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Biomedical subjects

W Schwarz

Publications and source records attributed to W Schwarz.

At least 37 records · Page 2Linked to original sources
PubMed2002

Role of ultrasonography in the detection of small adrenal masses.

AIM: Computed tomography (CT) scanning is commonly used for evaluation of adrenal masses in adults. In this prospective study we evaluated whether adrenal gland masses of less or equal than 20 mm in diameter could be detected by modern abdominal ultrasonography (US). METHOD: Between July 1999 and June 2000, 44 consecutive patients with 50 adrenal masses documented by contrast-enhanced CT (left adrenal gland, n = 31; right adrenal gland, n = 19; bilateral, n = 6; median size, 15 [5 +/- 80] mm) and, additionally, 50 patients without CT findings of an adrenal mass were prospectively evaluated by high-resolution US performed by physicians. Based upon CT measurement, 34 adrenal masses were </= 20 mm and 16 were > 20 mm in diameter. RESULTS: The overall sensitivity of US for the detection of adrenal masses was 96 % (48/50) (94 % [29/31] for left and 100 % [19/19] for right adrenal masses, respectively). The overall specificity of US for the detection of adrenal masses was 92 % (92/100) (90 % [45/50] for left and 94 % [47/50] for right adrenal masses, respectively). Thus, the diagnostic accuracy of US for the detection of adrenal masses is 93 % (140/150). Sensitivity and specificity of US for the detection of adrenal masses </= 20 mm (n = 34) did not differ significantly from those > 20 mm (n = 16). CONCLUSION: US is effective for detecting small adrenal masses. In rare cases small masses of the left adrenal gland might be missed and nodular adrenal hyperplasia or retroperitoneal lymph nodes might be misinterpreted as adrenal masses.

Adrenal Gland Neoplasms↗
PubMed2002

[MRI vs. arthroscopy in the diagnosis of cartilage lesions in the knee. Can MRI take place of arthroscopy?].

INTRODUCTION: The accuracy of magnet resonance imaging in diagnosing cartilage lesions is discussed controversially. The sensitivity of this examination ranges from 15 % to 96 %. Clinical evidence demonstrates that cartilage lesions, diagnosed by MRI, were not confirmed in arthroscopy. The purpose of this prospective study was to analyse the practicability of replacing arthroscopy by MRI in diagnosis of cartilage lesions. PATIENTS AND METHODS: 195 patients with acute or chronic knee pain were examined by reason of a pathological clinic result by MRI preoperatively. In group A (n = 86), a standard program was performed in the radiological department of German Army Hospital (sagittal STIR TSE und PD TSE, coronary und transversal T2 FFE [TR = 660 ms, TE = 18 ms, FA = 30 degrees, 512er-Matrix]), in 21 patients (subgroup AK) a cartilage specific sequence (fs T1 W FFE) without gadolinium was added. Patients in group B (n = 88) were examined in a private outpatient clinic (sagittal T1 SE, T2 SE and T2 FLASH [TR = 608 ms, TE = 18 ms, FA = 20 degrees, 256er-Matrix]) with the use of gadolinium. A clear clinical diagnosis had to be performed before MRI examination. RESULTS: 156 lesions of the cartilage were detected arthroscopically. The sensitivity of the examination was in group A 33 %; group B 53 %; group AK 38 %, specificity in group A 99 %; group B 98 % and group AK 98 %. The positive and negative predictive values were in group A 75 %/98 %; group B 48 %/98 % and in group AK 50 %/97 %. CONCLUSION: MRI was not able to detect reliable cartilage lesions. Until now, arthroscopy is the golden standard to detect cartilage lesions.

Arthroscopy↗
PubMed2001

[Early contributions from Erlangen to the theory and practice of general anesthesia with ether and chloroform. 2. The animal experiments of Ernst von Bibra and Emil Harless].

Just three months after the first application of sulphuric ether to a patient in german-speaking countries the monography Die Wirkung des Schwefeläthers in chemischer und physiologischer Beziehung was published. In this book Ernst von Bibra and Emil Harless presented their experimental research on the effects of ether on humans and compared it to those on animals. The contents of the book are described. The authors "Theory on the action of ether" will be discussed in the context of contemporary criticism. Their hypothesis affected the discussion on the mechanisms of anaesthetic action up to the twentieth century.

Anesthesia, General↗
PubMed2001

[Contrast medium enhanced magnetic resonance tomography of liver metastases: positive versus negative contrast media].

The development in oncologic liver surgery as well as modified interventional therapy strategies of the liver have resulted in improved diagnostic imaging. The evolution of contrast agents for MR imaging of the liver has proceeded along several different paths with the common goal of improving liver-lesion contrast. In MRI contrast agents act indirectly by their effects on relaxation times. Contrast agents used for hepatic MR imaging can be categorized in those that target the extracellular space, the hepatobiliary system, and the reticuloendothelial system. The first two result in a positive enhancement, the last one in a negative enhancement. Positive enhancers allow a better characterization of liver metastases using dynamic sequence protocols. Detection rate of liver metastases is increased using hepatobiliary contrast-enhanced MRI compared to unenhanced MRI. Negative enhancers, iron oxide particles, significantly increase tumor-to-liver contrast and allow detection of more lesions than other diagnostic methods. Iron-oxide enhanced MRI enables differential diagnosis of liver metastases comparing morphologic features using T2 and T1-weighted sequences.

Contrast Media↗
PubMed2001

[Clinical aspects of liver cirrhoses and its complications and diagnostic problems].

Liver cirrhosis is the end-stage of chronic liver disease with a prevalence of 0.5-0.8 percent in the German population. The main causes are chronic viral hepatitis B and C and alcohol abuse. Liver cirrhosis is often oligosymptomatic and frequently only diagnosed when complications occur (laboratory tests, ultrasound, computertomography or nuclear resonance imaging and histology). Complications include portal hypertension, gastrointestinal bleeding, ascites, spontaneous bacterial peritonitis, hepatorenal syndrome, hepatopulmonary syndrome, hepatic encephalopathy and hepatocellular carcinoma. Therapeutic management should mainly focus on the treatment of the underlying chronic liver disease in a precirrhotic stage. In the case of cirrhosis, prevention and treatment of complications are clinically most important.

Diagnosis, Differential↗
PubMed2001

[Transjugular portosystemic stent shunt (TIPSS) as intervention in clinical complications of portal hypertension].

Most frequent complications in patients with liver cirrhosis are due to portal hypertension. Beside ascites circumvent vessels formate with vasodilatation. Due to counterregulation a secondary hyperaldosteronism develops with release of vasocontrictive agents. If conservative and endoscopic methods fail, indication for building a portosystemic shunt is given. The TIPSS procedure is less invasive than the surgical method of Warren-Shunt, so the radiological intervention has replaced surgery. Reducing the portal pressure by the shunt, the clinical complications change for the better. Still problems are defined as hepatic encephalopathy and right ventricular heart failure. Regular follow up investigations have to be performed to detect complications in the shunt. Using regular clinical and radiological check up TIPSS is of clinical benefit with good long term results.

Diagnostic Imaging↗
PubMed2001

[Diagnostic imaging of hepatocellular carcinoma. Examination technique, results and indications].

PURPOSE: Demonstration of imaging techniques for the diagnosis and interventional follow up of hepatocellular carcinoma. MATERIAL AND METHODS: Examination strategies are presented using color coded duplex-sonography (US), computed tomography and magnetic resonance techniques like MRI, MR-angiography and MR-cholangiopancreaticography (MRCP). RESULTS: Color coded sonography reveals a sensitivity of 85-92% and a specificity of 78-90% for the detection of HCC. The diagnostic results of CT could be further improved via the newly developed techniques of multislice-CT. The highest diagnostic accuracy could be achieved via the use of contrast enhanced MRI with advantageous results for superparamagnetic contrast agents versus hepatobiliary and extracellular drugs. CONCLUSION: Contrast enhanced MRI proves as the superior imaging technique for the early diagnosis, differential diagnosis and follow up of hepatocellular carcinoma.

Carcinoma, Hepatocellular↗
PubMed2001

RNA from heart of young and old rats leads to the expression of protein(s) in Xenopus oocytes that alter the transport activity of rat Na+,K+-ATPases differently.

To address the question of whether the function of Na+,K+-ATPases differs in the heart of young and old rats, enzymes formed from the alpha1 or alpha2 isoform with the beta1 subunit of rat were expressed in Xenopus oocytes. In addition to injections of the cRNA coding for the respective subunits, oocytes were co-injected with total RNA from the left ventricle of young or old rats. To assess alterations in transport activity due to the co-injections, ouabain-sensitive 86Rb+ uptake was measured. Co-injection of the RNA from young rats led to 31% inhibition of 86Rb+ uptake into oocytes with the alpha1/beta1 pumps while uptake into oocytes with the alpha2/beta1 pumps was hardly affected. Co-injection of the RNA from old rats, on the other hand, reduced 86Rb+ uptake only in cells with the alpha2/beta1 isoform (to 85%). The steady-state current generated in the absence of external Na+ by the alpha1/beta1 ATPase was significantly reduced by co-injection of RNA only from young rats to 70%, and this inhibition was hardly affected by membrane potential. For the alpha2/beta1 ATPase co-injection of RNA only from old rats also led to a significant reduction of pump-mediated current at potentials more negative than -70 mV to 70-80%. In the presence of Na+, inhibition of the alpha1 isoform by co-injection of RNA from young rats is voltage-dependent, increasing with more negative potentials. For the alpha2/beta1 pump, co-injection of RNA from old rats was no longer effective, but voltage-dependent inhibition by co-injection of RNA from young rats became apparent. The data indicate that changes in protein expression occurring in young and old rat hearts may modulate transport activity of the Na+,K+-ATPase and this modulation depends on membrane potential and the presence of external Na+. We propose that the described mechanisms may play a functional role in working myocardium, and may form a basis for processes involved in heart aging.

Aging↗
PubMed2001

Molecular characterization of co-transcribed genes from Streptomyces tendae Tü901 involved in the biosynthesis of the peptidyl moiety and assembly of the peptidyl nucleoside antibiotic nikkomycin.

Six genes (nikP1, nikP2, nikS, nikT, nikU, and nikV) from Streptomyces tendae Tu901 were identified by analysis of the nucleotide sequence of the nikkomycin gene cluster. These genes, together with the previously described nikQ and nikR, span 9.39 kb and are transcribed as a polycistronic mRNA in a growth-phase-dependent manner. The nikP1 gene encodes a non-ribosomal peptide synthase consisting of an adenylation domain, a thiolation domain, and an N-terminal 70-residue segment of unknown function. The amino acid sequence encoded by the nikP2 gene displays similarity to the sequences of thioesterases, and the nikS product belongs to a superfamily of proteins characterized by a specific ATP-binding fold. The N-terminal 70 amino acids of the predicted nikT gene product show significant sequence similarity to acyl carrier proteins, and the C-terminal 330 amino acids to aminotransferases. The sequences of the deduced proteins NikU and NikV exhibit similarity to components S and E, respectively, of glutamate mutase from Clostridium. Disruption of the nikP1, nikS, nikT, or nikV gene by insertion of a kanamycin resistance cassette abolished formation of nikkomycins I, J, X, and Z, all of which contain hydroxypyridylhomothreonine as the peptidyl moiety. The nikP1 mutants, and the nikS and nikT mutants accumulated the nucleoside moieties nikkomycin Cz, and nikkomycins Cx and Cz, respectively. The nikV mutants formed nikkomycins Ox and Oz, which contain 2-amino-4-hydroxy-4-(3'-hydroxy-6'-pyridyl) butanoic acid as the peptidyl moiety. The nikP2 mutants synthesized nikkomycins I, J, X, and Z, but amounts of nikkomycins I and X, which contain formylimidazolone as the base, were lower. Feeding formylimidazolone to nikP2 mutants restored the ability to form nikkomycins I and X. Our results indicate that nikU and nikV are required for the synthesis of hydroxypyridylhomothreonine, the genes nikP1, nikP2 and nikS are required for the assembly of nikkomycins, and nikT is required for both pathways. The putative activities of each of their products are discussed.

Amino Acid Sequence↗
PubMed2001

The ex-Wald distribution as a descriptive model of response times.

We propose a new quantitative model of response times (RTs) that combines some advantages of substantive, process-oriented models and descriptive, statistically oriented accounts. The ex-Wald model assumes that RT may be represented as a convolution of an exponential and a Wald-distributed random variable. The model accounts well for the skew, shape, and hazard function of typical RT distributions. The model is based on two broad information-processing concepts: (1) a data-driven processing rate describing the speed of information accumulation, and (2) strategic response criterion setting. These concepts allow for principled expectations about how experimental factors such as stimulus saliency or response probability might influence RT on a distributional level. We present a factorial experiment involving mental digit comparisons to illustrate the application of the model, and to explain how substantive hypotheses about selective factor effects can be tested via likelihood ratio tests.

Adolescent↗
PubMed2000

Extracellular pH modulates kinetics of the Na(+),K(+)-ATPase.

To investigate effects of pH on the Na(+),K(+)-ATPase, we used the Xenopus oocytes to measure transient charge movements in the absence of extracellular K(+), and steady-state currents mediated by the pump as well as ATPase activity. The activity of purified Na(+), K(+)-ATPase strongly depends on pH, which has been attributed to protonation of intracellular sites. The steady-state current reflects pump activity, the transient charge movement voltage-dependent interaction of external Na(+) ions with the pump molecule and/or conformational changes during Na(+)/Na(+) exchange. The steady-state current exhibits a characteristic voltage dependence with maximum at about 0 mV at low external K(+) (< or =2 mM) and with 50 Na(+). This dependency is not significantly affected by changes in external pH in the range from pH 9 to pH 6. Only below pH 6, the voltage dependence of pump current becomes less steep, and may be attributed to a pH-dependent inhibition of the forward pump cycle by external Na(+). External stimulation of the pump by K(+) in the absence of Na(+) can be described by a voltage-dependent K(m) value with an apparent valency z(K). At higher external pH the z(K) value is reduced. The transient current signal in the absence of external K(+) can be described by the sum of three exponentials with voltage-dependent time constants of about 50 ms, 700 micros and less than 100 micros during pulses to 0 mV. The charge distribution was calculated by integration of the transient current signals. The slowest component and the associated charge distributions do not significantly depend on external pH changes. The intermediate component of the transients is represented by a voltage-dependent rate constant which shows a minimum at about -120 mV and increases with decreasing pH. Nevertheless, the contribution to the charge movement is not altered by pH changes due to a simultaneous increase of the amplitude of this component. We conclude that reduction of external pH counteracts external K(+) and Na(+) binding.

Animals↗
PubMed2000

Functional significance of N- and C-terminus of the amino acid transporters EAAC1 and ASCT1: characterization of chimeric transporters.

To localize functionally significant domains in the amino acid transporters of mouse brain mEAAC1 and mASCT1, cRNA encoding for wild-type and chimeric transporters was injected into Xenopus oocytes. Activity of expressed transporters was investigated by measurements of uptake of 3H-labeled glutamate and serine and of glutamate- and serine-induced currents under voltage clamp. Though all transporters accept glutamate and serine as substrate, the central part of the protein (Ala94-Met418 of mEAAC1 and Ala119-Ile393 of mASCT1) determines substrate selectivity. The C-terminus rectifies the interaction with the respective substrate. A channel mode of the glutamate transporter can be activated by glutamate and serine, and the N- and C-termini of the mEAAC1 seem to be essential for the channel formation.

Amino Acid Sequence↗
PubMed2000

Sequential effects in number comparison.

The modular framework of number processing (e.g., S. Dehaene & R. Akhavein, 1995) was applied to study sequential trial-to-trial effects in a number comparison task. In Experiment 1, numbers were always presented as digits. Responses were faster when the same number was repeated, but this effect was additive with the numerical distance effect. In Experiment 2, numbers were presented either as digits or as words. The authors found significant effects of repeating (a) the same physical stimulus, (b) the same number but in a different notation, and (c) the same notation but a different number. Again, all 3 effects were additive with the numerical distance effect. The authors' results provide strong evidence against accounts according to which, on stimulus repetition trials, the comparison stage is bypassed (as proposed by S. Dehaene, 1996), and the results clearly favor an early, precomparison locus of repetition effects.

Adolescent↗
PubMed2000

Trypanosomes lacking trypanothione reductase are avirulent and show increased sensitivity to oxidative stress.

In Kinetoplastida, trypanothione and trypanothione reductase (TRYR) provide an intracellular reducing environment, substituting for the glutathione-glutathione reductase system found in most other organisms. To investigate the physiological role of TRYR in Trypanosoma brucei, we generated cells containing just one trypanothione reductase gene, TRYR, which was under the control of a tetracycline-inducible promoter. This enabled us to regulate TRYR activity in the cells from less than 1% to 400% of wild-type levels by adjusting the concentration of added tetracycline. In normal growth medium (which contains reducing agents), trypanosomes containing less than 10% of wild-type enzyme activity were unable to grow, although the levels of reduced trypanothione and total thiols remained constant. In media lacking reducing agents, hypersensitivity towards hydrogen peroxide (EC50 = 3.5 microM) was observed compared with the wild type (EC50 = 223 microM). The depletion of TRYR had no effect on susceptibility to melarsen oxide. The infectivity and virulence of the parasites in mice was dependent upon tetracycline-regulated TRYR activity: if the trypanosomes were injected into mice in the absence of tetracycline, no infection was detectable; and when tetracycline was withdrawn from previously infected animals, the parasitaemia was suppressed.

Animals↗
PubMed2000

[Percutaneous transvenous recovery of foreign bodies using a self-made wire loop].

AIM: Several techniques exist to retrieve catheter and guide wire fragments. In this report we summarize our cost-saving method. MATERIALS AND METHODS: A 7-8F guiding catheter and a self-made loop consisting of a 260 cm/0.035 in. Terumowire was used. RESULTS: 45 of 48 fragments were retrieved completely using this method. For the three remaining fragments (all pacemaker electrodes), retrieval was attempted with a "Goose-Neck" loop, two of them failed. The procedure was well tolerated, there were no severe complications. CONCLUSION: Usually venous foreign bodies can be retrieved completely by this cost-saving method, the use of expensive industrial loops or baskets can be avoided.

Angiography↗
PubMed1999

Molecular characterization of co-transcribed genes from Streptomyces tendae Tü901 involved in the biosynthesis of the peptidyl moiety of the peptidyl nucleoside antibiotic nikkomycin.

Six genes (nikA, nikB, nikD, nikE, nikF, and nikG) from Streptomyces tendae Tü901 were identified by sequencing the region surrounding the nikC gene, which encodes L-lysine 2-aminotransferase, previously shown to catalyze the initial reaction in the biosynthesis of hydroxypyridylhomothreonine, the peptidyl moiety of the peptidyl nucleoside antibiotic nikkomycin. These genes, together with the nikC gene, span a DNA region of 7.87 kb and are transcribed as a polycistronic mRNA in a growth-phase dependent manner. The sequences of the deduced proteins NikA and NikB exhibit significant similarity to those of acetaldehyde dehydrogenases and 4-hydroxy-2-oxovalerate aldolases, respectively, which are involved in meta-cleavage degradation of aromatic hydrocarbons. The predicted NikD gene product shows sequence similarity to monomeric sarcosine oxidases, and the deduced NikE protein belongs to the superfamily of adenylate-forming enzymes. The nikF gene and the nikG gene encode a cytochrome P450 monooxygenase and a ferredoxin, respectively. Disruption of any of the genes nikA, nikB, nikD, nikE and nikF by insertion of a kanamycin resistance cassette abolished formation of the biologically active nikkomycins I, J, X, and Z. The nikA, nikB, nikD, and nikE mutants accumulated the nucleoside moieties nikkomycins Cx and Cz. In the nikD and nikE mutants nikkomycin production (nikkomycins I, J, X, Z) could be restored by feeding with picolinic acid and hydroxypyridylhomothreonine, respectively. The nikF mutant exclusively produced novel derivatives, nikkomycins Lx and Lz, which contain pyridylhomothreonine as the peptidyl moiety. Our results indicate that the nikA, nikB, nikD, nikE, nikF, and nikG genes, in addition to nikC, function in the biosynthetic pathway leading to hydroxypyridylhomothreonine, the putative activities of each of their products are discussed.

Aldehyde Oxidoreductases↗