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Biomedical subjects

V Schmidt

Publications and source records attributed to V Schmidt.

At least 19 recordsLinked to original sources
PubMed2002

Intercomparison exercise of the PTB, BfS, MPA and PSI calibration facilities for radon gas concentration.

The traceability chain of one national reference laboratory (PTB) and three accredited radon calibration laboratories (BfS MPA and PSI) to internationally acknowledged radon gas standards is specified. As an additional tool for quality assurance, interchange of an electronic radon measuring instrument was used as a means for a relative comparison of the radon gas reference atmospheres. The instrument was exposed to radon gas activity concentrations between 500 Bq.m(-3) and 15 kBq.m(-3). Measured sensitivities of the participants agree well inside the range of specified calibration uncertainties.

Calibration↗
PubMed2001

Measurements of deposition velocity of radon decay products for examination of the correlation between air activity concentration of radon and the accumulated Po-210 surface activity.

The retrospective determination of radon exposure levels in dwellings by means of the measurement of the Po-210 surface activity is subject to various uncertainties. These result partly from the values assumed for the equilibrium factor F and for the unattached fraction f(p), and, more importantly, from differences in the deposition velocities of short-lived decay products of Rn-222, caused by varying conditions of turbulence. In order to evaluate the actual range of the variation which occurs under German living conditions, measurements for the deposition velocity parameter were carried out in several dwellings in which increased levels of radon were present. The statistical evaluation of the measurements produced a mean deposition velocity of 1.7 m/h for Po-218 and 0.4 m/h for Pb-214, and a relative standard deviation in the measured values of as low as approximately 50%. This lay significantly below the uncertainty value expected from the literature and would seem to justify the retrospective determination of the radon exposure from Po-210 surface activity measurement for use in, for example, epidemiological studies.

Air Pollutants, Radioactive↗
PubMed2000

Dynamics of laser desorption and ablation of metals at the threshold on the femtosecond time scale

The dynamics of the laser-ablation (-desorption) process of metals (Al, Ag, Fe, and Ni) initiated by 30 fs laser pulses has been investigated by interferometric time-resolved pump-probe measurements. It is postulated that a sufficiently high density of hot electrons is essential for achieving desorption of metal ions. In addition, we have observed a new and unexpected behavior characterized by delayed ablation for a pump-probe beam delay in the range of several ps for Al, Ni, and Fe. This second peak is attributed to the development of a liquid surface layer developing after a few ps. Molecular dynamics simulations support this assumption.

Journal Article↗
PubMed2000

Classification of spatial textures in benign and cancerous glandular tissues by stereology and stochastic geometry using artificial neural networks.

Stereology and stochastic geometry can be used as auxiliary tools for diagnostic purposes in tumour pathology. Whether first-order parameters or stochastic-geometric functions are more important for the classification of the texture of biological tissues is not known. In the present study, volume and surface area per unit reference volume, the pair correlation function and the centred quadratic contact density function of epithelium were estimated in three case series of benign and malignant lesions of glandular tissues. The information provided by the latter functions was summarized by the total absolute areas between the estimated curves and their horizontal reference lines. These areas are considered as indicators of deviation of the tissue texture from a completely uncorrelated volume process and from the Boolean model with convex grains, respectively. We used both areas and the first-order parameters for the classification of cases using artificial neural networks (ANNs). Learning vector quantization and multilayer feedforward networks with backpropagation were applied as neural paradigms. Applications included distinction between mastopathy and mammary cancer (40 cases), between benign prostatic hyperplasia and prostatic cancer (70 cases) and between chronic pancreatitis and pancreatic cancer (60 cases). The same data sets were also classified with linear discriminant analysis. The stereological estimates in combination with ANNs or discriminant analysis provided high accuracy in the classification of individual cases. The question of which category of estimator is the most informative cannot be answered globally, but must be explored empirically for each specific data set. Using learning vector quantization, better results could often be obtained than by multilayer feedforward networks with backpropagation.

Breast↗
PubMed2000

Telemedicine in the control of intra-ocular pressure.

Glaucoma is one of the most common causes of blindness in the Western world and a major risk factor is increased intra-ocular pressure. We therefore used telemedicine in its control. Patients measured their intra-ocular pressure several times a day with a portable instrument and the values were then entered into a portable digital assistant. These data were transmitted by a modem to a central server. If the intra-ocular pressure was pathologically high, an email message was automatically sent to the ophthalmologist. The pressure curve, including a statistical analysis, was displayed in an easily readable chart format. Ten patients with glaucoma participated in a trial. Self-tonometry with telemedicine enabled continuous evaluation of the patient by the ophthalmologist. This approach offered the advantage of controlling the treatment remotely. Advantages for the patient were that the measurements were easily done at home under normal conditions, and the patient could control when the measurement and data transmission would be performed. Telemedicine is a cost-effective technique enabling the early diagnosis of pathologically increased intra-ocular pressure.

Glaucoma↗
PubMed2000

MedStage--platform for information and communication in healthcare.

This application report describes the technologies and strategies used by MedStage, an open infrastructure for secure telemedical internet applications. The infrastructure includes several technical and application frameworks including a public key infrastructure for providing professional security solutions, like certificate-based authentication, secure transport protocol, strong data encryption and digital signature. The key components are an universal healthcare data repository based on the work of CEN TC 251 with extensions for the storage of multimedia data, an exchangeable authorization management, an exchangeable patient index service based on CORBAmed PIDS and a set of XML-based import and export modules. Additionally there are prototype applications for home-monitoring, telereporting and personal health passport.

Computer Communication Networks↗
PubMed1999

Pontine axonal injury after brain trauma and nontraumatic hypoxic-ischemic brain damage.

Experimental studies have shown that diffuse axonal injury is usually induced by positive or negative acceleration mechanisms. In order to determine the reliability of axonal injury (AI) as a marker of this type of traumatic insult, we compared cases of trauma-induced focal cortical hemorrhage without dural involvement (n = 67) with cases of trauma-induced subdural bleeding without cortical hemorrhage (n = 26). Both groups exhibited a wide range of post-traumatic survival times. The injuries in the first group were caused mainly by direct impact to the head, those in the second by acceleration/deceleration mechanisms. The investigations were based primarily on immunohistochemical demonstration of antibodies targeted to beta-amyloid precursor protein (beta-APP) in the pons as a marker of AI and the results were assessed semiquantitatively. No significant differences were found between the two groups. In both groups AI was detected in 80-100% of cases with survival times of more than 3 h and two thirds of all positive cases showed pronounced positivity. Additional comparison of cases of brain death due to mechanical trauma (n = 14) with cases of brain death due to non-mechanical trauma (n = 18) also disclosed no significant intergroup differences. Finally, investigations of the pons in cases of non-traumatic death due to cerebral hypoxia/ischemia (n = 51) demonstrated AI with the same frequency as in the other groups, although the expression tended to be less pronounced. Our results confirm that beta-APP expression in the pons is a reliable indicator of AI but does not discriminate between injuries caused by traumatic strain or shearing mechanisms and secondary damage due to cerebral hypoxia/ischemia or edema. In the large majority of cases with prolonged post-traumatic survival, it can therefore be assumed that AI in the pons is the consequence of primary and/or secondary events or a combination of both, as is common in non-missile head injury survived for more than 90-120 min. Therefore, positive differentiation of the type of biomechanical event based on this criterion alone is not possible.

Adolescent↗
PubMed1999

German shepherd dog is suspected of sexually abusing a child.

A rare case of provoked anal penetration of an 11-year-old boy by a male German shepherd dog was confirmed by the results of morphological, serological and molecular genetic investigations. These results were of great importance to refute the suspicion on two adults. Some serious doubts remained in the version of the course of the event as presented by the boy. Some weeks later when confronted by a psychologist, the boy admitted having deliberately stimulated the dog manually and caused the animal to penetrate him.

Anal Canal↗
PubMed1999

Correlates of benzodiazepine abuse in methadone maintenance treatment. A 1 year prospective study in an Israeli clinic.

AIMS: This study addressed the following questions for patients after 1 year of methadone maintenance treatment (MMT); (1) What are the demographic features and past history of drug use of benzodiazepine (BZD) abusers? (2) Do BZD abusers abuse more heroin, cocaine and/or cannabis and do they receive a higher methadone dosage level? (3) Do BZD abusers suffer more from hepatitis C (HCV) and do they have more HIV/HCV risk-taking behaviors than non-abusers? (4) Do BZD abusers have more psychopathology and more emotional distress than non-abusers? DESIGN: All 148 patients who completed 1 year of MMT underwent random and twice-weekly observed urine analysis for various drugs of abuse, responded to self-report questionnaires (SCL-90-R; POMS; HIV/HCV risk-taking behaviors), interviews (ASI) and underwent testing for hepatitis C. Abuse in this study is defined as any use during the 12th month of treatment. FINDINGS: After 1 year of MMT, more BZD abusers (n = 63) were single, had spent time in prison, were unemployed and had at least one parent with an addiction problem or mental illness in comparison to non-abusers (n = 85). They had started using heroin and cocaine earlier and currently abused more cocaine, heroin and cannabis. They had significantly more psychopathology and negative mood. They had significantly more HCV and reported more HIV/HCV risk-taking behavior. IMPLICATIONS: We suggest that this group of patients is in need of more intensive pharmacological and psychological treatment.

Adult↗
PubMed1998

Axonal injury--a diagnostic tool in forensic neuropathology? A review.

We used beta-amyloid precursor protein (beta-APP) to investigate our own forensic neuropathological case material (n = 252) in light of the current literature on the phenomenon "axonal injury" (AI) to determine the incidence, specificity and biomechanical significance of AI and its significance for determining vitality and survival time. The case material consisted of cases of fatal nonmissile closed-head injury (n = 119), gunshot injury (n = 30), fatal cerebral ischemia/hypoxia (n = 51), brain death caused by mechanical trauma (n = 14) or nonmechanical injury (n = 18), and acute hemorrhagic shock (n = 20). AI was observed in 65% to 100% of cases of closed-head injury, fatal cerebral ischemia/hypoxia, and brain death with a survival time of more than 3 h; AI could not be detected in the cases of acute hemorrhagic shock. A statistically significant difference between traumatically and nontraumatically induced (nondisruptive) AI was not found. There was no statistical evidence of a correlation between AI and the different types of external force, since AI could be demonstrated after both acceleration/deceleration injuries and traumatic impact. Therefore, biomechanical inferences for reconstruction purposes are not possible. On the other hand, beta-APP was found to be a definite marker of vitality. In our material, cases with a posttraumatic interval of under 180 min did not express beta-APP. Moreover, the literature shows that the posttraumatic interval can be determined by other methods for demonstration of AI such as by ubiquitin immunostaining (360 min), silver staining (15-18 h), hematoxylin and eosin staining (about 24 h), or by demonstration of a microglial reaction (about 4 to 10 days) or of a few remaining isolated bulbs, without accompanying fibers, which can be detected after a survival time of up to 17 months.

Adolescent↗
PubMed1998

Neurohumoral cardiovascular responses to alcohol and their modulation by peroral fluid.

Reports on the physiologic effects of acute alcohol are far from uniform and probably reflect differences in study designs, which seldom or never consider the effects of coadministered volumes. We therefore measured blood pressure, heart rate, and heart rate variability (HRV) by power spectrum analysis, baroreceptor sensitivity, arterial blood flow, pulsed-wave velocity (PWV), and plasma levels of vasoactive hormones according to 2 protocols: group A = alcohol, 1 g/kg body weight, mixed with 500 ml of juice; and group B = similar to A plus 750 ml of mineral water. Each group comprised 9 healthy men, studied before and during the subsequent 1 and 1/2 hours after finishing the alcohol. In A, but not in B, alcohol increased heart rate (p = 0.01) and lowered systolic pressure (p <0.05). Plasma renin activity decreased only in B (p <0.01). Atrial natriuretic factor decreased in A, but increased in B (both p <0.02). Pancreatic polypeptide decreased (both p <0.001), and catecholamines did not change. In both groups, alcohol reduced PWV and increased blood flow. Baroreceptor sensitivity and the high-frequency band of HRV decreased in both groups. The physiologic response to acute administration of alcohol appears to depend on the volume of coadministered volumes. Alcohol further appears to interfere with vagal, rather than with sympathetic activity.

Adult↗
PubMed1998

Clinical experiences with minimally invasive mitral valve surgery using a simplified Port Access technique.

OBJECTIVE: Using the initial experiences with the Port-Access technique for the treatment of mitral valve disease some changes were made thus resulting in more simple and faster procedures. METHODS: Twenty-nine patients (13 male, 16 female, aged 30 to 75 years, median 62.5 +/- 11.0 years) underwent minimally invasive mitral valve surgery between May 1996 and December 1997. The underlying diseases were: mitral valve insufficiency (n = 16), mitral valve stenosis (n = 7) and combined mitral valve disease (n = 6). Through a small right thoracotomy (5-7 cm) access to the pericardium and the heart was gained. Cardiopulmonary bypass was instituted through femoral cannulation and an intraaortic balloon-catheter was introduced for aortic occlusion, aortic root venting and delivery of cold crystalloid cardioplegia. Mitral valve repair (five patients) or replacement (24 patients) was performed. RESULTS: There was no death during the whole follow-up period. There was no perivalvular leak and only minor residual mitral valve regurgitation was observed on intraoperative or postoperative (3 months) transesophageal echocardiography in three patients. There was no postoperative study-related complication. Time of ventilation and intensive care unit were comparable with the data of patients undergoing conventional mitral valve surgery but hospital stay was shorter in the last 10 consecutive cases. CONCLUSIONS: This simplified technique of mitral valve surgery combines the advantage of less invasive operative and good cosmetic results with the safety of conventional mitral valve surgery. At our institution this technique presents in well selected patients suffering from mitral valve disease the procedure of choice.

Cardiac Surgical Procedures↗
PubMed1997

The utility of two rodent species in carcinogenic risk assessment of pharmaceuticals in Europe.

For the past 20-30 years, lifespan carcinogenicity studies for pharmaceuticals have been required to be carried out in two rodent species. Due to scientific progress, the necessity/justification of lifespan studies in two species for the assessment of carcinogenic risk of pharmaceuticals is currently under discussion. A study in one species (either rat or mouse) might suffice. To appraise the need for a study in a second species, a database was compiled of all pharmaceuticals tested for carcinogenicity for which a marketing authorization was applied for in Germany and The Netherlands since 1980. The incidence of treatment-related tumor findings was determined in either rat or mouse or in both. Tumor findings occurred for nearly 50% of all compounds, with the rat being more sensitive than the mouse. Specific attention was given to the question whether tumor findings in mice ever caused the regulatory authorities to refuse registration, to restrict the proposed therapeutic indication of a pharmaceutical, or to apply a cautionary label. It was found that no tumor findings in mice alone ever led to such a regulatory action. In addition, whether mouse studies had been important in interpreting the results of rat studies was determined. A negative mouse study (no tumors found) was rarely used to declare the rat findings irrelevant to humans. A mechanistic explanation was used as a much more important argument in the assessment of tumor findings in rats. In case of transspecies findings, the target organs were the usual ones, such as lung and liver, or the tumors occurred as a result of an exaggerated pharmacodynamic action expected from the pharmacology of the compound. The results of the database thus question the need of maintaining the requirement of rodent carcinogenicity studies in two species.

Animals↗
PubMed1996

Centred contact density functions for the statistical analysis of random sets. A stereological study on benign and malignant glandular tissue using image analysis.

Real structures investigated in the material and biological sciences, such as minerals or tissues, can often be reduced to two phases. In a stochastic approach, the components of such binary structures may be considered as the union of grains--random sets implanted with their centres at random points--and their complementary space, which is called the pore space. The simplest stochastic germ-grain model is the Boolean model of random sets, which we use here instrumentally as a null model (reference model) for comparison with our biological material. After a brief review of basic properties of the Boolean model and related statistical methods, we introduce centred contact density functions as a new approach. Empirical contact density functions are estimated from the empirical contact distribution functions with an image analyser by dilation of the grain phase. Theoretical contact density functions are then predicted from a set of image parameters, under the assumption that the Boolean model holds. A centred contact density function is the difference between the estimated and the predicted contact density function. Apart from a random error term, centred contact density functions amount to zero irrespective of the area fraction of the grain phase, when the germ-grain model is Boolean. As a section of a spatial Boolean model is a planar Boolean model, the method is also applicable in stereological studies where digitized images are obtained from sections of a three-dimensional structure. Centred contact density functions were determined for mastopathic tissue as compared to mammary cancer, and for tumour-free prostatic tissue as compared to prostatic cancer. For each category of specimens, twenty cases with 10 images each were analysed. Benign and malignant glandular tissue of the aforementioned types deviates significantly from the Boolean model. Centred contact density functions show that malignant transformation is connected with profound geometric remodelling of the pore space.

Breast Neoplasms↗
PubMed1996

Adipocere--problems in estimating the length of time since death.

Establishing the length of time since death is particularly difficult in corpses showing advanced autolysis. One sign of advanced decay is the formation of adipocere. In this state bodies show evidence of a partly wax-like and partly pasty condition. Continued storage ultimately results, among other things, in further decomposition due to the action of micro-organisms from the surrounding area-even if this is chronologically delayed. An exception is provided by the formation of adipocere under air-tight conditions. Initially, autolysis and heterolysis also occur, involving the release of fatty acids. As a result of the subsequent hydrogenation of the fats under the influence of bacterial enzymes, the unsaturated fatty acids are partially converted into saturated fatty acids. As the fatty acids clearly have a bactericidal effect, further bacterial decomposition is stopped at this early adipocere stage. Additional micro-organisms from outside can no longer penetrate when this hermetic seal is in place. In addition, the lack of calcium (e.g. from water or moist earth) can be a reason for the fact that further adipocere development, leading to wax-like hardening of the fat, is arrested. Thus the condition of the body can remain constantly preserved over many years and it no longer allows a reliable estimate to be made of the period of time since death.

Anaerobiosis↗
PubMed1995

[Old wine in new bottles: the "promille-killer" Party Plus].

We report about the allegedly new sobering up preparation called PARTY-PLUS, the ingredients of which resemble very much those of the inefficient "drink with a sobering up effect NEUKAMM-lemonade". In a drinking experiment Verum vs. Placebo (a light mineral water) the inefficiency of the alcohol elimination kinetics is proved once again, especially with regards to the extent of success suggested in advertising. Official bodies of administration of justice and legislation are called upon to oppose such doings of manufacturers and distributors more firmly. This is necessary because expected side effects and health hazards due to the high fructose contents are deliberately played down or concealed altogether.

Adult↗