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Biomedical subjects

W Schwarz

Publications and source records attributed to W Schwarz.

At least 73 records · Page 4Linked to original sources
PubMed1997

[Dynamic and static MRI using superparamagnetic MRI contrast medium Resovist for visualizing primary and secondary liver tumors].

PURPOSE: To analyse characteristics of benign and malignant liver tumours in dynamic and static MR imaging with the superparamagnetic MR contrast medium Resovist. MATERIAL AND METHODS: All 30 patients were examined on a 1.5 Tesla MR unit (Magnetom 63 SP, Siemens AG, Erlangen, Germany) using proton density (PD) weighted (w), T2-weighted-spin-echo, a T1-weighted SE, and a T1-weighted FLASH-2 D gradient echo (GRE) sequence before, during and after the application of Resovist. Dynamic imaging was performed using a T2-weighted GRE-sequence (TurboFLASH; TR/TE = 11/30; flip angle = 10 degrees; Tl = 600 ms). Histopathology revealed benign liver lesions in 8 patients and malignant lesions in 22 patients. RESULTS: Dynamic T2-weighted sequence revealed an early loss of signal intensity in normal liver parenchyma (percentage signal intensity loss (PSIL) = 40.0 +/- 12.2% by 4 mumol Fe/kg, 47.2 +/- 18.8% by 8 mumol Fe/kg and 62.7 +/- 13.0% by 16 mumol Fe/kg), in the spleen, as well as in FNH (PSIL = 49.5 +/- 7.3% by 8 mumol Fe/kg), and regenerating nodules in the first minute after application of Resovist. In two of 4 cases with HCC a short drop in signal intensity was immediately observed after the application, whereas signal intensity remained unchanged in all other malignant liver tumours. Enhanced PDw and T2-weighted SE-sequences revealed an improved detection and delineation of malignant liver lesions versus plain MR imaging. 17 liver lesions of a size lower 10 mm were additionally detected in postcontrast T2-weighted SE-sequences in 4 patients. CONCLUSION: Dynamic and static versus plain MR imaging of primary and secondary liver lesions is markedly improved by the superparamagnetic contrast material Resovist, especially in case of intravenous bolus application of this liver-specific contrast medium.

Adult↗
PubMed1997

Association between acute cerebrovascular ischemia and chronic and recurrent infection.

BACKGROUND AND PURPOSE: We performed a case-control study to investigate whether chronic or recurrent respiratory, ear-nose-throat (ENT), and dental infections are risk factors for cerebrovascular ischemia. METHODS: Using a standardized questionnaire we investigated past infectious diseases in 166 consecutive patients with acute cerebrovascular ischemia and in 166 age- and sex-matched nonstroke neurological patient controls. In subgroups, we performed standardized ENT (69 patients, 66 control subjects) and dental examinations including orthopantomography (66 patients, 60 control subjects). Dental status was determined by a total dental index (TDI) that reflects caries, periapical lesions, periodontitis, and other dental lesions and by an orthopantomography index (OPGI) that was assessed blinded. RESULTS: Frequent (> or = 2 episodes in each of the 2 preceding years) or chronic bronchitis was associated with cerebrovascular ischemia in age-adjusted multiple logistic regression analysis (odds ratio, OR, 2.2; 95% confidence interval, CI, 1.04 to 4.6). Groups were not different in ENT examination. Patients tended to have a worse dental status (TDI: P = .070; OPGI: P = .062) and had more severe periodontitis (P = .047) and periapical lesions (P = .027) than control subjects. In age-adjusted multiple logistic regression analysis with social status and established vascular risk factors, poor dental status (TDI) was independently associated with cerebrovascular ischemia (OR, 2.6; 95% CI, 1.18 to 5.7). CONCLUSION: Recurrent or chronic bronchial infection and poor dental status, mainly resulting from chronic dental infection, may be associated with an increased risk for cerebrovascular ischemia.

Acute Disease↗
PubMed1996

Cardiac Na+ pump current-voltage relationships at various transmembrane gradients of the pumped cations.

Thermodynamic considerations predict changes of the Na+ pump current (Ip)-voltage (V) relationship of animal cells upon variations of the electrochemical gradients against which cations must be pumped. Experimental data in support of the predictions are sparse. Therefore, the effect on the Ip-V relationship of various electrochemical gradients for pumped Na+ and Cs+ was studied at constant deltaGATP (approximately -39kJ/mol in cardioballs from sheep Purkinje fibres. Control of the subsarcolemmal ionic concentrations during whole-cell recording was ensured by activation of Ip below its half maximal activity or by measuring the initial Ip following reactivation of the Na+/K+ pump. With gradients close to physiological conditions Ip was outward over the entire voltage range and the Ip-V relationship showed a maximum near zero potential. Steepening the ionic gradients diminished the Ip amplitude and outward pump current was no longer detectable between -65 mV and -110 mV. Flattened ionic gradients increased the Ip amplitude and shifted apparently the reversal potential Erev to more negative values. These changes are in line with theoretical considerations. The measured Ip-V relationships were fitted by curves computed on the basis of a simplified Post-Albers scheme of Na+/Cs+ pumping. The increased Ip amplitude at flat ionic gradients was due to a decrease of [Cs+]o for half maximal Ip activation. The maximal Ip amplitude remained unaffected

Animals↗
PubMed1996

Structure-function relationships of Na+/K(+)-pumps expressed in Xenopus oocytes.

During the last years we have examined structure-function relationships in the Na+/K(+)-ATPase with respect to interactions of the external cations with the pump molecule. We have analysed in voltage-clamp experiments the influence of extracellular Na+ and K+ on the current generated by Na+/K(+)-pumps expressed in Xenopus oocytes. Our results demonstrated that external Na+ and K+ have to pass an access channel in the electrical field of the membrane to reach their binding sites. This external access, therefore, is voltage-dependent and is affected by lysine residues within the cytoplasmic N-terminus, by glutamic acid residues in intramembraneous domains, the ouabain sensitivity and phosphorylation by protein kinases.

Amino Acid Sequence↗
PubMed1996

[Gravity or suction drainage in thyroid surgery? Control of efficacy with ultrasound determination of residual hematoma].

In a prospective randomized trial, the common high-vacuum drainage system according to Redon was compared with the nonsuction system according to Robinson in 80 patients undergoing elective thyroid surgery between January 1995 and August 1995. Forty patients were provided with nonsuction, passive drains, and another 40 patients were allocated to a control group with the high-vacuum system. Twenty-four h postoperatively, the wound area was analyzed by sonography after drainage removal. The dimension of the remaining hematoma was determined by scanning the operation field in six to seven layers (thickness per layer T = 1 cm). The area (A) of the hematoma was measured per layer, and thus the volume was determined by the formula: V = T x (A1 + A2.. + A(n)). Simultaneously, the quantity of discharge was determined. Patients receiving nonsuction drainage had significantly lower median drainage volume (34 ml; range: 0-175 ml vs-115 ml; range: 40-346 ml; P < 0.01) and a remaining hematoma, measured sonographically, of similar volume to that of the patients receiving high-vacuum treatment (4.4 ml; range: 0-21.7 ml vs 5.3 ml; range: 0.6-24.9 ml; not significant). No complications were observed. An advantage to using the nonsuction device is seen with respect to similar resting wound hematoma, lower fluid evacuation, and painless drain removal. This study supports prophylacity routine nonsuction wound drainage after elective thyroid surgery.

Adult↗
PubMed1996

[Early contributions from Erlangen to the theory and practice of ether and chloroform anesthesia. 1. Heyfelder's clinical trial with ether and chloroform].

The era of modern anaesthesia in Germany began on January 24th, 1847. This day, professor in ordinary Johann Ferdinand Heyfelder anaesthetized a patient with sulphuric ether in the clinic of surgery and ophthalmology of the University of Erlangen. By March 17th, 1847, Heyfelder had performed 121 surgical procedures under ether. The operations in majority were teeth-extractions, and a few more complex operations such as the treatment of a harelip or of lip cancer or the resection of the shoulder joint. Heyfelder described in detail 108 of these inhalations in a little book entitled The experiments with sulphuric ether. This monograph published in March, 1847, represents one of the first complete dissertations on sulphuric ether in the German literature. In a special chapter he analyzed the development of various physiological and psychological parameters during etherization. Heyfelder also examined blood and urine of some etherized patients and reported that he did not find any important or specific alterations. In 1847, Heyfelder was probably the first to apply salt-ether in man. After 4 administrations he concluded that salt ether acted more quickly but shorter than sulphuric ether. Advantageous were its application without problems and ease of induction. Disadvantageous were its high volatility, its price and the difficulty of getting it in a pure form. From December, 1847, on Heyfelder started to use chloroform. He was now able to perform more major operations, for example, the total resection of the hip-joint. In his book The experiments with sulphuric ether, salt ether, and chloroform he describes a great number of anaesthetic administrations using these 3 agents. In his summary Heyfelder concluded, that chloroform was undoubtly superior to sulphuric ether mainly because it was a quicker acting and longer lasting agent and leads to deeper narcosis. Moreover its application was much easier for it needed no special apparatus. However, because of its great anaesthetic potency, Heyfelder particularly demanded great caution in the application of chloroform. Explicitely he expected an assistant for chloroformizations, whose only duty was to supervise the inhalations and the patient--a forerunner of the modern specialized anaesthesiologist.

Anesthesiology↗
PubMed1996

Magnetic resonance imaging of focal liver lesions. Comparison of the superparamagnetic iron oxide resovist versus gadolinium-DTPA in the same patient.

RATIONALE AND OBJECTIVES: The authors assess the efficacy of static and dynamic magnetic resonance (MR) imaging using the superparamagnetic iron oxide SHU-555A (Resovist) versus standard dose of gadolinium (Gd)-DTPA in patients with focal liver lesions. METHODS: Magnetic resonance imaging was performed in 30 patients suffering from histopathologically verified malignant (n = 22) and benign (n = 8) liver lesions. T2-weighted conventional and fat-suppressed as well as T1-weighted sequences were used before, during, and after fast intravenous administration of Resovist (1 mL/minute) at three doses of 4, 8, and 16 mumol/kg body weight. One week before the Resovist-enhanced MR imaging study 20 patients underwent Gd-DTPA-enhanced MR imaging. RESULTS: Detection rate was improved for metastatic lesions revealing 36 lesions unenhanced versus 53 focal lesions using Resovist-enhanced MR imaging. Gadolinium-DTPA-enhanced scans showed no additional lesion versus unenhanced and Resovist-enhanced MR imaging. Static and dynamic imaging demonstrated no measurable percentage signal intensity loss (PSIL) using Resovist-enhanced MR imaging versus a percentage enhancement of 79.7% in Gd-DTPA enhanced scans. In the dynamic T2-weighted sequences, hepatocellular carcinoma nodules (n = 4) showed a rapid decrease in signal intensity starting at 44 seconds. Postinfusion of Resovist followed by a low, constant increase in signal intensity. Gadolinium-DTPA enhanced scans showed a percentage enhancement of 73.4 focal nodular hyperplasia (FNH) and hemangioma revealed a strong and early dose-dependent PSIL 44 to 60 seconds postinfusion with a prolonged signal loss for the FNH in the late study. Statistical evaluation revealed a statistically significant superiority of Resovist-enhanced MR imaging concerning the detection and delineation of focal liver lesions compared with unenhanced and Gd-DTPA enhanced scans (P < 0.05). CONCLUSIONS: The fast infusion of the new superparamagnetic contrast agent Resovist shows advantages for dynamic and static MR imaging of focal liver lesions.

Carcinoma, Hepatocellular↗
PubMed1996

Superparamagnetic iron oxide--enhanced versus gadolinium-enhanced MR imaging for differential diagnosis of focal liver lesions.

PURPOSE: To assess AMI-25- versus gadolinium-enhanced magnetic resonance (MR) imaging in the differential diagnosis of liver tumors. MATERIALS AND METHODS: Twenty-nine patients with liver tumors underwent unenhanced, AMI-25-enhanced (15 micromol/kg), and gadolinium-enhanced(0.1 mmol/kg) imaging within 2 weeks. RESULTS: A significant (P< .05) difference in percentage signal intensity loss (PSIL) was seen in benign tumors on AMI-25-enhanced proton-density-weighted images (nine focal nodular hyperplasia [FNH], 41%; one adenoma, 32.4%) versus malignant tumors. Gadolinium-enhanced T1-weighted gradient-echo images showed strong enhancement in benign lesions (seven FNH, 147.5%; one adenoma, 91.3%) and moderate enhancement in malignant tumors (eight hepatocellular carcinomas, 116.2%, 11 metastases, 39.7%). Receiver operating characteristic analysis revealed a threshold PSIL of 10% on AMI-25-enhanced images as the most essential criteria to distinguish benign from malignant lesions (sensitivity, 88%; specificity. 89%). Interobserver analysis for two observers revealed specificity of 93% for AMI-25-enhanced imaging versus 81.5% for gadolinium-enhanced MR imaging. CONCLUSION: AMI-25 decreased the SI of benign tumors and helped differentiate benign from malignant tumors.

Adenoma↗
PubMed1996

Liver tumors: comparison of MR imaging with Gd-EOB-DTPA and Gd-DTPA.

PURPOSE: To compare the usefulness of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) and gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) in the diagnosis of focal liver lesions. MATERIALS AND METHODS: Thirty-one patients with focal liver lesions underwent T2- and T1-weighted spin-echo magnetic resonance (MR) imaging and fast low-angle shot two-dimensional MR imaging before, during, and after intravenous administration of three different doses of Gd-EOB-DTPA (12.5, 25, and 50 mumol per kilogram body weight). Gd-DTPA-enhanced imaging (dose, 0.1 mmol per kilogram body weight) was performed in the same patients within 1 week of Gd-EOB-DTPA imaging. RESULTS: During the perfusion phase (the 3 minutes after injection of contrast material), the dynamic enhancement characteristics seen after injection of 25 and 50 mumol of Gd-EOB-DTPA were similar to those seen with Gd-DTPA. At the lowest dose of Gd-EOB-DTPA (12.5 mumol), the dynamic enhancement characteristics were not comparable to those seen with Gd-DTPA. During the hepatobiliary phase (1.5 minutes to 4 hours after injection), Gd-EOB-DTPA-enhanced images yielded a dose-independent, statistically significant improvement in the detection rate of additional metastases, hepatocellular carcinomas, and hemangiomas compared with unenhanced and Gd-DTPA-enhanced images (P < .05). CONCLUSION: Gd-EOB-DTPA-enhanced MR imaging enables improved detection of hepatic lesions over Gd-DTPA-enhanced MR imaging while providing comparable differential diagnostic information.

Adult↗
PubMed1995

Involvement of the GTP binding protein Rho in constitutive endocytosis in Xenopus laevis oocytes.

To study an endocytotic role of the GTP-binding protein RhoA in Xenopus oocytes, we have monitored changes in the surface expression of sodium pumps, the surface area of the oocyte and the uptake of the fluid-phase marker inulin. Xenopus oocytes possess intracellular sodium pumps that are continuously exchanged for surface sodium pumps by constitutive endo- and exocytosis. Injection of Clostridium botulinum C3 exoenzyme, which inactivates Rho by ADP-ribosylation, induced a redistribution of virtually all intracellular sodium pumps to the plasma membrane and increased the surface area of the oocytes. The identical effects were caused by injection of ADP-ribosylated recombinant RhoA into oocytes. The C3 exoenzyme acts by blocking constitutive endocytosis in oocytes, as determined using a mAb to the beta 1 subunit of the mouse sodium pump as a reporter molecule and oocytes expressing heterologous sodium pumps. In contrast, an increase in endocytosis and a decrease in the surface area was induced by injection of recombinant Val14-RhoA protein or Val14-rhoA cRNA. PMA stimulated sodium pump endocytosis, an effect that was blocked by a specific inhibitor of protein kinase C (Gö 16) or by ADP-ribosylation of Rho by C3. Similarly, the phorbol ester-induced increase in fluid-phase endocytosis in oocytes was inhibited by Gö 16, C3 transferase, or by injection of ADP-ribosylated RhoA. In contrast to C3 transferase, C. botulinum C2 transferase, which ADP-ribosylates actin, had no effect on sodium pump endocytosis or PMA-stimulated fluid-phase endocytosis. The data suggests that RhoA is an essential component of a presumably clathrin-independent endocytic pathway in Xenopus oocytes which can be regulated by protein kinase C.

ADP Ribose Transferases↗
PubMed1995

All-trans beta-carotene preferentially accumulates in human chylomicrons and very low density lipoproteins compared with the 9-cis geometrical isomer.

Following ingestion of a beta-carotene isomer mixture (Betatene) containing nearly equal amounts of all-trans and 9-cis beta-carotene (all-trans/9-cis beta-carotene ratio approximately 1.5), concentrations of all-trans beta-carotene increased for 6 or 8 h in the chylomicron fraction of plasma from four of seven human subjects. A substantially lower increase in the 9-cis beta-carotene concentration was observed, with the accumulation of the all-trans isomer being 10- to 50-fold higher than that of the 9-cis isomer, calculated on the basis of the beta-carotene isomer pattern in the ingested mixture. A similar effect was observed in the VLDL fraction. Three of the seven subjects did not respond to beta-carotene ingestion. In the subjects that did respond, the all-trans/9-cis beta-carotene ratios in chylomicrons and VLDL suggest an efficient isomer-selective mechanism for intestinal uptake across the mucosa or very rapid elimination into tissues.

Administration, Oral↗
PubMed1995

Relationship between flanker identifiability and compatibility effect.

What is the relation between the identifiability of masked flankers and their ability to induce compatibility effects in a letter classification task? Using a within-subjects design (n = 8), we first determined identification performance for two flankers (H or N) around an irrelevant target letter as a function of the time (stimulus onset asynchrony, or SOA) after which the flankers were masked. In a second condition, subjects classified the central letter of the same stimulus patterns irrespectively of the identity of the flankers. The compatibility effects increased with increasing identification performance as a function of SOA, and we found a significant compatibility effect even at an SOA at which the identifiability of the flankers did not differ significantly from zero. We discuss the statistical power of our design and an interpretation of our results in terms of a dissociation between perceptual processes and processes directly activating the motor system (direct parameter specification; cf. Neumann, 1990).

Adult↗
PubMed1994

Coactivation and statistical facilitation in the detection of lines.

The redundant-signals effect describes the general phenomenon that simple reaction times to two simultaneously presented signals are typically faster than the corresponding reaction times to each of the signals presented alone. Recent studies (eg Miller 1982, 1986) indicate that models of probability summation in which an independent detection of both signals is assumed cannot completely account for the observed shortening of the reaction times. Therefore, models in which some kind of coactivation is assumed are often considered as an alternative explanation. In the present study simple reaction times to parallel lines are compared with those to orthogonal lines and single lines. Our first hypothesis is that because of the redundant-signals effect, the reaction time to configurations consisting of two lines (either parallel or orthogonal) will generally be faster than the reaction time to a single line. Furthermore, line detection can be related to orientation-specific line detectors. Therefore, parallel lines may be thought to activate similar line detectors and, by coactivation, facilitate detection. As our second hypothesis we thus expect that the reaction time to parallel lines will be shorter than the reaction time to orthogonal lines. To test these hypotheses, we conducted a simple reaction-time experiment in which signal onset asynchronies ranging from 0 to +/- 56 ms for the orthogonal lines were used. In addition, reaction times to parallel lines and single lines were measured. Both hypotheses are supported by our data. We formulate a stochastic model which is able to explain both statistical facilitation and coactivation in a physiologically plausible way.

Adult↗