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Biomedical subjects

H-W Müller

Publications and source records attributed to H-W Müller.

11 recordsLinked to original sources
PubMed2006

[Tissue engineering of peripheral nerves].

BACKGROUND: In spite of considerable progress in microsurgical techniques, the treatment of long distance defects in peripheral nerves remains challenging for the surgeon. Autologous nerve grafting has been the only applicable procedure to overcome such defects in the past. Due to the known disadvantages of this procedure (neuroma formation and sensory deficits at the donor-site, limited availability of donor-material, etc.) and impaired regenerative results, different tubulisation techniques are discussed more frequently as alternatives to the autologous nerve grafts. AIM OF THE STUDY: In this work, the authors summarise their experiences and results with different synthetically developed materials, cellular and acellular tubes and venous conduits for the reconstruction of peripheral nerve defects. MATERIAL AND METHODS: To analyse peripheral nerve regeneration, we utilised a median nerve model in rats. In these studies nerve gaps up to 40 mm were induced. Guiding tubes of various materials (trimethylene carbonate-epsilon-caprolactone, polyethylene, veins, and collagen) were employed. Furthermore, we introduced Schwann cells as cellular elements into some of the trimethylene carbonate-epsilon-caprolactone tubes. The longest postoperative observation period was nine months. RESULTS: The results demonstrated that only in the case of cellular filled tubes (syngenic Schwann cells) did regeneration occur across the 20 mm gap. This regeneration was comparable to that induced after autologous grafting. Across a 40 mm gap the autologous graft demonstrated the best results.

Animals↗
PubMed2006

[Localisation of parathyroid glands using planar (99m)Tc-sestamibi scintigraphy. Comparison between subtraction- and dual-phase technique].

AIM: In the context of presurgical localisation of parathyroid adenomas in primary hyper-parathyreoidism (pHPT) using (99m)Tc-sestamibi scintigraphy, subtraction- and dualphase technique are compared with each other and with the surgical findings. PATIENTS, METHODS: Prospectively, 126 patients with pHPT were investigated presurgically. For visualisation of parathyroid adenomas, an image of the thyroid ((99m)Tc-pertechnetat) was subtracted from a perfusion image ((99m)Tc-sestamibi) and 2 h p. i. another image was acquired for identification of retention of activity. Considering both techniques the clinical findings were reported promptly. Retrospectively, the evaluations were presented separately to four experienced raters. RESULTS: In clinical routine for 109 patients correct findings were reported presurgically (87%). From 129 resected parathyroid adenomas 118 were localised correctly (sensitivity 91%, positive predictive value 94%). Concerning the retrospective analysis, in 75% of the cases both techniques provided the correct site, in 14% only the dual-phase technique and in 7% only the subtraction-technique was correct. With the help of the dual-phase technique significantly more investigations were correctly rated than with the help of the subtraction technique (88.7 +/- 3.2% vs. 81.6 +/- 1.2%, p < 0.01, two-sided t-test). CONCLUSION: The presurgical scintigraphic localisation of hyperactive parathyroid glands in pHPT assists minimal invasive surgery serving a high rate of correct findings. According to our data the dual-phase technique seems to be more sensitive than the subtraction technique. In some cases, however, the correct site may only be found using the subtraction technique. For an optimal surgical strategy we suggest the combination of both techniques.

Humans↗
PubMed2005

RNA interference-based strategies for metabolic syndrome treatment.

RNA interference is a naturally occurring cellular mechanism to inhibit the expression of specific gene products. The technical application of RNA interference offers great potential for the specific treatment of a huge variety of diseases including the metabolic syndrome, one of the most challenging threats to human health associated with our civilization. In order to develop novel and powerful strategies for the treatment of the metabolic syndrome, it is essential to define a set of specific gene products that may be targeted by RNA interference. Based on currently available in vitro and in vivo data, we discuss the feasibility of candidate genes involved in the pathophysiology of the metabolic syndrome as potential targets for a rational RNA interference based therapy in this review.

Animals↗
PubMed2005

Myocardial perfusion/metabolism mismatch and ventricular arrhythmias in the chronic post infarction state.

AIM: Ventricular arrhythmias have been shown to originate in the myocardial peri-infarct region due to irregular heterotopic conduction. Hypoperfused but viable myocardium is often localised in those areas and may be involved in the pathogenesis of arrhythmias. We tested the hypothesis that these myocardial perfusion/metabolism mismatches (MM) are significantly associated with ventricular arrhythmias in the chronic post infarction state. PATIENTS, METHODS: 47 post infarction patients were included in the study. 33 suffered from ventricular arrhythmia whereas 14 did not. All patients underwent (99m)Tc tetrofosmin SPECT and (18)F-FDG PET. A region-of-interest(ROI)-analysis was used to assess viable myocardium based on predefined MM-criteria. Univariate analyses as well as a logistic regression model for the multivariate analysis were carried out. RESULTS: 94% of the arrhythmic patients displayed at least one MM-segment as compared to 64% of the non-arrhythmic patients. MM-segments and arrhythmia showed a statistically significant relation (p = 0.018). The logistic regression model predicted the occurrence or absence of arrhythmia in 85% of all cases. Multivariate analysis gave consistent results, after adjusting for symptomatic chronic heart failure (CHF), aneurysms and age. CONCLUSION: Our results support the hypothesis that hypoperfused but viable myocardium represents an arrhythmogenic substrate and is a relevant risk factor for developing ventricular arrhythmias following myocardial infarction. Therefore, the detection of MM-segments allows the identification of patients with a higher risk for future cardiac events.

Coronary Disease↗
PubMed2005

[State-of-the-art of small animal imaging with high-resolution SPECT].

During the recent years, in vivo imaging of small animals using SPECT has become of growing relevance. Along with the development of dedicated high-resolution small animal SPECT cameras, an increasing number of conventional clinical scanners has been equipped with single or multipinhole collimators. This paper reviews the small animal tomographs, which are operating at present and compares their performance characteristics. Furthermore, we describe the in vivo imaging studies, which have been performed so far with the individual scanners and survey current approaches to optimize molecular imaging with small animal SPECT.

Animals↗
PubMed2004

Dissociating neural correlates for nouns and verbs.

Dissociations in the ability to produce words of different grammatical categories are well established in neuropsychology but have not been corroborated fully with evidence from brain imaging. Here we report on a PET study designed to reveal the anatomical correlates of grammatical processes involving nouns and verbs. German-speaking subjects were asked to produce either plural and singular nouns, or first-person plural and singular verbs. Verbs, relative to nouns, activated a left frontal cortical network, while the opposite contrast (nouns-verbs) showed greater activation in temporal regions bilaterally. Similar patterns emerged when subjects performed the task with pseudowords used as nouns or as verbs. These results converge with findings from lesion studies and suggest that grammatical category is an important dimension of organization for knowledge of language in the brain.

Adult↗
PubMed2004

Depression and anxiety in different thyroid function states.

Previous studies on hypothyroid subjects have indicated serious psychiatric symptoms affecting the patients' quality of life. The present prospective cross-sectional study's aim was to examine these symptoms in thyroid patients with different functional states. A total of 254 patients (age: 56 +/- 14 years [mean +/- standard deviation], 181 female, 73 male) referred to a hospital for radioiodine treatment of hyperthyroidism or for follow-up of differentiated thyroid cancer, respectively, were included. All patients underwent the twelve-item general health questionnaire, which is an instrument for detecting mood disturbances. Euthyroid and hyperthyroid patients did not differ significantly in their general health questionnaire score (11 +/- 5 vs. 11 +/- 7), nor did subclinical hyperthyroid (11 +/- 6) or subclinical hypothyroid subjects (12 +/- 5). In contrast, hypothyroid patients showed a significantly higher mean score (17 +/- 7, p < 0.001, ANOVA). Binary logistic regression revealed that hypothyroidism increases age and gender-adjusted risk for critical mood deterioration by seven-fold. Thus, hypothyroidism represents a widely underestimated functional condition that may severely affect mental health.

Adult↗
PubMed2003

Pattern formation at the bicritical point of the Faraday instability.

We present measurements on parametrically driven surface waves (Faraday waves) performed in the vicinity of a bicritical point in parameter space, where modes with harmonic and subharmonic time dependence interact. The primary patterns are squares in the subharmonic and hexagons in the harmonic regime. If the primary instability is harmonic we observe a hysteretic secondary transition from hexagons to squares without a perceptible variation of the fundamental wavelength. The transition is understood in terms of a set of coupled Landau equations and related to other canonical examples of phase transitions in nonlinear dissipative systems. Moreover, the subharmonic-harmonic mode competition gives rise to a variety of new superlattice states. These structures are interpreted as mediator modes involved in the transition between patterns of fourfold and sixfold rotational symmetry.

Journal Article↗
PubMed2003

Hydrodynamics of isotropic ferrogels.

We derive the complete set of macroscopic dynamic equations for ferrogels under an external magnetic field, including the magnetization as an independent dynamic degree of freedom. The magnetoelasticity comes in the form of magnetostriction and through the magnetic part of the Maxwell stress. Various dynamic couplings of the elastic degree of freedom with the magnetization and the magnetic field are found. We discuss static elongation, shear deformations, and the modified sound spectrum in the presence of an external magnetic field.

Journal Article↗
PubMed2003

[Neurocognition and PET. Strategies for data analysis in activation studies on working memory].

AIM: In cognitive neuroscience regional cerebral blood flow (rCBF) imaging with positron-emission-tomography (PET) is a powerful tool to characterize different aspects of cognitive processes by using different data analysis approaches. By use of an n-back verbal working memory task (varied from 0- to 3-back) we present cognitive subtraction analysis as basic strategy as well as parametric and covariance analyses and discuss the results. METHODS: Correlation analyses were performed using the individual performance rate as an external covariate, computing inter-regional correlations, and as network analysis applying structural equation modelling to evaluate the effective connectivity between the involved brain regions. RESULTS: Subtraction analyses revealed a fronto-parietal neuronal network also including the anterior cingulate cortex and the cerebellum. With higher memory load the parametric analysis evidenced linear rCBF increases in prefrontal, pre-motor and inferior parietal areas including the precuneus as well as in the anterior cingulate cortex. The rCBF correlation with the individual performance as external covariate depicted negative correlations in bilateral prefrontal and inferior parietal regions, in the precuneus and the anterior cingulate cortex. The network analysis demonstrated mainly occipito-frontally directed interactions which were predominantly left-hemispheric. Additionally, strong linkages were found between extrastriate and parietal regions as well as within the parietal cortex. CONCLUSION: The data analysis approaches presented here contribute to an extended and more elaborated understanding of cognitive processes and their different sub-aspects.

Brain↗