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Biomedical subjects

R Friedrich

Publications and source records attributed to R Friedrich.

At least 37 records · Page 2Linked to original sources
PubMed1999

Loss of NF1 allele in Schwann cells but not in fibroblasts derived from an NF1-associated neurofibroma.

Neurofibromas, the hallmark of neurofibromatosis 1, are composed mainly of Schwann cells and fibroblasts. Inactivation of both NF1 alleles is the cause of these benign tumors, but it is unknown which cell type is the progenitor. In this study, we selectively cultured Schwann cells from an NF1-associated neurofibroma. Fibroblasts were also obtained by culturing the tumor cells under standard conditions. Using four intragenic markers, we genotyped the NF1 locus in the original tumor and in the derived Schwann cells and fibroblasts. Loss of heterozygosity for two informative markers, which indicates loss of one NF1 allele, was found in Schwann cells but not in fibroblasts. This result suggests that genetic alterations of the NF1 gene in Schwann cells are responsible for the development of neurofibromas.

Alleles↗
PubMed1999

Analysis of spatiotemporal signals: a method based on perturbation theory.

We present a method of analyzing spatiotemporal signals with respect to its underlying dynamics. The algorithm aims at the determination of spatial modes and a criterion for the number of interacting modes. Simultaneously, a way of filtering of nonorthogonal noise is shown. The method is discussed by examples of simulated stable fixpoints and the Lorenz attractor.

Journal Article↗
PubMed1998

Monitoring of microhemodynamic changes during ex vivo xenogeneic liver perfusion using intravital microscopy.

The main targets of xenogeneic rejection mechanisms are the endothelial cells of the graft. Their activation and the consequent alteration of the organ's microcirculation lead to the destruction of the xenograft. Microhemodynamic changes occurring during this process are still poorly characterized. The aim of this study was to analyze the microcirculation during xenogeneic ex vivo hemoperfusion of rat livers and to monitor the impact of treatment strategies using intravital fluorescence microscopy. In contrast to the isogeneic control group, blood flow almost completely stopped within the first minutes of xenoperfusion. Simultaneously, perfusion pressure increased and bile production was reduced. Acetylsalicylate (Aspisol) and the platelet-activating factor antagonist WEB 2170 improved the microcirculation and function of the xenoperfused liver. The combination showed a synergistic effect. After apheresis of preformed xenogeneic antibodies, the parameters measured were comparable with those seen in isogeneic experiments. Complement degradation with cobra venom factor revealed a minor improvement in perfusion. A rapid, extensive, and irreversible leukocyte accumulation in terminal portal vessels was observed in all xenogeneic experiments. Blood counts of the perfusate confirmed the early trapping of leukocytes and platelets in the xenoperfused liver, indicating nonimmunological, cellular involvement in this rejection process.

Animals↗
PubMed1998

Health risks of energy systems.

Health risks from fossil, renewable and nuclear reference energy systems are estimated following a detailed impact pathway approach. Using a set of appropriate air quality models and exposure-effect functions derived from the recent epidemiological literature, a methodological framework for risk assessment has been established and consistently applied across the different energy systems, including the analysis of consequences from a major nuclear accident. A wide range of health impacts resulting from increased air pollution and ionizing radiation is quantified, and the transferability of results derived from specific power plants to a more general context is discussed.

Air Pollution↗
PubMed1996

Role of epinephrine-induced hypokalemia in the regulation of renin and aldosterone in humans.

Circulating epinephrine induces both stimulation of plasma renin activity (PRA) and a decrease in serum potassium concentration. This study was designed to determine the dose-response effects of systemic epinephrine infusion on the relationship of PRA and plasma aldosterone concentration. Twenty-one men with normal blood pressure received either an intravenous infusion of epinephrine at 12.5, 25, and 50 ng/(kg x min) by stepwise increments for 1 hour each or isotonic saline solution. Infusion of epinephrine led to a dose-dependent increase in plasma epinephrine concentration, systolic blood pressure, and heart rate, whereas diastolic blood pressure was decreased. PRA was elevated in a dose-dependent manner, whereas the plasma aldosterone concentration was reduced. During infusion of epinephrine, the serum potassium concentration and renal potassium excretion were significantly decreased. We conclude that despite marked stimulation of PRA, the plasma aldosterone concentration was further decreased because of a dose-dependent decrease in serum potassium concentration induced by epinephrine. Thus hypokalemia appears to be the predominant regulator of plasma aldosterone during incremental epinephrine infusion.

Adult↗
PubMed1996

Substance P and calcitonin gene-related peptide in the chicken skin: distribution and cardiovascular effects.

A short vasodilatation but no plasma extravasation could be induced by antidromic stimulation of peripheral nerves in the chicken skin. Since in mammalian species the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) are involved in this mechanism, the distribution and the cardiovascular effect of these peptides were investigated in the chicken. In the skin, SP- and CGRP-immunoreactivity was found co-localized in the epidermis and dermis. On blood vessels, however, SP positive but CGRP negative nerve rfibres were observed. Systemic (i.v.) and local close arterial injection of SP produced dose-dependent cutaneous vasodilatation with threshold doses of 6.5 pmol/kg or 1 pmol, respectively. Neurokinin A and acetylcholine were about 20 to 50-fold less effective, when injected close arterially. Systemic injection of SP (5-1800 pmol/kg) dose-dependently evoked a short fall in blood pressure which was followed by a longer lasting pressor response. CGRP up to 800 pmol/kg did not change blood pressure but produced a pronounced tachycardia. Close arterial injection of CGRP resulted in variable bi- or triphasic vascular responses which consisted of vasodilatations and also vasoconstriction with thresholds between 0.25 and 65 pmol. The data also indicate that in the chicken, SP, and to a lesser extent CGRP, can be involved in antidromic vasodilatation.

Acetylcholine↗
PubMed1996

[Mandibular collum fracture in the ultrasound image--indications and limits from the viewpoint of 3 years imaging experiences].

The Ultrasound technique as an image producing procedure for fractures of the mandibular collum is outlined with physical theory and clinical examples. Advantages and disadvantages are compared and it is stated that a part of all patients with fractures might have a benefit from this method. Mentally handicapped patients, pregnant women and all sorts of fidgety patients will profit by the ultrasound investigation as the only way to ascertain the bone-fracture. There is necessity to relate the sonogram to a conventional X-ray picture whenever it is possible, for the procedure is suited to prove the fracture, not to exclude it.

Adolescent↗
PubMed1995

The prognostic value of DNA ploidy and S-phase estimate in primary breast cancer: a prospective study.

In this prospective study, the independent prognostic value of DNA ploidy in combination with the major clinico-pathological characteristics (histological grade, nodal status, tumor size, estrogen and progesterone receptor status, number of tumors, multicentricity, lympho-vascular infiltration) was evaluated in a series of 399 breast-cancer patients. The mean follow-up time was 4.5 years. The DNA content was measured using image cytometry on fresh tumor samples. The overall survival of tetraploid and slowly proliferating diploid cases was significantly different compared with that of aneuploid and rapidly proliferating diploid cases (p = 0.0002). Thus, DNA ploidy combined with S-phase estimate (DNA histogram type) appeared to be good prognostic factors. In a multivariate survival analysis, DNA histogram type was not an independent prognostic factor unless the histological grade was excluded. This effect of DNA histogram type on survival was also observed among patients with grade-I or -II tumors and patients with small tumors. In conclusion, DNA histogram type was a valuable prognostic factor in univariate analysis, and provided independent complementary information for patients considered at low or intermediate risk by classical pathological findings.

Adenocarcinoma↗
PubMed1995

[A comparison of NMR tomography and arthrography in functional disorders of the temporomandibular joint].

PATIENTS AND METHODS: 31 patients with clinically diagnosed dysfunction of the temporomandibular joint (TMJ) were examined by magnetic resonance imaging (MRI; 1.5 Tesla, TR/TE 600/30) in closed and open mouth position and functional arthrography with digital image recording. RESULTS: Both methods agreed in the evaluation of the disc position. In 23 joints with displaced disc reposition was found in 11 cases and in 14 cases using MRI or arthrography, respectively. MRI proved to be superior in the diagnosis of sideways disc rotations. Joint hypermobility, eccentric disc displacement (n = 4) and perforation (n = 3) were shown by functional arthrography. Due to the good demonstration of osseous, muscular and discoligamentous structures, MRI as a noninvasive imaging modality is the method of choice for TMJ evaluation. Arthrography can be advantageous in complex functional disturbances or if MRI and clinical findings are inconclusive. The clinical diagnosis of disc displacement was found to be accurate in only 68% of the cases.

Adolescent↗
PubMed1994

A theoretical model of phase transitions in the human brain.

An experiment using a multisensor SQUID (superconducting quantum interference device) array was performed by Kelso and colleagues (1992) which combined information from three different sources: perception, motor response, and brain signals. When an acoustic stimulus frequency is changed systematically, a spontaneous transition in coordination occurs at a critical frequency in both motor behavior and brain signals. Qualitatively analogous transitions are known for physical and biological systems such as changes in the coordination of human hand movements (Kelso 1981, 1984). In this paper we develop a theoretical model based on methods from the interdisciplinary field of synergetics (Haken 1983, 1987) and nonlinear oscillator theory that reproduces the main experimental features very well and suggests a formulation of a fundamental biophysical coupling.

Acoustic Stimulation↗
PubMed1994

Use of superoxide dismutase (SOD) in patients with temporomandibular joint dysfunction--a preliminary study.

The aim of this preliminary study was to investigate and assess the effect of intra-articular injection of superoxide dismutase (SOD) in patients with temporomandibular joint (TMJ) dysfunction who had not responded to conservative therapy in a first study. Thirty joints in 29 patients were studied. The results showed that intra-articular injection of superoxide dismutase was effective in 25 joints (83%). It was concluded that intra-articular injection of superoxide dismutase may be an alternative therapy for patients with TMJ dysfunction who fail to respond to conservative treatment.

Adult↗
PubMed1994

[Merkel cell carcinoma of the face. Histology, clinical course and therapy in six cases].

Six patients suffering from Merkel cell carcinoma of the face are described. A reliable confirmation and differential diagnosis of Merkel cell carcinoma have become possible with the aid of immunohistochemistry. There is a poor prognosis for patients affected by this tumour. Three out of the six cases described died within two years, two of them with distant metastases, one with a widespread local recurrence. Optimal treatment of Merkel cell carcinoma consists in early radical resection, perhaps combined with radiotherapy.

Aged↗