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Biomedical subjects

H Weber

Publications and source records attributed to H Weber.

At least 145 records · Page 8Linked to original sources
PubMed1996

Metal-on-metal articulation for artificial hip joints: laboratory study and clinical results.

As wear is inevitable with artificial joint replacement, it has to be minimized to avoid possible aseptic loosening following osteolysis due to particle-initiated foreign body reaction. Co-Cr-Mo-C alloys have a long history with only minimum wear when articulating with themselves. This investigation shows that the choice of the alloy has an effect on the wear rate of this articulation couple. Tribological studies in a screening device, a pendulum apparatus and a hip joint simulator showed a marked influence of the environment as well as the diameter of the implants with metal-on-metal articulation. A wear-resistant combination with low friction characteristics has been developed by using a wrought Co-Cr-Mo-C alloy and reducing the implant diameter to 28 mm. Clinical wear rates are comparable with laboratory data and demonstrate the potential of the metal-on-metal articulation to solve the problem of wear-induced osteolysis of hip joint endoprostheses.

Bone Cements↗
PubMed1996

Regulation and function of the tissue-specific transcription factor HNF1 alpha (LFB1) during Xenopus development.

We review the data available on the structure, developmental appearance and embryonic regulation of the tissue-specific transcription factor HNF1 alpha (LFB1) in Xenopus. The expression of the HNF1 alpha gene starts early in embryogenesis shortly after mid-blastula transition and the protein accumulates in the region of the embryo where liver, pronephros and gut--tissues that contain HNF1 alpha in the adult--are developing. The cofactor DCoH, known to stabilize dimer formation of HNF1 alpha, is present as a maternal factor in the egg and has a partially distinct tissue distribution compared to HNF1 alpha. This implies that DCoH does not only modulate HNF1 alpha dimerization but may also cooperate with other transcription factors. By injecting HNF1 alpha promoter CAT constructs into fertilized Xenopus eggs we obtained activation of the injected gene restricted to the region of the developing larvae expressing endogenous HNF1 alpha. Deletion analysis allowed to define the OZ-element that is essential for embryonic activation. This element also occurs in other promoters activated at mid-blastula transition in the embryo and interacts with the maternal factor OZ-1. As the HNF1 alpha promoter also contains functional binding sites for HNF4 and HNF1, we postulate that all of these transcription factors contribute to the cascade leading to proper embryonic activation of the HNF1 alpha gene.

Animals↗
PubMed1995

Oxidative release of nitric oxide accounts for guanylyl cyclase stimulating, vasodilator and anti-platelet activity of Piloty's acid: a comparison with Angeli's salt.

The decomposition of benzenesulphohydroxamic acid (Piloty's acid; PA) and some of its derivatives has been reported to yield nitroxyl ions (NO-), a species with potent vasodilator properties. In a previous study we demonstrated that the oxidative breakdown of PA results in the formation of nitric oxide (NO) and suggested that NO rather than NO- may account for its vasorelaxant properties. Using isolated aortic rings in organ baths, we now show that high concentrations of cysteine potentiate the vasorelaxant response to PA, whereas responses to Angeli's salt (AS), a known generator of NO-, were almost completely inhibited. These different behaviours of PA and AS are mirrored by their distinct chemistries. By using HPLC it was shown that, at physiological pH and in the absence of oxidizing conditions, PA is a relatively stable compound. Direct chemical determination of NO, stimulation of soluble guanylyl cyclase, and measurement of platelet aggregation under various experimental conditions confirmed the requirement for oxidation to release NO from PA, and quite weak oxidants were found to be sufficient to promote this reaction. In contrast, at pH 7.4 AS decomposed rapidly to yield nitrite (NO2-) and NO-, bu did not produce NO on reaction with dioxygen (O2) or hydrogen peroxide (H2O2). Thus sulphohydroxamic acids are a new class of thiol-independent NO-donors that generate NO rather than NO- under physiological conditions.

Animals↗
PubMed1995

Lumbar spinal stenosis. Clinical and radiologic features.

STUDY DESIGN: A prospective, randomized study of patients with symptomatic lumbar spinal stenosis. OBJECTIVES: Evaluation of clinical and radiologic characteristics and relationship. SUMMARY OF BACKGROUND DATA: The diagnosis of lumbar spinal stenosis is frequently used and represents a wide variety of patients with more or less well-defined spinal disorders. METHODS: One hundred patients who met inclusion criteria were consecutively selected from a neurology department and examined clinically and radiologically with plain radiography, myelography, and computed tomographic imaging. RESULTS: Duration of complaints was long, and multilevel, bilateral afflictions were common. The dominanting symptoms were sciatica, neurogenic claudication, and low back pain. The clinical findings were modest. Narrowness in the spinal canal was demonstrated radiologically with signs of compression on nerve roots, centrally and/or laterally. The radiologic findings were more extensive than expected from the clinical symptoms and signs. In most patients the sagittal diameter of the spinal canal increased on flexion and decreased on extension of the spine. An exception was demonstrated in 33 patients where extension increased the diameter, usually at one level. Radiologic subgroups of stenosis were found, but their clinical relationship could hardly be identified. No definite association between the degree of narrowing and clinical symptoms was found. CONCLUSIONS: A clinical picture is demonstrated in 100 patients with symptomatic lumbar spinal stenosis. Different types of stenosis are found radiologically, but their clinical relationships are not identified. The radiologic changes were more extensive than expected from the clinical picture, and the degree of narrowing did not correspond to the degree of clinical affliction.

Adolescent↗
PubMed1995

Cell-type specific, coordinate expression of two ADP-glucose pyrophosphorylase genes in relation to starch biosynthesis during seed development of Vicia faba L.

Several cDNA clones encoding two different ADP-glucose pyrophosphorylase (AGPase, EC 2.7.7.27) polypeptides denoted VfAGPC and VfAGPP were isolated from a cotyledonary library of Vicia faba L. Both sequences are closely related to AGPase small-subunit sequences from other plants. Whereas mRNA levels of VfAGPP were equally high in developing cotyledons and leaves, the mRNA of VfAGPC was present in considerable amounts only in cotyledons. During development of cotyledons, both mRNAs accumulated until the beginning of the desiccation phase and disappeared afterwards. The increase of AGPase activity in cotyledons during the phase of storage-product synthesis was closely followed by the accumulation of starch. The AGPase activity in crude extracts of cotyledons was insensitive to 3-phosphoglycerate whereas the activity from leaves could be activated more than five-fold. Inorganic phosphate inhibited the enzyme from both tissues but was slightly more effective on the leaf enzyme. There was a correlation at the cellular level between the distribution of VfAGPP and VfAGPC mRNAs and the accumulation of starch, as studied by in-situ hybridisation and by histochemical staining in parallel tissue sections of developing seeds, respectively. During the early phase of seed development (12-15 days after fertilization) VfAGPase mRNA and accumulation of starch were detected transiently in the hypodermal, chlorenchymal and outer parenchymal cell layers of the seed coat but not in the embryo. At 25 days after fertilization both synthesis of VfAGPase mR-NA and biosynthesis of starch had started in parenchyma cells of the inner adaxial zone of the cotyledons. During later stages, the expression of VfAGPase and synthesis of starch extended over most of the cotyledons but were absent from peripheral cells of the abaxial zone, provascular and procalyptral cells.

Amino Acid Sequence↗
PubMed1995

Diurnal variation of ventricular response to atrial fibrillation in patients with advanced heart failure.

Variability of ventricular rate was quantified by two measures of heart rate variability: the SD of the mean R-R interval (SDNN) and the SD of the 5-minute mean R-R interval (SDANN). In 35 patients with atrial fibrillation and advanced heart failure (left ventricular ejection fraction 20% +/- 9%, cardiac index 2.4 +/- 0.7 L/min/m2), SDNN and SDANN were compared to 13 preselected clinical and hemodynamic variables for prediction of outcome. During a 12-month follow-up period, 8 (23%) patients deteriorated clinically; 3 (9%) died, and 5 (14%) underwent heart transplantation. SDNN and SDANN correlated to the difference of the mean R-R interval between night (2 AM to 3 PM) and day (11 AM to noon) with r values of 0.62 and 0.77, respectively. From 15 preselected variables, only SDANN (chi 2 = 6.7, p = 0.01) was independently associated with survival on multivariate analysis. Dichotomized SDANN at 100 msec accurately predicted 12-month survival in 28 (80%) patients (relative risk = 9.77, p = 0.001). In conclusion, analysis of heart rate variability is useful in quantifying diurnal variation of ventricular rate in atrial fibrillation and might be useful in predicting survival in patients with advanced heart failure.

Aged↗
PubMed1995

Gap duration and location of attention focus modulate the occurrence of left/right asymmetries in the saccadic reaction times of human subjects.

Five human subjects were trained in a single target gap saccade task (fixation point offset precedes target onset, target presentation random at 4 deg to the left or right of the fixation point). Four of them produced different distributions of saccadic reaction times (SRT) for left vs right directed saccades. These asymmetries consisted mostly in different numbers of express saccades, which the subjects produced to the left and to the right side. Using different gap durations (0, 100, 200, 300 and 400 msec) and an overlap task, we found a systematic modulation of the frequency of express saccades: for the shortest and longest gap durations, and in the overlap task, express saccades tended to decline. As a consequence of this effect asymmetric SRTs became rather symmetric for these gap durations. In a gap task where the central fixation point was replaced by a peripheral attention target the occurrence of express saccades was strongly modulated by the location of the attention target relative to the saccade target: for all subjects the frequency of express saccades decreased when the saccade target occurred in the close vicinity of the peripheral attention target. This effect resulted again in clear modifications of the observed asymmetries. We suggest that the occurrence of express saccades can be influenced in a dynamic way by the permanent allocation of the subject's visual attention. Moreover, the phenomenon of direction asymmetry in the SRT distributions can be modulated by such manipulations of the attentional focus.

Adult↗
PubMed1995

Intertrial effects of randomization on saccadic reaction times in human observers.

We investigated the effect of randomizing different spatial and temporal parameters on saccadic reaction times (SRTs) in five human subjects, to explore the relative occurrence of express and regular saccades. Parameters randomized in various test sessions were: target direction (right/left), intertrial interval, fixation foreperiod and gap duration (two or three 400 msec) in gap and overlap trials. For the sake of comparison the parameters under consideration were kept constant in non-random control sessions. We found that express saccades were still present in the random test sessions but their relative frequency (and the number of regular saccades) obtained in a given test session depends on the type of randomized parameters: randomizing the intertrial interval or the fixation foreperiod in the gap task yielded modest but significant changes in the SRT distributions, express and fast regular saccades being present in both the control and the random conditions. Randomization of the fixation foreperiod in the overlap task, on the other hand, caused a quite drastic increase in the SRTs. Randomization of gap and overlap trials did not cause considerable effects on express and fast regular saccades in the gap trials, and the SRTs in the overlap trials were significantly increased only in two subjects. When two or three gap durations were randomly interleaved, we found effects that ranged from "negligible" (usually for the longest gap in a given test session) to highly significant differences as compared with the corresponding control condition. The results suggest that express saccades--as fast regular saccades--are visually guided saccades which occur when a certain state of saccade preparation has been reached before target onset. This state depends on the amount of activation in the brain structures involved in the control of attention and fixation, and the decision processes involved in saccade preparation.

Adult↗
PubMed1995

Comparison of PCDD and PCDF concentrations after aerobic and anaerobic digestion of sewage sludge.

The anaerobic stabilization of raw sludges of different origin was investigated. Precursors like chlorophenol and chlorobenzene isomers were added to some of the samples. The change of the PCDD/F concentrations as well as the change in the pattern of the isomers and congeners was independent of the type and amount of the added precursor. With respect to the change of the PCDD/F concentrations the digestion properties were typical in each digestion series but not applicable to other digestion processes. The quality of the digestion was characterized by measuring the change of pH, controlling the biogas flow rate and the determination of the mineralization degree. The added chlorobenzenes and chlorophenols were almost completely degraded. The aerobic digestion occurred in ventilated batch reactors leading to a significant degradation of all PCDD/F homologues. The degradation ratio depends on the origin of the sewage sludge. Independent of origin individual congeners were partially or completely degraded.

Aerobiosis↗
PubMed1995

Laparoscopic excision of a urachal cyst.

OBJECTIVES: To determine the role of laparoscopic surgery in the treatment of urachal disorders. METHODS: A case report and literature review of laparoscopic urachal cyst procedures. RESULTS: A 21-year-old man presented with a draining sinus at the umbilicus. A diagnosis of a urachal sinus was made. The patient underwent a laparoscopic excision of the sinus and cyst. CONCLUSIONS: Minimally invasive techniques such as laparoscopic surgery are the preferred means of managing urologic diseases such as the urachal cyst.

Adult↗
PubMed1995

Presaccadic processes in the generation of pro and anti saccades in human subjects--a reaction-time study.

It has been widely acknowledged that the generation of anti saccade, ie a saccade towards the direction opposite to that of a visual stimulus, requires the correct function of special brain structures. In the present study attempts were made to measure the time consumption of brain processes preceding the execution of pro and anti saccades. The saccadic eye movements of five adult human subjects were investigated in a series of combined pro/anti saccade tasks with the aid of the gap and the overlap paradigms. The type of trial--pro saccade and anti saccades--was defined by the structure of the stimulus. In some sessions the subjects were, in addition, preinformed about the actual command by a cue at different lead times before stimulus onset. Pro-saccade and anti-saccade trials were randomly intermixed in equal proportions. High error rates (> 30% of all trials in some subjects) occurred in the test sessions without preinformative cues. These errors had long reaction times (approximately 200 ms), whereas the latencies of correct pro or correct anti saccades were even longer (approximately 350 ms). Analysis of the errors revealed that they were related to the situation in the previous trial: a correct response in the previous trial enhanced the chance of making a saccade of the same type in the actual trial by up to 30%. This pretrial effect occurred whether the actual trial was a pro-saccade or an anti-saccade command. With a cue lead time of 100 ms the numbers of errors decreased, but the latencies of the correct pro or anti saccades were about 70 ms longer than those obtained in the nonrandom control. With a 200 ms cue lead time the reaction times corresponded to those in the control condition. The results suggest that the situation in a given trial creates a kind of default program for the saccade preparation in the next trial. When a cue about the actual command is given early enough, the default program is overridden correspondingly. The perception of the cue and the programming of the corresponding saccade take an additional 150 to 200 ms.

Adult↗
PubMed1995

Orally active endothelin receptor antagonist BMS-182874 suppresses neointimal development in balloon-injured rat carotid arteries.

Vascular smooth muscle cell (SMC) proliferation is an important component in the development of restenosis. Because endothelin (ET) has been reported to act as an SMC mitogen, we postulated that the orally active ETA receptor antagonist BMS-182874 would suppress the development of the intimal lesion that develops in rat carotid arteries after balloon injury. Using cultured rat aortic SMC, we noted that ET-1-stimulated increases in [3H]thymidine incorporation were blocked by BMS-182874. To determine the effect of the drug on intimal lesion formation, we treated rats with BMS-182874 (100 mg/kg orally, p.o.) or vehicle once daily for 3 weeks, beginning 1 week before balloon injury. Two weeks after injury, drug-treated rats had a 35% decrease in lesion area and a 34% decrease in the lesion/media ratio as compared with the vehicle-treated rats. In situ hybridization (ISH) analysis of balloon-injured rat carotid arteries showed an increase in ETA receptor mRNA. These data support the concept that ETA receptor activation contributes to intimal lesion formation by promotion of SMC proliferation and suggest a potential use for ETA receptor antagonists in the amelioration of hyperproliferative vascular diseases, including restenosis.

Administration, Oral↗
PubMed1995

Oxygen radical generation and acute pancreatitis: effects of dibutyltin dichloride/ethanol and ethanol on rat pancreas.

Recent studies suggest that enhanced release of free oxygen radicals plays an important role in the pathogenesis of acute pancreatitis. Therefore, we studied the activity of the oxygen radical generating xanthine oxidase (XOD) in pancreatic tissue from rats treated with either dibutyltin dichloride/ethanol (DBTC/EtOH: 6 mg kg-1/13.7 mg kg-1, i.v.), ethanol alone (EtOH: 13.7 mmol kg-1, i.v.), or isotonic saline (NaCl) as control. We also investigated activities of the oxygen radical scavengers superoxide dismutase (SOD) and glutathione peroxidase (GPX). In addition, levels of the lipid peroxidation marker malondialdehyde (MDA) were determined. Enhanced activity of XOD was not detected. While SOD activity 1 and 6 h after treatment was significantly more reduced by DBTC/EtOH than by EtOH alone, no difference was found thereafter. Correspondingly, both regimens diminished GPX activity. Moreover, DBTC/EtOH and EtOH rapidly increased MDA levels within 1 h, indicating release of oxygen radicals early on after administration. After 16 h the MDA concentration was still elevated only in the DBTC/EtOH group. Although similar metabolic alterations were observed in both groups, only DBTC/EtOH induced acute interstitial pancreatitis within 24 h. We conclude that (a) a tissue imbalance between oxidants and antioxidants might be of importance in the pathogenesis of DBTC/EtOH-induced acute interstitial pancreatitis; (b) although EtOH increases oxygen radical levels, additional damage is required for development of acute pancreatitis; (c) XOD does not seem to be responsible for significant oxygen radical generation; and (d) the DBTC/EtOH model is a useful tool to study acute interstitial pancreatitis in rats.

Acute Disease↗