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Biomedical subjects

F Schweitzer

Publications and source records attributed to F Schweitzer.

At least 19 recordsLinked to original sources
PubMed2005

[Fundus spectrometry in age-related maculopathy].

BACKGROUND: Spectroscopic methods permit the non-invasive detection of fundus pigments by the wavelength-dependent absorption of fluorescence as well as by the fluorescence lifetime. From the relative concentrations of haemoglobin and oxyhaemoglobin, the oxygen saturation can be calculated. The onset of age-related maculopathy might be delayed by a high optical density of xanthophyll. The detection of alterations in fundus autofluorescence points to age-related pathomechanisms (accumulation of lipofuscin, formation of connective tissue). The detection of autofluorescence of redox-pairs of coenzymes results in information about metabolic states at the cellular level, and might make possible an early detection of age-related changes when they are still reversible. METHOD: The evaluation of reflectance spectra, detected by imaging ophthalmo-spectrometry, results in the calculation of oxygen saturation or in the optical density of xanthophyll or of melanin. Fluorescence spectra can be measured also by this technique. For the 2-dimensional determination of the distribution of xanthophyll, a very simple method was developed, requiring fundus illumination by one wavelength only. In the detection of time-resolved autofluorescence, the fluorescence lifetime is used for the determination of endogenous fluorophores. RESULTS: As result of comparing studies between ARM patients and healthy subjects, the consumption of retinal oxygen was increased already in the children of ARM patients. An increasing optical density of xanthophyll was determined after lutein supplementation. Differences in fluorescence lifetime were determined between ARM patients and healthy subjects, but their interpretation requires investigations of cell or of organ model cultures. CONCLUSIONS: The described methods permit in vivo basic investigations of ARM and can be considered as impulses for the development of diagnostic devices.

Adult↗
PubMed2005

[Limits of the confocal laser-scanning technique in measurements of time-resolved autofluorescence of the ocular fundus].

GOAL: The 2-dimensional measurement of the time-dependent autofluorescence has in combination of confocal laser scanner technique and time correlated single photon counting the potential for the investigation of the metabolism state at the eye ground. It was to be examined, to what extent these measurements are influenced through the auto-fluorescence of the crystalline lens. MATERIAL AND METHOD: The time-dependent auto-fluorescence was measured on eyes of 21 patients with age-related macular degeneration (AMD) and of 26 healthy subjects in 40 degrees fundus images. The experimental set-up used, was developed at the eye clinic of the University of Jena. In this scanning laser ophthalmoscope, the fundus was excited at 446 nm by pulses of 100 ps full width at half maximum and 40 MHz repetition rate. The auto-fluorescence was detected with a time resolution of 25 ps for wavelengths > 500 nm. The dynamic auto-fluorescence of each pixel was approximated by a tri-exponential model function. In order to determine the influence of the fluorescence of the crystalline lens, healthy eyes and eyes were compared with implanted artificial intra-ocular lenses. For comparison the frequency distributions were used, which the decay times t1, t2 and t3 in the fundus images had been calculated with. RESULTS: Clear differences were shown in the frequency distributions of the fluorescence lifetimes between AMD-patients and healthy subjects, It resulted, however, from a crucial analysis that the fluorescence of the crystalline lens is not suppressed by the confocal laser scanning principle sufficiently. In particular the long lifetime t3 is overlapped by the fluorescence of the crystalline lens of about 4.6 ns. To the complete suppression of the influence of the lens fluorescence in measurements of the time-resolved fundus auto-fluorescence it is suggested to combine the confocal laser scanning technique with the principle of the aperture diaphragm division. CONCLUSION: In order to be able to determine the capability of measurements of the time-dependent fundus auto-fluorescence as diagnostic tool exactly, the influence of the crystalline lens is to reduce through the combination of confocal laser scanning ophthalmoscopy with the principle of the aperture diaphragm division diversely.

Fluorescein Angiography↗
PubMed2004

[Spectral separation in ocular fundus autofluorescence images in patients suffering from age-related macular degeneration].

INTRODUCTION: Alterations in the intrinsic ocular fundus fluorescence are under discussion particularly in connection with age-related macular degeneration. However, further knowledge of the chemical substrate of fluorescence is necessary. METHOD: Ocular fundus autofluorescence was observed using a fundus camera. The fluorescence emission was recorded using a 3-chip CCD camera. For comparison, the fluorescence spectra of lipofuscin, A2-E, FAD, NADH(2) and AGE's were recorded by the Jena ophthalmo-spectrometer. RESULTS: In contrast to the homogeneous intrinsic fluorescence of a normal fundus, the fluorescence images of patients suffering from AMD showed remarkable local differences. The detected fluorescence spectra showed remarkable overlaps. DISCUSSION: We introduced a new technique enabling the detection of spectral differences in images of ocular fundus autofluorescence. Besides the fluorescence of lipofuscin, we found a green one in patients suffering from nonexudative AMD.

Adult↗
PubMed2001

Statistical mechanics of canonical-dissipative systems and applications to swarm dynamics.

We develop the theory of canonical-dissipative systems, based on the assumption that both the conservative and the dissipative elements of the dynamics are determined by invariants of motion. In this case, known solutions for conservative systems can be used for an extension of the dynamics, which also includes elements such as the takeup/dissipation of energy. This way, a rather complex dynamics can be mapped to an analytically tractable model, while still covering important features of nonequilibrium systems. In our paper, this approach is used to derive a rather general swarm model that considers (a) the energetic conditions of swarming, i.e., for active motion, and (b) interactions between the particles based on global couplings. We derive analytical expressions for the nonequilibrium velocity distribution and the mean squared displacement of the swarm. Further, we investigate the influence of different global couplings on the overall behavior of the swarm by means of particle-based computer simulations and compare them with the analytical estimations.

Journal Article↗
PubMed2001

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in renal failure patients.

BACKGROUND: Nitric oxide (NO) synthesis is inhibited by the ADMA that accumulates in the plasma of patients with renal failure; however, the concentration of SDMA also is enhanced. Therefore, it has been hypothesized that ADMA and SDMA may contribute to hypertension in these patients. METHODS: We measured the concentrations of ADMA, SDMA and 21 endogenous amino acids in 257 persons by high pressure liquid chromatography (HPLC). RESULTS: The plasma concentrations of both ADMA and SDMA were significantly elevated in patients with chronic renal failure (CRF). The increase was more pronounced for SDMA (2.05 +/- 0.1 micromol/L vs. 0.5 +/- 0.04 micromol/L), whereas it was only moderate for ADMA (0.85 +/- 0.03 micromol/L vs. 0.73 +/- 0.06 micromol/L). In dialysis patients, the concentrations were further increased (ADMA, 1.05 +/- 0.04 micromol/L; SDMA, 2.68 +/- 0.13 micromol/L). After kidney transplantation, the concentration of SDMA returned to the baseline value (1.15 +/- 0.11 micromol/L), but that of ADMA remained enhanced (0.99 +/- 0.06 micromol/L). CONCLUSIONS: In CRF, especially the concentration of SDMA is significantly increased. Not only ADMA, but also SDMA are likely to be responsible for hypertension. Competition for reabsorption between SDMA and arginine within the kidney has to be considered for the interpretation of changes in the ratio between dimethylarginines and arginine in renal failure. Hemodialysis is not suitable for a long-lasting removal of methylarginines. Whether the administration of arginine could have promising effects on hypertension and complications of CRF needs to be studied in prospective trials.

Adult↗
PubMed2001

Racial and ethnic disparities in infant mortality: risk in social context.

This article presents the multifaceted efforts of Syracuse Healthy Start, a federally funded initiative of the Onondaga County Health Department and over 20 partnering agencies to reduce racial and ethnic disparities in infant mortality. The analyses presented in this article demonstrate that many women--Caucasian, African American, and Hispanic--have serious risks for low birth weight and infant death. In many cases, multiple, simultaneous risks complicate a pregnant woman's situation and in other cases the longitudinal cumulative risks impact health across generations. Infant mortality decreased overall, and for both Caucasian and African American infants during the first 3 years of the project.

Black or African American↗
PubMed1999

Active Brownian particles with energy depots modeling animal mobility.

In the model of active motion studied here, Brownian particles have the ability to take up energy from the environment to store it in an internal depot and to convert internal energy into kinetic energy. Considering also internal dissipation, we derive a simplified model of active biological motion. For the take-up of energy two different examples are discussed: (i) a spatially homogeneous supply of energy, and (ii) the supply of energy at spatially localized sources (food centers). The motion of the particles is described by a Langevin equation which includes an acceleration term resulting from the conversion of energy. Dependent on the energy sources, we found different forms of periodic motion (limit cycles), i.e. periodic motion between 'nest' and 'food'. An analytic approximation allows the description of the stationary motion and the calculation of critical parameters for the take-up of energy. Finally, we derive an analytic expression for the efficiency ratio of energy conversion, which considers the take-up of energy, compared to (internal and external) dissipation.

Animals↗
PubMed1998

Estimation of megacity growth: simple rules versus complex phenomena.

"The growth of large urban aggregates (megacities) is analogous to the development of self-organized structures known in physics. Using empirical data about changes in the built-up areas of different cities as input, the self-organizing model employed here suggests that megacities evolve towards a hierarchical form of spatial organization, and provides estimates of the size of subclusters that compose the urban aggregate.... The model has been validated by reproducing the evolution of the Berlin area over a period of 35 years (1910-45). Using the same assumptions, the evolution of the built-up area of Daegu (Korea) is simulated up to the year 2010."

Asia↗
PubMed1997

Active random walkers simulate trunk trail formation by ants.

A simple model for interactive structure formation is studied to simulate the trail formation by ants based on local chemical communication. In our model, active random walkers, which do not have the ability of visual navigation or storage of information, first have to discover different distributions of food sources and then have to link these sources to a central place by forming a trail, using no other guidance than the chemical markings produced by themselves. The simulations show the spontaneous emergence of a collective trail system due to self-organization, which is both stable and flexible, to include newly discovered sources. The typical dendritic foraging patterns of desert ants, reported by Hölldobler and Möglich (Insectes Sociaux. 1980. 27(3). pp. 237 264) are reproduced by the simulations.

Animals↗
PubMed1997

Optimization of road networks using evolutionary strategies

A road network usually has to fulfill two requirements: (i) it should as far as possible provide direct connections between nodes to avoid large detours; and (ii) the costs for road construction and maintenance, which are assumed proportional to the total length of the roads, should be low. The optimal solution is a compromise between these contradictory demands, which in our model can be weighted by a parameter. The road optimization problem belongs to the class of frustrated optimization problems. In this paper, a special class of evolutionary strategies, such as the Boltzmann and Darwin and mixed strategies, are applied to find differently optimized solutions (graphs of varying density) for the road network, depending on the degree of frustration. We show that the optimization process occurs on two different time scales. In the asymptotic limit, a fixed relation between the mean connection distance (detour) and the total length (costs) of the network exists that defines a range of possible compromises. Furthermore, we investigate the density of states, which describes the number of solutions with a certain fitness value in the stationary regime. We find that the network problem belongs to a class of optimization problems in which more effort in optimization certainly yields better solutions. An analytical approximation for the relation between effort and improvement is derived.

Journal Article↗
PubMed1989

[Surgical treatment of spinal deformity due to cerebral motor disorders using a Luque type appliance].

The authors report a series of 20 cerebral palsy patients with spine deformities who need a surgical treatment. The procedure is a posterior approach and a segmental spine instrumentation: Luque-Galvestone or Cotrel-Dubousset-Luque type. Vertebral bone-graft is always performed and sacral bone is fused 16 times. Sitting position is authorized 4 to 7 days after the operation. Improvement of frontal and sagital curves as well as pelvic obliquity is of 50% and remains unchanged with a two years follow-up. Among the complications, most of them are pulmonary infections with 2 severe cases on 9 patients. Even functional status is also improved, post-operative pains and social difficulties are frequent during almost 6 months.

Activities of Daily Living↗
PubMed1989

[The acrodynic form of the Riley-Day syndrome].

The authors report the case of a 10-year-old girl who died after suffering from severe erythromelalgia combined with digestive and general disorders associated with multiple vegetative disturbances (high blood pressure, hypothermia, colic and urinary disorders, raised catecholamine levels) for 2 years. Although the appearance of the tongue was normal and in spite of the absence of genetic criteria the diagnosis of Riley-Day dysautonomia was made and its association with neural crest disorders was indicated.

Child↗
PubMed1988

Coffin-Lowry syndrome: a multicenter study.

The Coffin-Lowry syndrome is an inherited syndrome of mental retardation, characteristic facies and skeletal anomalies. The occurrence of severe manifestations in males, with no instance of male-to-male transmission, suggests an X-linked inheritance. The paper describes seven families from five European Centers.

Adult↗
PubMed1980

[Children's mandible fractures (author's transl)].

At Lyon's Maxillo-facial Surgery Center, children's mandible fractures represent 8% treated fractures at admited sick people (35 children for 56 fractures) for 1976-77-78. We insist on the treatment used in our center for articular region fractures: mandibular gymnastic in propulsion and laterality with a good result, orthopedic treatment only in case of gymnastic's failure. The other anatomic types are treated by orthopedic, surgical or mixed method, according to teething age, and fracture's diastasis.

Adolescent↗