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Biomedical subjects

U Schreiber

Publications and source records attributed to U Schreiber.

At least 19 recordsLinked to original sources
PubMed2007

[Primary stability of the capsule-labrum complex after reconstruction with the Mitek Bioknotless anchor system in human cadaver models].

BACKGROUND: This study examines the postoperative stability of the Mitek Bioknotless anchor system with biomechanical draw-out pulling in human cadaver shoulders. METHOD: With simulation of anterior shoulder dislocation a test group (n=10, Ø 45 years) was tested against a native group (n=8, Ø 47 years). All shoulders were dissected up to the passive stabilizers. In the test group an artificial Bankart lesion was created and repaired with three Mitek Bioknotless anchors. The humeri of both groups were fixed in 60 degrees glenohumeral abduction and 90 degrees external rotation and then dislocated in a ventral direction. For evaluation purposes the ultimate draw-out strength, mode of failure, translation of humeral head, capsular slope, and bone density in the test group were measured. RESULTS: In the test group the ultimate strength was a median of 937 N (min. 554 N, max. 1,294 N) with 28 bony anchor dislocations, 1 suture rupture, and 1 capsular rupture, and in the native group with 6 Bankart and 2 HAGL lesions it was 1,214 N (708 N, 1,471 N). The bone density showed a positive correlation to the draw-out strength regarding cortical density and total density. CONCLUSION: Regarding the high draw-out strength the Mitek Bioknotless anchor system provides enough stability for early functional treatment.

Cadaver↗
PubMed2005

The selection of a model microalgal species as biomaterial for a novel aquatic phytotoxicity assay.

A phytotoxicity assay based on the ToxY-PAM dual-channel yield analyser has been developed and successfully incorporated into field assessments for the detection of phytotoxicants in water. As a means of further exploring the scope of the assay application and of selecting a model biomaterial to complement the instrument design, nine algal species were exposed to four chemical substances deemed of priority for water quality monitoring purposes (chlorpyrifos, copper, diuron and nonylphenol ethoxylate). Inter-species differences in sensitivity to the four toxicants varied by a factor of 1.9-100. Measurements of photosystem-II quantum yield using these nine single-celled microalgae as biomaterial corroborated previous studies which have shown that the ToxY-PAM dual-channel yield analyser is a highly sensitive method for the detection of PS-II impacting herbicides. Besides Phaeodactylum tricornutum, the previously applied biomaterial, three other species consistently performed well (Nitzschia closterium, Chlorella vulgaris and Dunaliella tertiolecta) and will be used in further test optimisation experiments. In addition to sensitivity, response time was evaluated and revealed a high degree of variation between species and toxicants. While most species displayed relatively weak and slow responses to copper, C. vulgaris demonstrated an IC10 of 51 microgL-1, with maximum response measured within 25 minutes and inhibition being accompanied by a large decrease in fluorescence yield. The potential for this C. vulgaris-based bioassay to be used for the detection of copper is discussed. There was no evidence that the standard ToxY-PAM protocol, using these unicellular algae species, could be used for the detection of chlorpyrifos or nonylphenol ethoxylate at environmentally relevant levels.

Biological Assay↗
PubMed2005

The combined SPE:ToxY-PAM phytotoxicity assay; application and appraisal of a novel biomonitoring tool for the aquatic environment.

Mounting concerns regarding the environmental impact of herbicides has meant a growing requirement for accurate, timely information regarding herbicide residue contamination of, in particular, aquatic systems. Conventional methods of detection remain limited in terms of practicality due to high costs of operation and the specialised information that analysis provides. A new phytotoxicity bioassay was trialled for the detection of herbicide residues in filter-purified (Milli-Q) as well as natural waters. The performance of the system, which combines solid-phase extraction (SPE) with the ToxY-PAM dual-channel yield analyser (Heinz Walz GmbH), was tested alongside the traditional method of liquid chromatography-mass spectrometry (LC-MS). The assay methodology was found to be highly sensitive (LOD 0.1 ng L(-1) diuron) with good reproducibility. The study showed that the assay protocol is time effective and can be employed for the aquatic screening of herbicide residues in purified as well as natural waters.

Biosensing Techniques↗
PubMed2001

Epidermal transmittance of leaves of Vicia faba for UV radiation as determined by two different methods.

Leaves of Vicia faba were collected from the field and the greenhouse and transmittance of epidermal peels from adaxial and abaxial sides was determined in the wavelength range from 250 to 800 nm using a spectrophotometer equipped for the measurement of turbid samples. From the same leaves, epidermal transmittance was estimated by a recently developed fluorometric method. Both methods gave highly correlated results with a slope of the regression line between both methods close to 1 and an intercept close to 0. Transmittances at around 310 nm as low as 3% were detected in the adaxial epidermis of field-grown leaves, while transmittance could be as high as 70% in the abaxial epidermis of greenhouse-grown leaves. There was a strong correlation between UV-A (ca. 366 nm) and UV-B (ca. 310 nm) transmittance detected by both methods which could be explained by the pigment composition in methanolic extracts where flavonols accounted for 90% of the absorption at 310 nm in the extract, while hydroxycinnamic acid derivatives which absorb only at the shorter wavelength constituted about 5%. It is concluded that the fluorescence method which allows rapid measurements on intact leaves can provide a quantitative estimate of epidermal transmittance for UV-B (280-320 nm) and UV-A (320-400 nm) radiation.

Journal Article↗
PubMed2001

UV-excited chlorophyll fluorescence as a tool for the assessment of UV-protection by the epidermis of plants.

Recently, a new method for estimating epidermal transmission of UV radiation in higher plants has been proposed. The empirical evidence for the usefulness of this method is reviewed here. Direct comparison with spectroscopically determined epidermal transmission yielded equivalent results. A linear correlation to the concentration of epidermal screening compounds has been shown. Relating UV-A and UV-B absorbance allowed some preliminary conclusions about the chemical nature of the screening compounds. A new portable apparatus is presented for the first time, which allows the non-destructive assessment of UV-A screening even under field conditions. Repeated measurements on identical leaves over a time-course of 6 d demonstrated a strong age-dependence in the capacity for the synthesis of UV-A screening compounds upon exposure to UV-B radiation. It is concluded that the new method may provide a valuable tool for the investigation of the acclimation of plants to UV-B radiation and, when accompanied by HPLC analysis, of the reaction of phenolic metabolism to environmental stimuli.

Acclimatization↗
PubMed2001

Osmotic stress induces inactivation of photosynthesis in guard cell protoplasts of Vicia leaves.

Guard cell protoplasts isolated from Vicia leaves showed a strong suppression of the photosynthesis under hypotonic conditions, as reflected by changes in the chlorophyll fluorescence characteristics. The response was reversible as well. Mesophyll cell protoplasts did not show any lowering of photosynthetic activity under hypo-osmotic conditions. This result indicates that the response was guard cell specific.

Fabaceae↗
PubMed2001

Nitrogen starvation-induced chlorosis in Synechococcus PCC 7942. Low-level photosynthesis as a mechanism of long-term survival.

Cells of the non-diazotrophic cyanobacterium Synechococcus sp. strain PCC 7942 acclimate to nitrogen deprivation by differentiating into non-pigmented resting cells, which are able to survive prolonged periods of starvation. In this study, the physiological properties of the long-term nitrogen-starved cells are investigated in an attempt to elucidate the mechanisms of maintenance of viability. Preservation of energetic homeostasis is based on a low level of residual photosynthesis; activities of photosystem II and photosystem I were approximately 0.1% of activities of vegetatively growing cells. The low levels of photosystem I activity were measured by a novel colorimetric assay developed from the activity staining of ferredoxin:NADP+ oxidoreductase. Photosystem II reaction centers, as determined by chlorophyll fluorescence measurements, exhibited normal properties, although the efficiency of light harvesting was significantly reduced compared with that of control cells. Long-term chlorotic cells carried out protein synthesis at a very low, but detectable level, as revealed by in vivo [35S]methionine labeling and two-dimensional gel electrophoresis. In conjunction with the very low levels of total cellular protein contents, this implies a continuous protein turnover during chlorosis. Synthesis of components of the photosynthetic apparatus could be detected, whereas factors of the translational machinery were stringently down-regulated. Beyond the massive loss of protein during acclimation to nitrogen deprivation, two proteins that were identified as SomA and SomB accumulated due to an induced expression following nitrogen reduction.

Amino Acid Sequence↗
PubMed2000

Light-induced dynamic changes of NADPH fluorescence in Synechocystis PCC 6803 and its ndhB-defective mutant M55.

Blue-green fluorescence emission of intact cells of Synechocystis PCC6803 and of its ndhB-defective mutant M55 was measured with a standard pulse-amplitude-modulation chlorophyll fluorometer equipped with a new type of emitter-detector unit featuring pulse-modulated UV-A measuring light and a photomultiplier detector. A special illumination program of repetitive saturating light pulses with intermittent dark periods (10 s light, 40 s dark) was applied to elicit dynamic fluorescence changes under conditions of quasi-stationary illumination. The observed effects of artificial electron acceptors and inhibitors on the responses of wild-type and mutant M55 cells lead to the conclusion that changes of NAD(P)H fluorescence are measured. In control samples, a rapid phase of light-driven NADP reduction is overlapped by a somewhat slower phase of NADPH oxidation which is suppressed by iodoacetic acid and, hence, appears to reflect NADPH oxidation by the Calvin cycle. Mercury chloride transforms the light-driven positive response into a negative one, suggesting that inhibition of NADP reduction at the acceptor side of PSI leads to reduction of molecular oxygen, with the hydrogen peroxide formed (via superoxide) causing rapid oxidation of NADPH. The new fluorescence approach opens the way for new insights into the complex interactions between photosynthetic and respiratory pathways in cyanobacteria.

Cyanobacteria↗
PubMed2000

Radon and thoron in cave dwellings (Yan'an, China).

222Rn and 220Rn concentrations were measured in cave dwellings and brick houses in the region of Yan'an (China) during summer 1997. The underground dwellings are built into Quaternary loess, and all investigated houses are founded on it. The median values of indoor 222Rn and 220Rn concentrations are 42 (n = 18) and 77 Bq m(-3) (n = 15) for brick houses and 92 (n = 23) and 215 (n = 17) Bq m(-3) for cave dwellings. To classify the dwellings in respect to their "cave-character," the fraction of walls having a direct contact to the loses is calculated for each dwelling. While the 222Rn concentrations are increasing with higher fractions, the 220Rn concentrations are not correlated with this fraction. On the other hand, due to the short half-life of 220Rn the distance from the measuring point to the walls is negatively correlated with the 220Rn concentration, while there is no correlation with the 222Rn concentration. Therefore, concentric isolines of 220Rn concentrations showing a strong gradient were detected in cave dwellings. An influence of the ventilation rate is distinct for 222Rn but weak for 220Rn. The effective dose rates for 222Rn and 220Rn and their progenies are calculated for brick houses (2.7 mSv y(-1)), cave dwellings (7.1 mSv y(-1)), and for traditional cave dwellings with a bed foundation built with loess (16.7 mSv y(-1)). These calculations are based on summer measurements only. It is expected that the true effective dose rates will be significantly higher.

China↗
PubMed1998

Two distinct states of the thylakoid bf complex.

Under normal physiological conditions the state of the cyt bf complex is characterized by rapid reoxidation kinetics of cyt b-563 following flash-illumination. It is known that these kinetics are dramatically slowed down under oxidizing conditions. Here we show that this slow-down of cyt b-563 oxidation is the consequence of a relatively slow (half-time of several minutes) transformation of the cyt bf complex into a distinctly different state (termed state-s). Reversal to the normal state requires strong reductive treatment or light-induced electron transport. The results are in line with a recent model of functional cyt bf dimers [Cramer et al., Annu. Rev. Plant Physiol. Plant Mol. Biol. 47 (1996), 477-5081, if it is assumed that state-s reflects the monomeric state of the bf complex.

Chloroplasts↗
PubMed1998

In vitro investigations of drug release and penetration--enhancing effect of ultrasound on transmembrane transport of flufenamic acid.

Percutaneous absorption studies are performed in various in vitro models to determine the rate of drug absorption via the skin. We designed an phonophoretic drug delivery system to investigate the influence of ultrasound on transmembrane transport of different drugs. Phonophoresis is defined as the migration of drug molecules, contained in a contact agent, through the skin under the influence of ultrasound. We investigated the absorption of flufenamic acid in a buffer medium in dependence of ultrasound energy and application time. For evaluating membrane penetration of flufenamic acid, the concentration range of buffer solution was measured. Flufenamic acid was determined by using a fluorimetric method. Ultrasound energy was supplied for between 5 and 30 min at a range of intensities (0; 0.3; 0.6; 0.9; 1.2; 1.5 W/cm2). energy levels commonly used for therapeutic purpose. The pronounced effect of ultrasound on the transmembrane absorption of the drug was observed at all ultrasound energy level studied. The time of application was found to play an important role in delivery and transport of drug. Dependent on time, we observed an arise of temperature up to 4.5 degrees. It appears that there was no difference between an intensity of 0.3 and 1.5 W/cm2 and the measured drug concentrations in solution. The highest penetration was observed at an intensity of 1.0 W/cm2 after 30 min. These results were not significantly different from concentration in measurements after 30 min and 0.5 and 1.5 W/cm2. It seems that the arise of drug concentration is caused by effects of temperature and by variation of membrane delivery in dependence of temperature.

Biological Transport↗
PubMed1998

In vitro investigations of drug release and penetration--enhancing effect of ultrasound on transmembrane transport of flufenamic acid.

Although topical drugs are usually applied at a convenient site, the target for the drug interaction may be systemic. Phonophoresis is the use of ultrasound to enhance the delivery of topical applied drugs. The purposes of our study were to investigate the in vitro penetration and the in vivo transport of flufenamic acid in dependence of ultrasound. Percutaneous absorption studies are performed in various in vitro models to determine the rate of drug absorption via the skin. We designed a phonophoretic drug delivery system to investigate the influence of ultrasound on transmembrane transport of different drugs. We investigated the absorption of flufenamic acid in a buffer medium in dependence of ultrasound energy and application time. For evaluating membrane penetration of flufenamic acid, the concentration range of buffer solution was measured. Ultrasound energy was supplied for between 5 and 30 min at a range of intensities up to 1.5 W/cm2, energy levels commonly used for therapeutic purpose. The pronounced effect of ultrasound on the transmembrane absorption of the drug was observed at all ultrasound energy levels studied. The time of application was found to play an important role in delivery and transport of drug. Dependent on time, we observed a rise of temperature up to 4.5 degrees C. It appears that there was no difference between an intensity of 0.3 and 1.5 W/cm2 and the measured drug concentrations in solution. The highest penetration was observed at an intensity of 1.0 W/cm2 after 30 min. These results were not significantly different from concentration measurements after 30 min and 0.5 and 1.5 W/cm2. It seems that the arise of drug concentration is caused by effects of temperature and by variation of membrane delivery in dependence of temperature. Using this in vitro model we note it is possible to compare the transdermal penetration and absorption of commercial flufenamic ointment in volunteers.

Administration, Topical↗
PubMed1997

[Pain intensity and power densities of therapeutic ultrasound--a serial, comparative pilot study in patients with low back pain].

INTRODUCTION: A pilot study was conducted to provide an indication of the power density (PD) dependent analgesic effect of ultrasound (US) under serial application in patients with low back pain. METHODS: Thirty patients (n=3 x 10) were randomly assigned to one of three PDs (0.3, 0.7 or 1.0 W/cm(2)). Twelve treatments were applied once a day for 2 weeks. The sonation time per treatment was 10 minutes. Patients were unaware of their grouping. Pain intensity (PI) was assessed using a visual analogue scale for each treatment. The relationship between the different PI profiles was tested by repeated measures by ANOVA. RESULTS: The averaged duration of pain was over 10 years (chronic low back pain). Twenty-seven (n=3 x 9) patients could be analyzed (three drop-outs). In the medium (0.7 W/cm(2)) and high (1.0 W/cm(2)) PD groups the PI showed a clearly decreasing trend, while in the low (0.3 W/cm(2)) PD group, the PI remained stationary. None of the contrasts showed a locally significant effect (Bonferroni adjustment). CONCLUSIONS: The observed effect is presumably overestimated. In the low PD group, there were more people out of work, and fewer took analgesic drugs. No conclusive judgement is possible. The concept of the PD-dependent effect of US must be evaluated in trials with greater sample sizes.

Clinical Trial↗
PubMed1997

Kinematic and neuromuscular changes of the gait pattern after Achilles tendon rupture.

After long immobilization periods in equinovalgus with operated Achilles tendon rupture, long-lasting changes of motor patterns in functional movement can be expected. In the present study, possible alterations in gait pattern have been analyzed based on kinematic and neuromuscular parameters. Ten patients 1 year after surgery and a healthy control group performed 10 gait cycles in natural walking cadence. Ankle motion, pressure distribution, and electromyographic data were recorded and analyzed in defined phases. Kinematic and neuromuscular changes are still evident 1 year after surgery with a temporal phase shift and a neuromuscular deficit of the lateral gastrocnemius muscle. The objective of rehabilitation should be the facilitation of the temporal innervation pattern of the lateral gastrocnemius muscle in the functional movement.

Achilles Tendon↗