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Biomedical subjects

S Friedrich

Publications and source records attributed to S Friedrich.

33 records · Page 2Linked to original sources
PubMed1994

Expression of capsular polysaccharide determines serum resistance in Escherichia coli K92.

The amount of capsular polysaccharide expression has been shown to be the major determinant of serum resistance in Escherichia coli K1. E. coli K92, like K1, is a polymer of sialic acid molecules. It differs from K1 by containing both alpha (2.8) and alpha (2.9) linkages. Four strains of E. coli K92 were tested for serum resistance. Three strains were serum-resistant (50% normal human serum), one strain was moderately serum-sensitive. The serum-resistant strains expressed significantly more capsular polysaccharide than did the serum-sensitive strain. For each of the serum-resistant strains, six mutants were isolated by selection for resistance against infection with a K92-specific bacteriophage. All of the mutants expressed less capsular polysaccharide than the respective wild-type strains. All mutants were more sensitive to serum killing than the wild-type strains. In all groups, the mutants with lowest expression of capsular polysaccharide were highly serum-sensitive. Changes of outer membrane proteins or lipopolysaccharide patterns that were present in some mutants did not correlate with serum resistance properties of the mutants. Furthermore, it was investigated whether the presence of active serum had an influence on capsule expression. In the serum-sensitive strain, the presence of serum induced a significant and concentration-dependent increase of capsule expression. Serum had no effect on capsule expression by the serum-resistant strains. We conclude from the data that the expression of K92 capsular polysaccharide determines serum resistance in the strains examined.

Bacterial Capsules↗
PubMed1993

The dipole density plot (DDP), a technique to show concentrations of dipoles.

To analyse spontaneous multichannel slow-wave MEG activity a tool was developed to extract focal abnormal activity with a higher spatial dipole density across time. The first version works on discrete volume units, the second version avoids a possible location error, works continuously and can be adjusted for individual slices three-dimensionally. The first version is used for screening and the second version is used to go into more detail. The dipole density plot (DDP) is not limited to single foci, nor to the single-dipole model; neither is it limited to the MEG. The DDP seems to be a valuable tool for detecting and locating lesions three-dimensionally within the brain.

Brain Diseases↗
PubMed1992

Functional 3D localization of cerebrovascular accidents by magnetoencephalography (MEG).

Spontaneous magnetic slow wave brain activity can be used to locate the underlying sources with sufficient accuracy by using the single current dipole model. To locate focal sources from spontaneous activity a tool had to be developed to extract focal densities of dipoles across time-the dipole density plot. The first version works on discrete volume units and is used for screening. The second version avoids a possible localization error and works continuously and this even is done on individual slices. The DDP seems to be a valuable tool for extracting and separating different focal sources from the background activity. Not only brain infarctions and haemorrhages (and cysts and angiomas) could be located, but also functional sources associated with TIAs even one week after the symptoms. First results let us assume that clinically silent TIAs also (in analogy to clinically silent brain infarctions) could be detected and located.

Brain↗
PubMed1990

[An occurrence of a neurogenic sarcoma in an irradiated field following the combined surgical-radiologic treatment of a childhood adenosarcoma of the kidney].

Malignant neoplasias in childhood generally are an increased risk for the patient to fall ill with a second tumor. Second tumors in former irradiation field are seldom, but are acknowledged radiogenically if histology is different to that of the first tumor and a sufficiently long period is between the two tumors. A patient is represented who had been operated and irradiated because of an adenosarcoma of the kidney at the age of seven and who has fallen ill with a neurogenic sarcoma in irradiation area more than 30 years later. The same patient had to suffer from radiogenic retardation during differentiation of lumbar apparatus of attitude and locomotion and on the other hand he became father of a healthy daughter at the age of 32.

Child↗
PubMedDate not supplied

Finite element modeling of drug distribution in the vitreous humor of the rabbit eye.

Direct intravitreal injection of drug is a common method for treating diseases of the retina or vitreous. The stagnant nature of the vitreous humor and surrounding tissue barriers creates concentration gradients within the vitreous that must be accounted for when developing drug therapy. The objective of this research was to study drug distribution in the vitreous humor of the rabbit eye after an intravitreal injection, using a finite element model. Fluorescein and fluorescein glucuronide were selected as model compounds due to available experimental data. All required model parameters were known except for the permeability of these compounds through the retina, which was determined by fitting model predictions to experimental data. The location of the intravitreal injection in the experimental studies was not precisely known; therefore, several injection locations were considered, and best-fit retinal permeability was determined for each case. Retinal permeability of fluorescein and fluorescein glucuronide estimated by the model ranged from 1.94 x 10(-5) to 3.5 x 10(-5) cm s(-1) and from 0 to 7.62 x 10(-7) cm s(-1), respectively, depending on the assumed site of the injection. These permeability values were compared with values previously calculated from other models, and the limitations of the models are discussed. Intravitreal injection position was found to be an important variable that must be controlled in both experimental and clinical settings.

Algorithms↗
PubMedDate not supplied

Retention behavior of humic substances in reversed phase HPLC.

Recovery as well as appearance and abundance (in percent) of different fractions of humic substances are found to depend on injected sample amounts in reversed phase HPLC. Sample amounts have been varied both by varying sample concentration and sample volume. In case of lowest amounts injected only two fractions were obtained for a commercial humic acid sodium salt, i.e. one for excluded molecules and one for hydrophobic components. The abundance of excluded molecules decreases upon increasing amounts injected. Another three fractions are obtained upon increasing amount injected: a hydrophilic fraction and two hydrophobic ones. This behavior is explained by auxiliary equilibria between excluded components and humic molecules previously adsorbed on the stationary phase.

Journal Article↗