H(2)O-X mixtures are investigated in an atmospheric window in the mmw range. In the present study, the X mixing gas is methane. Absolute absorption rates have been measured at 239 GHz. The dependence on pressure as well as temperature has been obtained. The experimental data are compared with models using conventional line profiles. As these models require the knowledge of the collisional half-widths of H(2)O broadened by CH(4), theoretical calculations using the complex Robert-Bonamy formalism have been carried out. A "continuum effect" is observed when comparing the experimental absorption with the models, as well as for the magnitude of the absorption discrepancy and for the strong temperature dependence of this absorption. The effect is compared for various X mixing gases to the collisional broadening efficiency in the impact approximation. Copyright 2000 Academic Press.

Journal Article↗

[Safety and feasibility of intracoronary brachytherapy with the Novoste system within the scope of international multicenter studies].

UNLABELLED: Clinical trials are increasingly investigating the effects of intracoronary radiation for the treatment of de-novo lesions, restenosis (without stents), and in-stent restenosis. As the first group in Germany, we had the opportunity to use the Novoste system within the international multicenter studies BETA-CATH, START and BRIE and report our preliminary experience regarding safety and feasibility of intracoronary brachytherapy with this afterloader. A total of 95 patients were enrolled. The Novoste system was used in 92 patients (104 lesions). Ischemic complications were not observed; therefore, radiation was performed as planned. The mean applied dose was 16 +/- 2 Gy (14-20 Gy, at 2 mm distance) and mean exposure time was 202 +/- 27 s (165-261 s). The addition of brachytherapy increased the total duration of the intervention for 17 +/- 8 min. At the body surface of the patients, the following dose rates were measured: left chest wall: 99 +/- 52 microSv/h; groin 3 +/- 3 microSv/h. All patients received ASS 300 mg/d o.d. Patients with stent implantation in the same session received 250 mg b.i.d. Ticlopidin or 75 mg Clopidogrel o.d. for at least three months. Total mortality and infarct rate was 0. There was no acute, subacute or late stent thrombosis. CONCLUSION: Our first experience with the Novoste Beta-Cath system showed that intracoronary brachytherapy can be safely and simply performed in the cath lab. There were no acute complications. To avoid the possible risk of late stent thrombosis, Ticlopidin or Clopidogrel must be administered for at least three months.

Aged↗

[Evaluation of syncope in geriatric patients: normal values, complications and outcome of invasive electrophysiological study].

Invasive electrophysiologic study (EPS) is an important tool in the assessment of patients with unexplained syncope. Especially in the elderly, the need for a complete diagnostic work-up is counterbalanced by the fear of complications associated with invasive procedures. Thus, the present study specifically addressed the question whether the risk/benefit ratio of EPS in geriatric patients with unexplained syncope justifies this invasive procedure. An invasive EPS was performed in 96 patients between 70 and 80 years and 21 patients older than 80 years. The control group consisted of 65 patients younger than 40 years. With increasing age, the diagnostic yield of EPS also increased (positive EPS finding in 20% of the control group and in 54% of the oldest patients). The majority of complications were of minor clinical significance and no significant differences were found between the three groups. Finally, no age-related difference in measured standard electrophysiological parameters was evident. Due to the high diagnostic value and the low complication rate, EPS can be recommended in elderly patients with unexplained syncope. An age-specific standardization of electrophysiologic parameters, measured during EPS, does not seem to be required.

Aged↗

Molecular genetic dissection of glucocorticoid receptor function in vivo.

Glucocorticoids are involved in numerous physiological processes. Most of their effects are mediated by the glucocorticoid receptor (GR) via activation and repression of gene expression. Whereas activation requires DNA binding of the receptor, repression is usually mediated by protein-protein interactions with other transcription factors. To decipher the molecular mode of action of GR, mice were generated by gene targeting, carrying a point mutation in one of the dimerization domains, thus abrogating DNA binding by GR. These GRdim mice survive to adulthood and thereby allowed analysis of the mechanism used by GR in the control of physiological processes. Specifically, stress erythropoiesis was found to require the DNA binding-dependent function of GR whereas the antitumor-promoting activity of GR in skin is mediated by interaction with the transcription factor AP-1. Furthermore, the immunosuppressive and anti-inflammatory activity of glucocorticoids is largely independent of GR DNA-binding, suggesting that GRdim mice might be useful in the future for the search of steroidal anti-inflammatory drugs with reduced side-effects.

Animals↗

Cesium chloride induced ventricular arrhythmias in dogs: three-dimensional activation patterns and their relation to the cesium dose applied.

INTRODUCTION: Cesium chloride has widely been used in experimental models to produce various ventricular arrhythmias. The study was designed to evaluate whether type and mechanism of these arrhythmias are dose-dependent. METHODS: In 7 dogs with acute AV-block, 60 pins containing 4 bipolar electrodes each were inserted into both ventricles to provide 240 endo-, epi- and midmyocardial recording sites. A computerized mapping system was used to determine three-dimensional activation patterns of ventricular arrhythmias induced by three injections of 1 mmol/kg cesium chloride at 20 minute intervals. RESULTS: Out of all arrhythmias induced, 25 ventricular extrasystoles, 31 monomorphic and 47 polymorphic ventricular tachycardias were mapped. Nonsustained ventricular tachycardias were readily inducible by a single bolus of cesium chloride, whereas sustained episodes required repetitive injections (1.45 +/- 0.61 vs. 2.61 +/- 0.57 doses, p < 0.05). Polymorphic tachycardias were observed more commonly than monomorphic tachycardias (87 vs. 31). Initiation and maintenance of cesium induced arrhythmias were exclusively based on focal mechanisms originating from the subendocardium, irrespective of morphology and dosage. All monomorphic arrhythmias were caused by repetitive firing of single immobile foci located in either the right or the left ventricle. Bi- and multifocal mechanisms, however, were found to underlie the polymorphic episodes. CONCLUSIONS: Although there is a dose-dependence as to the sustenance of mono- or polymorphic tachycardias, this does not reflect on the three-dimensional activation pattern of cesium induced arrhythmias, which are due to mono- or multifocal activation originating from the subendocardium.

Animals↗

Electrophysiologic effects of the new I(Ks)-blocking agent chromanol 293b in the postinfarction canine heart. Preserved positive use-dependence and preferential prolongation of refractoriness in the infarct zone.

OBJECTIVES: Aim of the present study was to investigate site- and rate dependent effects of the IKs-blocking agent chromanol 293b on conduction and refractoriness in normal, infarcted, and transitional regions of in-situ canine hearts. METHODS: In five dogs with subacute myocardial infarction, three-dimensional mapping was performed after insertion of 6 x 6 needle electrodes in the left ventricle. Before and after application of chromanol 293b (10 mg/kg), activation patterns and local refractory periods (ERPs) at pacing intervals of 300, 500 and 850 ms were obtained for the surviving epicardial muscle layer of the infarct zone (IZ) and for epi-, endo-, and midmyocardial muscle layers of both the normal zone (NZ) and the border zone (BZ) separating normal and infarcted areas. RESULTS: At baseline, both the NZ and the BZ exhibited uniform ERPs throughout the ventricular wall. Epicardial ERPs were longer in the IZ than in the NZ, and intermediate in the BZ. Chromanol 293b did not affect total activation times. However, at fast heart rates regional areas of slow conduction occurred. Chromanol 293b ubiquitously prolonged local ERPs, most markedly in the IZ. A preferential effect on individual muscle layers of the NZ or BZ and, thus, drug-induced transmural dispersion of ERP could not be observed. Again ubiquitously, the effect on ERP was more pronounced at faster than at slower heart rates, that is, positive use-dependent. At a basic cycle length of 300 ms, chromanol 293b prolonged local ERPs in the IZ by 46 +/- 24 %, in the BZ by 34 +/- 26%, and in the NZ by 20 +/- 17% (p < or = 0.05). CONCLUSIONS: At least in theory, the electrophysiologic properties of chromanol 293 b, that is, preferential prolongation of refractoriness in ischemic myocardium, more pronounced at faster than at slower heart rates, but homogeneously throughout the intact ventricular wall, appear to be favorable. Whether this translates into a clinical benefit, particularly in the treatment of ischemia-related ventricular tachyarrhythmias, remains to be determined.

Animals↗

Homozygous gene deletions of the glutathione S-transferases M1 and T1 are associated with thimerosal sensitization.

OBJECTIVE: Thimerosal is an important preservative in vaccines and ophthalmologic preparations. The substance is known to be a type IV sensitizing agent. High sensitization rates were observed in contact-allergic patients and in health care workers who had been exposed to thimerosal-preserved vaccines. There is evidence for the involvement of the glutathione system in the metabolism of thimerosal or its decomposition products (organomercury alkyl compounds). Thus detoxification by polymorphically expressed glutathione S-transferases such as GSTT1 and GSTM1 might have a protective effect against sensitization by these substances. METHODS: To address this question, a case control study was conducted, including 91 Central European individuals with a positive patch-test reaction to thimerosal. This population was compared with 169 healthy controls and additionally with 114 individuals affected by an allergy against para-substituted aryl compounds. The latter population was included in order to test whether possible associations were due to substance-specific effects, or were a general feature connected with type IV immunological diseases. Homozygous deletions of GSTT1 and GSTM1 were determined by polymerase chain reaction. RESULTS: Glutathione S-transferase M1 deficiency was significantly more frequent among patients sensitized to thimerosal (65.9%, P = 0.013) compared with the healthy control group (49.1%) and the "para-compound" group (48%, P = 0.034). Glutathione S-transferase T1 deficiency in the thimerosal/mercury group (19.8%) was barely elevated versus healthy controls (16.0%) and the "para-compound" group (14.0%). The combined deletion (GSTT1-/GSTM1-) was markedly more frequent among thimerosal-sensitized patients than in healthy controls (17.6% vs. 6.5%, P = 0.0093) and in the "para-compound" group (17.6% vs. 6.1%, P =0.014), revealing a synergistic effect of these enzyme deficiencies (healthy controls vs. thimerosal GSTM1 negative individuals, OR = 2.0 [CI = 1.2-3.4], GSTT1-, OR = 1.2 [CI = 0.70-2.1], GSTM1/T1-, OR = 3.1 [CI = 1.4-6.5]). CONCLUSIONS: Since the glutathione-dependent system was repeatedly shown to be involved in the metabolism of thimerosal decomposition products, the observed association may be of functional relevance.

Adolescent↗

Differential influence of Pomphorhynchus laevis (Acanthocephala) on the behaviour of native and invader gammarid species.

Although various species of acanthocephalan parasites can increase the vulnerability of their amphipod intermediate hosts to predation, particularly by altering their photophobic behaviour, their influence on the structure of amphipod communities and the success of invader species has so far received little attention. We compared the prevalence and behavioural influence of a fish acanthocephalan parasite, Pomphorhynchus laevis, in two species of amphipods, Gammarus pulex and Gammarus roeseli in sympatry in the river Ouche (Burgundy, eastern France). There, G. pulex is a resident species, whereas G. roeseli is a recent coloniser. Both uninfected G. pulex and G. roeseli were strongly photophobic. although less so in the invading species. However, there was no significant difference in reaction to light between infected and uninfected G. roeseli, whereas infected G. pulex were strongly photophilic. We discuss our results in relation to the parasite's ability to manipulate invading host species, the possibility that resistant individuals have been selected during the invasion process, and the role that acanthocephalan parasites can play in shaping the structure of amphipod communities.

Acanthocephala↗

Multisite pacing for prevention of atrial tachyarrhythmias: potential mechanisms.

OBJECTIVES: To determine the effects of single-, dual-, triple- and quadruple-site atrial pacing on atrial activation and refractoriness in normal canine hearts. BACKGROUND: Multisite pacing has been suggested to be superior to single-site pacing for prevention of atrial tachyarrhythmias. However, the underlying electrophysiological mechanisms are undetermined at the moment, as is the rationale for the selection of pacing locations and the number of pacing sites. METHODS: In 13 normal beagle dogs, an epicardial multielectrode (128 bipoles) and a multiplexer mapping system were used to reconstruct epicardial atrial activation patterns obtained during simultaneous stimulation from up to four electrodes located in the high and low right and left atrium, respectively. For all pacing modes (single-, dual-, triple- and quadruple-site pacing), total activation times and local effective refractory periods at eight randomly selected sites as well as local recovery intervals were determined. In a subgroup of five dogs, total epicardial activation times were also obtained during single-site septal stimulation (septal group). RESULTS: Activation times and local recovery intervals were minimized by triple-site stimulation, whereas a fourth site did not produce further shortening. Septal stimulation produced epicardial activation times comparable to quadruple-site stimulation. Local refractory periods and their dispersion always remained unaffected. Functional conduction blocks apparent during single-site were found to resolve during multisite stimulation. CONCLUSIONS: Multisite pacing can prevent functional conduction blocks by multidirectional excitation and a reduction in total activation time. Triple-site and, possibly, septal pacing modes are expected to be most efficient because both minimize total activation times and maximize the multidirectionality of excitation. In spite of unaffected local refractory periods, the shortening of local recovery intervals might homogenize atrial repolarization and, thus, contribute to the preventive effects of multisite pacing.

Animals↗

Expression of Xenopus homologs of the beta-catenin binding protein pontin52.

Identification of pontin52 as an interaction partner of the Wnt/Wg signal transducer beta-catenin implicated a role for this protein in Wnt signaling. Here we describe the isolation of two Xenopus homologs of pontin52, Xpontin and Xreptin, and report the first expression pattern of vertebrate pontin52 homologs. Whole-mount in situ hybridization studies reveal a strong expression of Xpontin in neural crest cells and in later stages in different gastrointestinal organs. Xreptin is also expressed in neural crest cells, in particular in a subpopulation that give raise to the adrenal medulla.

ATPases Associated with Diverse Cellular Activitie↗

[Are cross-eyed persons worse drivers? The effect of stereoscopic disparity on driving skills].

BACKGROUND: The motorist obtains about 90% of the information required to drive a vehicle from the sense of vision. In road traffic, various situations with respect to size, distance, and position have to be evaluated at different speeds. Does depth perception based on disparity play an essential role in these situations? METHODS: Each of ten subjects with defective stereopsis due to strabismus was compared with an age matched healthy control, who was also matched in yearly mileage, type of vehicle and duration of driving experience. After ophthalmological examination including stereotests for both distance and near, all subjects performed the following driving tests: (1) Stopping as close as possible in front of an obstacle, (2) reversing into a parking position, (3) driving a slalom parcours at the speed of 40 km/h, (4) estimating the relative position of two cars within a limited time while approaching them with 40 km/h. All tests were performed both under monocular (the non-leading eye covered) and binocular conditions. The sequence of the tests was randomized in order to minimize training effects. RESULTS: Comparing the driving performance of both groups, the controls performed significantly better (p < 0.01; ANOVA) only in the "slalom task". In "estimation of position" the controls performed significantly worse (p < 0.01; ANOVA) compared to their counterparts with defective stereopsis. A significant difference between the monocular and binocular performance was found only in the "stopping task", exclusively for the group of normals, benefitting from the binocular performance (p < 0.05; ANOVA). CONCLUSION: Stereopsis improves the driving performance only in dynamic situations at intermediate distances.

Adult↗

[Stimulated acoustic emissions with the ultrasound contrast medium levovist: a clinically useful contrast effect with liver-specific properties].

PURPOSE: The purpose of this study was systematically to investigate stimulated acoustic emission (SAE) with the microbubble contrast agent Levovist (Schering AG, Berlin) in vivo with regards to reproducibility, distribution in various organs over time, dependence on technical factors, and influence on the delineation of focal liver lesions. PATIENTS AND METHODS: 2 intravenous injections of 1 g of Levovist were given to 2 dogs and 1-6 injections of 2.5 g Levovist to 5 healthy volunteers and 37 patients. The liver, spleen, large abdominal vessels, and kidney were intermittently scanned for up to 30 min. Studies were evaluated for the presence of SAE signals by 2 observers. In 20 patients with focal liver lesions (15 with metastases, 4 haemangiomata, 1 hepatocellular carcinoma, and 1 cyst) the influence on lesion visualization was also assessed. RESULTS: SAE effects, lasting up to 30 minutes, were seen in all subjects in the liver and spleen. Vascular and renal SAE signals were noted shortly after injection, lasting up to 6 minutes. SAE was absent or markedly reduced in focal liver lesions, which were seen as colour voids. This increased the conspicuity of focal lesions, and in 5 patients additional metastases were detected that could not be delineated on B-mode alone. CONCLUSION: A liver- and spleen-specific late phase of Levovist can be consistently demonstrated using SAE and the effect increases the conspicuity of focal liver lesions.

Adult↗

[Comparison of bolus and infusion of the ultrasound contrast media levovist for color doppler ultrasound of renal arteries].

PURPOSE: To investigate if the duration of Doppler enhancement of the ultrasound contrast agent Levovist can be prolonged by continuous infusion compared to bolus injections in patients. METHODS: 12 patients with suspected renal artery stenosis were included. Each patient received 1 or 2 bolus injections of 4 g each and a "fast" infusion of 3 ml/min (average dose: 7 g) of Levovist. In 8 patients an additional "slow" infusion of 1 ml/min (average dose 4.2 g) was given. The duration of "strong" Doppler signal enhancement and the visualization of vessels were compared. RESULTS: The duration of strong enhancement was substantially prolonged by the slow infusion (bolus 6:21 min, fast infusion: 8:57 min, slow infusion: 15:12 min, p < 0.001). The dose effectiveness (duration of strong enhancement per 1 g Levovist) was markedly improved from 0:57 min (bolus) to 3:36 min (slow infusion). Visualisation of the renal arteries was more complete with the slow infusion. CONCLUSION: Levovist infusions at 1 ml/min are superior to bolus injections in the assessment of renal arteries. They prolong the enhancement, make more efficient use of a given dose of contrast material and thus allow additional clinically relevant information to be obtained at reduced cost.

Adult↗

Pathophysiologic role of oxygen free radicals in acute pancreatitis: initiating event or mediator of tissue damage?

BACKGROUND AND OBJECTIVE: Oxidative stress is an important factor in the pathogenesis of acute pancreatitis, as shown in vivo by the beneficial effects of scavenger treatment and in vitro by the potential of free radicals to induce acinar cell damage. However, it is still unclear whether oxygen free radicals (OFR) act only as mediators of tissue damage or represent the initiating event in acute pancreatitis in vivo as well. In the present study the authors aimed to address this issue in an experimental set-up. MATERIALS AND METHODS: Two hundred male Wistar rats were randomly assigned to one of the following experimental groups. In two groups, acute necrotizing pancreatitis was induced by retrograde intraductal infusion of 3% sodium taurocholate. Through the abdominal aorta, a catheter was advanced to the origin of the celiac artery for continuous regional arterial (CRA) pretreatment with isotonic saline (NP-S group) or superoxide dismutase/catalase (NP-SOD/CAT group). In another group, oxidative stress was generated by CRA administration of xanthine oxidase and intravenous administration of hypoxanthine (HX/XOD group). Sham-operated rats received isotonic saline both arterially and intraductally. After observation periods of 5 and 30 minutes and 3 and 6 hours, the pancreas was removed for light microscopy and determination of reduced glutathione (GSH), oxidized glutathione (GSSG), conjugated dienes (CD), and malondialdehyde as a marker for OFR-induced lipid peroxidation as well as myeloperoxidase as a parameter for polymorphonuclear leukocyte accumulation. RESULTS: A significant decrease of GSH was paralleled by an increased ratio of GSSG per total glutathione and elevated CD levels after 5 minutes in the NP-S group versus the sham-operated group. Thereafter, the percentage of GSSG and GSH returned to normal levels until the 6-hour time point. After a temporary decrease after 30 minutes, CD levels increased again at 3 hours and were significantly higher at 6 hours in contrast to sham-operated rats. Myeloperoxidase levels were significantly elevated at 3 and 6 hours after pancreatitis induction. In contrast to NP-S rats, treatment with SOD/CAT significantly attenuated the changes in glutathione metabolism within the first 30 minutes and the increase of CDs after 6 hours. HX/XOD administration lead to changes in levels of GSH, GSSG, and CDs at 5 minutes as well as to increased myeloperoxidase levels at 3 hours; these changes were similar to those observed in NP-S rats. Acinar cell damage including necrosis was present after 5 minutes in both NP groups, but did not develop in HX/XOD rats. In addition, serum amylase and lipase levels did not increase in the latter group. SOD/CAT treatment significantly attenuated acinar cell damage and inflammatory infiltrate compared with NP-S animals during the later time intervals. CONCLUSION: OFRs are important mediators of tissue damage. However, extracellular OFR generation alone does not induce the typical enzymatic and morphologic changes of acute pancreatitis. Factors other than OFRs must be involved for triggering acute pancreatitis in vivo.

Animals↗

Motor cortex fatigue in sports measured by transcranial magnetic double stimulation.

PURPOSE: Besides peripheral mechanisms, central fatigue is an important factor limiting the performance of exhausting exercise in sport. The mechanisms responsible are still in discussion. Using noninvasive transcranial magnetic stimulation (TMS) in a double-pulse technique, we sought to assess fatigue of the motor cortex after exhaustive anaerobic strain. METHODS: 23 male subjects (22-52 yr) taking part in the study were requested to accomplish as many pull-ups as possible until exhaustion. The amount of physical lifting work was recorded. Before and immediately after the task, intracortical inhibition (ICI) and facilitation (ICF) were measured by a conditioned-test double-pulse TMS method for the right brachioradialis (BR) and abductor pollicis brevis muscle (APB). RESULTS: After exercise, ICF was significantly reduced in the BR but not in the APB. ICI was not altered. Changes tended to normalize within 8 min after the task. The amount of lifting work accomplished showed significant correlation to the values of ICF reduction (r = 0.73). Moreover, the baseline values of ICF before exercise were also significantly correlated to the lifting work (r = 0.63). CONCLUSIONS: Because double-pulse TMS gives access to the motor cortex independently of spinal or peripheral mechanisms, reduced ICF reflects decreased excitability of interneuronal circuits within the motor cortex. We suggest that ICF measures motor cortex fatigue after exhausting strain specifically for the muscles performing the task. Gamma-aminobutyric acid (GABA)-ergic neurotransmission is possibly involved in the mechanisms mediating central fatigue. Double-pulse TMS may be a useful tool in the control of training in sports as well as in the detection of pathological central fatigue in overreaching and in the prevention of overtraining.

Adult↗

Mice with an increased glucocorticoid receptor gene dosage show enhanced resistance to stress and endotoxic shock.

Targeted mutagenesis of the glucocorticoid receptor has revealed an essential function for survival and the regulation of multiple physiological processes. To investigate the effects of an increased gene dosage of the receptor, we have generated transgenic mice carrying two additional copies of the glucocorticoid receptor gene by using a yeast artificial chromosome. Interestingly, overexpression of the glucocorticoid receptor alters the basal regulation of the hypothalamo-pituitary-adrenal axis, resulting in reduced expression of corticotropin-releasing hormone and adrenocorticotrope hormone and a fourfold reduction in the level of circulating glucocorticoids. In addition, primary thymocytes obtained from transgenic mice show an enhanced sensitivity to glucocorticoid-induced apoptosis. Finally, analysis of these mice under challenge conditions revealed that expression of the glucocorticoid receptor above wild-type levels leads to a weaker response to restraint stress and a strongly increased resistance to lipopolysaccharide-induced endotoxic shock. These results underscore the importance of tight regulation of glucocorticoid receptor expression for the control of physiological and pathological processes. Furthermore, they may explain differences in the susceptibility of humans to inflammatory diseases and stress, depending on individual prenatal and postnatal experiences known to influence the expression of the glucocorticoid receptor.

Adrenocorticotropic Hormone↗

B-mode enhancement at phase-inversion US with air-based microbubble contrast agent: initial experience in humans.

Pulse- or phase-inversion ultrasonography (US) sums the signals returned from two 180 degrees ultrasound pulses. Linear scattering from tissue results in a signal void while nonlinear signals from microbubbles stand out. The technique was applied with a US contrast agent in 39 human subjects. B-mode enhancement of vessels and organ parenchyma was seen in all cases. Enhancement occurred from flowing and stationary microbubbles. The flow-independent enhancement of normal and abnormal tissue represents a major advance in contrast material-enhanced US with many potential applications especially in tumor imaging.

Adult↗