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Biomedical subjects

W Hofmann

Publications and source records attributed to W Hofmann.

At least 37 records · Page 2Linked to original sources
PubMed2005

[GPS--good practice secondary data analysis. Working Group for the Survey and Utilization of Secondary Data (AGENS) of the German Society for Social Medicine and Prevention (DGSMP)].

The scientific use of secondary data, especially of claims data from health insurance funds, has continuously increased in the last years. Therefore the Working Group "Collection and Use of Secondary Data" (AGENS) of the German Society of Social Medicine and Prevention (DGSMP) took the initiative to define quality standards for secondary data analysis. Starting with a review of the Good Epidemiologic Practice (GEP) AGENS adapted the GEP to the specific requirements of secondary data analysis by a multi-stage consensus process. The guideline Good Practice Secondary Date Analysis (GPS) was adopted on January 15 (th), 2005. GPS consists of 10 guidelines which are divided in explaining comments and recommendations. The GPS are targeted to set up standards for secondary data analysis, and they may also be used as a foundation of contracts between data owners and scientists. They are addressed to scientists from health services research and social medicine. AGENS commits itself to revise GPS continuously.

Benchmarking↗
PubMed2004

Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions.

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).

Journal Article↗
PubMed2004

High-energy particle acceleration in the shell of a supernova remnant.

A significant fraction of the energy density of the interstellar medium is in the form of high-energy charged particles (cosmic rays). The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically, unequivocal evidence for the production of high-energy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.7 - 3946 (G347.3 - 0.5), which was discovered by ROSAT in the X-ray spectrum and later claimed as a source of high-energy gamma-rays of TeV energies (1 TeV = 10(12) eV). We present a TeV gamma-ray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very-high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks.

Journal Article↗
PubMed2004

Limb-salvage by femoro-distal bypass and free muscle flap transfer.

OBJECTIVES: To evaluate the feasibility and long-term outcome of distal arterial reconstruction combined with free muscle flap transfer for patients who would otherwise have undergone major amputation. METHODS: Between 1996 and 2001, 27 reconstructions using autologous vein were performed in 25 patients. Seventeen of these patients had diabetes mellitus. Gracilis, rectus abdominis and latissimus dorsi muscles were used as free flaps, covered with split-thickness skin grafts. RESULTS: Eighty-five percent of patients had a patent graft and viable muscle flap after 1-month. Mean follow-up was 51 months (4-72 months). At the time of follow-up 77% of reconstructions were patent and 70% of patients regained full functional capacity of their lower extremities. CONCLUSION: Limb-salvage by distal arterial reconstruction and free muscle flap transfer, is feasible with low mortality and morbidity and provides excellent long-term results with regard to graft patency and functional status.

Arteriovenous Shunt, Surgical↗
PubMed2004

Stochastic simulation of alveolar particle deposition in lungs affected by different types of emphysema.

In the present study, disease-specific stochastic models were developed for the computation of particle deposition in lungs affected by COPD, emphysema, or both, distinguishing between four types of pulmonary emphysema-centriacinar, paraseptal, panacinar, and bullous. To simulate COPD, airway calibers of the tracheobronchial tree were randomly reduced between 20% and 50% in each airway. For the study of pure COPD ("blue bloaters"), alveolated airway dimensions of the healthy lung were used, while for the simulation of emphysema without COPD ("pink puffers"), normal conductive airway diameters were assumed. Deposition calculations in diseased lungs were carried out by assuming (a) identical inspiration and expiration times (no breath-hold time) and (b) a continuous increase of the functional residual capacity (from 3,300 to 5,000 mL), accompanied by a simultaneous drop of the tidal volume (from 1,000 to 500 mL). Independent of particle size, total alveolar deposition in emphysematous lungs was significantly decreased relative to normal lungs. In particular, the deposition maximum at large particle sizes, which is a characteristic for healthy subjects, completely disappeared. Among the various emphysema models, deposition was smallest in lungs with bullous emphysema due to strongly enhanced settling and diffusion distances within the alveolar structures. A change of the lung volume caused a further decrease in particle deposition. Alveolar deposition in "blue bloaters" and "pink puffers" was very similar to the deposition in patients suffering from COPD and emphysema. Alveolar deposition per acinar airway generation was also strongly reduced in diseased lungs compared to normal lungs. Besides this reduction, deposition patterns became more uniform throughout the alveolar region.

Aerosols↗
PubMed2004

Interaction of alpha particles at the cellular level--implications for the radiation weighting factor.

Since low dose effects of alpha particles are produced by cellular hits in a relatively small fraction of exposed cells, the present study focuses on alpha particle interactions in bronchial epithelial cells following exposure to inhaled radon progeny. A computer code was developed for the calculation of microdosimetric spectra, dose and hit probabilities for alpha particles emitted from uniform and non-uniform source distributions in cylindrical and Y-shaped bronchial airway geometries. Activity accumulations at the dividing spur of bronchial airway bifurcations produce hot spots of cellular hits, indicating that a small fraction of cells located at such sites may receive substantially higher doses. While presently available data on in vitro transformation frequencies suggest that the relative biological effectiveness for alpha particles ranges from about 3 to 10, the effect of inhomogeneous activity distributions of radon progeny may slightly increase the radiation weighting factor relative to a uniform distribution. Thus a radiation weighting factor of about 10 may be more realistic than the current value of 20, at least for lung cancer risk following inhalation of short-lived radon progeny.

Air Pollutants, Radioactive↗
PubMed2004

Survival of dairy cows after surgery to correct abomasal displacement: 1. Clinical and laboratory parameters and overall survival.

The objective of this study was to compare the clinical and laboratory consequences of left and right displacement of the abomasum (LDA and RDA), short- and long-term survival after surgery and the findings in cows, that could not be cured by omentopexy. Data from 564 cases of displaced abomasum (466 LDA, 98 RDA) were analysed retrospectively. Clinical and laboratory findings were compared between the two manifestations of DA. Survival was assessed after 10 days and after 15 months. Necropsy was carried out on cows that died or were killed. On arrival at the clinic, left displacement of the abomasum (LDA) cows had been recognized as diseased for longer. LDA occurred earlier in lactation, and more cows with right displacement of the abomasum (RDA) were pregnant. Overall clinical symptoms were more severe in RDA than in LDA cows. Heart rate was higher, body temperature was lower, inanition, abnormal faeces and ruminal stasis were more frequent in RDA cows. Leucocyte counts were higher, and potassium and chloride levels were lower in RDA cows. Acetonuria was more frequent in LDA cows. More LDA than RDA cows were released from the clinic as cured (82.0% versus 74.5%). However, survival after the early post-surgical period was similar for RDA and LDA cows. At necropsy, diseases of the gastrointestinal system were the predominant finding in RDA cows, while in LDA cows, diseases of the liver and other concurrent diseases were more important.

Abomasum↗
PubMed2004

Survival of dairy cows after surgery to correct abomasal displacement: 2. Association of clinical and laboratory parameters with survival in cows with left abomasal displacement.

This study examines the association of pre-surgical clinical parameters in cows with left displacement of the abomasum (LDA) with the probability of cure. Data from 466 cases of LDA in which omentopexy was performed were analysed. Cows were classified in three categories according to the outcome of treatment. Cows in the first category were cured, i.e. sent back to the farm for further milk production. Cows in the second category were sent for slaughter because of an unfavourable prognosis concerning productivity. Cows in the third category either died or were salvaged because of poor prognosis concerning survival. Factors were examined for their possible influence on the outcome of treatment by comparing the values of successfully treated cows to those cows that either died or had to be sent for slaughter. Factors that were associated with a favourable prognosis were a short duration of disease, an undisturbed general condition, good appetite, normal faeces, a higher body weight, lower haematocrit, haemoglobin and erythrocyte counts, lower urea, AST and bilirubin, and higher sodium, potassium and chloride concentrations compared with cows with an unfavourable prognosis. Haemoconcentration was associated with higher AST, bilirubin and urea and with low sodium, potassium and chloride. Acetonuria was associated with increased AST and bilirubin and low urea. Low sodium and potassium concentrations were associated with an impaired general condition. It is concluded that a thorough clinical examination with special emphasis on general condition, liver function and dehydration status is of great importance in determining the prognosis of abdominal surgery in cows with LDA.

Abomasum↗
PubMed2003

[Tolerance and effectiveness of oxymetazoline and xylometazoline in treatment of acute rhinitis].

BACKGROUND: Local alpha-sympathomimetics in hydrous solution are well known in the therapy of acute rhinitis and sinusitis. However, added preservatives like benzalkonium chloride have a negative effect on compatibility. PATIENTS AND METHOD: A total of 307 patients with acute rhinitis entered the study. The treatment with oxymetazoline with preservative, oxymetazoline without preservative and xylometazoline with preservative was evaluated. RESULTS: This randomised, double-blind, multi-centered, verum-controlled tolerance study confirmed that the local sympathomimetics oxymetazoline and xylometazoline are well tolerated in the treatment of acute rhinitis. When evaluated according to the parameters "feeling of dryness in nasal mucosa" and "burning sensation", the Nasivin sanft 0.05% spray, which contains the active agent oxymetazoline without preservatives, proved to be considerably superior to preparations containing the preservative benzalkonium chloride. CONCLUSION: Preparations without preservatives should be the preferred choice of treatment for acute rhinitis.

Acute Disease↗
PubMed2003

[High utilization of health care services by older adults].

Present discussions on health-care policy focus on fundamental restructuring, which will supposedly enable a more efficient provision of health care to patients with chronic ailments and also to elderly persons. Apart from increasing health care expenditure, the need for reform arises from demographically determined aging of the German population. A total of 54% of the 'GKV's' turnover in medical drugs is attributed to the health insurance agency's enrollees, who are aged 60 years and older, although they make up just 25% of total membership. Elderly men and women are therefore a significant group of health care users. In spite of its enormous political relevance, the provision of health care for the elderly has seen only marginal examination in Germany. This study on the "high utilization of health care services by older men and women" focuses on the examination of health care utilization by people aged 60 years and over. The following article will first introduce the study design. It will then review the literature on aging and health and on health care utilization by the elderly. The article goes on to present interim findings on the characteristics of the examined cohort and on ist consumption of medical drugs. The analysis is based on data regularly recorded by a North German health insurance agency. The examined cohort consists of 54% men and 46% women, whereby the average age is 68.3 years. The data analysis shows that 73,454 of the enrollees aged 60 years and older consumed 1,395,515 prescribed drugs in 2000. Each enrollee received an average of 19 medications annually; 5% of all those men and women examined received more than 58 medicines and were thus responsible for approximately a fifth of the volume in prescriptions. Of the drugs prescribed, 28.4% were for the treatment of cardio-vascular diseases, 13.9% for alimentary and metabolic disorders and 13.1% for the treatment of neurological diseases. Men and women aged 60 years and over are responsible for expenditure on medical drugs of 81,856,139 Deutsche Mark (41,926,298 Euro). On the average each enrollee generates costs of 1,114,00 Deutsche Mark (570 Euro), whereby every second one is responsible for an amount of less than 570 Deutsche Mark (291 Euro). A mere 5% of all enrollees is responsible for one third (32.1%) of the total drug expenditure. In closing the article will outline this research project's further course of action.

Age Factors↗
PubMed2003

Mechanistic interpretation of the slow bronchial clearance phase.

A slow bronchial clearance phase, describing the removal of insoluble particles from the sol layer, has recently been incorporated into the ICRP human respiratory tract model. A striking feature of that clearance phase is the size dependence of the slowly cleared fraction. In the theoretical approach presented here, it is suggested that the slow bronchial clearance phase includes three main mechanisms: (1) re-transfer of particles onto the gel layer after a certain time delay, (2) intra- or intercellular transfer of particles through the airway epithelium and subsequent transport to the blood or lymph nodes, and (3) uptake of particles by airway macrophages. The experimentally observed inverse relationship between the slow clearance fraction and geometric particle size is interpreted as an increasing capture probability in the sol layer and transepithelial transport with decreasing particle diameter.

Absorption↗
PubMed2003

Simulation of deposition and clearance of inhaled particles in central human airways.

In this study local distributions of deposited inhaled particles such as radon progenies in realistic human airway bifurcation models of bronchial generations one to six are computed for different geometries, inlet flow profiles, flow rates and particle sizes with computational fluid particle dynamics methods. The movement of the mucus layer in the large central human airways is also simulated by computational fluid dynamic techniques. There is experimental evidence that bronchogenic carcinomas mainly originate at the central zone of the large airway bifurcations, where primary hot-spots of deposition have been found. However, current lung deposition models do not take into consideration the inhomogeneity of deposition within the airways. The inhomogeneous movement of the mucus layer may strongly influence the effect of primary deposition. On the basis of our results, both the deposition and the clearance patterns are highly non-uniform, especially in the vicinity of the carinal ridge of the bifurcations.

Absorption↗
PubMed2003

Stochastic model of ultrafine particle deposition and clearance in the human respiratory tract.

Deposition and clearance of insoluble ultrafine particles, ranging from 1 to 100 nm, were simulated by stochastic models using Monte Carlo methods. Brownian motion is the dominant mode of deposition in human airways. The additional effects of convective diffusion in bifurcations and axial diffusion (convective mixing) primarily affect particle transport and deposition of particles in the 1-10 nm range. Regarding total deposition, the effects of both convective mechanisms are practically compensated by the concomitant effect of molecular radial diffusion (Brownian motion). During the first hours following inhalation, 1 nm particles are predicted to be cleared much faster than particles in the size range from 10 to 100 nm, with a retained fraction of about 80% after 24 h. For 1-10 nm particles, extracellular transfer to blood is the most likely mode of clearance, while uptake and subsequent accumulation in epithelial cells are assumed to be the preferential mechanisms for 10-100 nm particles.

Adsorption↗
PubMed2002

Testing extrapolation of a biologically based exposure-response model from in vitro to in vivo conditions.

Models of carcinogenesis may become so flexible as to preclude the possibility of being falsified by data. This problem is removed in part by stronger biophysical specification of processes and parameters within the model prior to fitting to in vivo data on the relationship between exposure and cancer incidence. This paper explores the use of a biophysical model of chromosomal damage, cellular transformation, repair, mitosis, initiation, promotion, progression, and cytotoxicity in developing exposure-response models for radiation-induced cancer. Many of the aspects of model form and parameter values are developed from in vitro data, and the model then is extrapolated to the in vivo setting using a dosimetric model to account for dose inhomogeneity within the lung tissue of rats exposed to radon progeny in air. The ability of the model to predict cancer incidence in the rats is assessed and is shown to be problematic at higher doses. This calls into question whether a full claim may be made about the ability of first-principle models to fully constrain models applied to in vivo data at present. Possible explanations for the discrepancy, and implications for extrapolation, are provided.

Animals↗
PubMed2002

Explanation of protective effects of low doses of gamma-radiation with a mechanistic radiobiological model.

PURPOSE: To test whether data that show protective effects of low doses against spontaneous neoplastic transformation of C3H 10T1/2 cells can be explained with a biomathematical model that includes radioprotective mechanisms. To link important features of the model to known biological processes. MATERIALS AND METHODS: The model simulates double-strand break formation in transcriptionally active and in bulk DNA, translocation of DNA segments, and the fixation of damage at mitosis; promotion is also included. The model equations were solved numerically using a stiff solver. RESULTS: The data were successfully simulated by the model: cell transformation-reducing effects of low doses of gamma-radiation delivered at low dose-rates are explained by radiation-inducible DNA repair and enzymatic scavenging. CONCLUSIONS: The model successfully simulates experimental data. The highly nonlinear features of the data point to a nonlinear dose-effect relationship at low doses and indicate that linear extrapolation from moderate (or high) to low doses and dose-rates may not be justified for in vitro studies of the cell line under consideration.

Animals↗
PubMed2002

Modelling carcinogenic effects of low doses of inhaled radon progenies.

In this study, cellular hit probabilities of alpha particles emitted by inhaled radon progenies in sensitive epithelial cell nuclei were simulated at low exposure levels to obtain useful data for the rejection or in support of the linear no-threshold dose-effect hypothesis. In this work, local distributions of deposited inhaled radon progenies in airway bifurcation models were computed at exposure conditions which are characteristic of homes and uranium mines. Then, maximum local deposition enhancement factors, that is, local per average deposition densities, were simulated, and the effects of the inhomogeneity of deposition on hit probabilities were characterised. Our results suggest that in the vicinity of the carinal regions of the central airways the probability of multiple hits can be quite high even at low doses.

Administration, Inhalation↗
PubMed2002

Energy deposition, cellular radiation effects and lung cancer risk by radon progeny alpha particles.

Slowing down spectra, LET spectra, hit probabilities, and radiation doses were simulated for the interaction of single 218Po and 214Po alpha particles with sensitive basal and secretory cell nuclei in the bronchial epithelium of human and rat lungs for defined exposure conditions. Probabilities per unit track length for transformation, derived from in vitro experiments with C3H 10T1/2 cells, were used to estimate transformation probabilities for randon progeny alpha particles in basal and secretory cells. Different weighting schemes were assumed to relate cellular hit probabilities, doses and transformation probabilities, obtained for different cell depths and airway generations, to lung cancer risk per unit exposure. In vitro transformation and in vivo lung cancer incidence were simulated by a state-vector model which provides a stochastic formulation of dose-rate dependent cellular transitions related to formation of double strand breaks, repair, inactivation, stimulated mitosis and promotion through loss of intercellular communication.

Alpha Particles↗