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Biomedical subjects

A Lutz

Publications and source records attributed to A Lutz.

At least 19 recordsLinked to original sources
PubMed2000

Adrenocortical function in patients with macrometastases of the adrenal gland.

OBJECTIVE: Metastases of the adrenal gland are a frequent finding in patients with malignant tumors like bronchogenic carcinoma or breast cancer. Only limited and conflicting data on adrenocortical function in these patients are available. DESIGN: Cross-sectional study. METHODS: We investigated the impact of adrenal macrometastases on adrenocortical function in a series of 28 tumor patients using the ACTH(1-24) stimulation test and dexamethasone suppression test. Seven normal controls (Con), eleven patients without adrenal metastases (No Met), eight patients with unilateral (Uni Met) and nine patients with bilateral adrenal metastases (Bil Met) were investigated. RESULTS: The prevalence of adrenal insufficiency was low in our study population, with only two of nine patients with bilateral metastases having subclinical adrenocortical insufficiency. In the remaining patients with uni- or bilateral metastases, baseline and stimulated cortisol concentrations were higher than in controls and cancer patients without metastases (baseline cortisol (in nmol/l): Con: 307+/-33.2 vs Uni Met: 440+/-53.5, and Bil Met: 637.6+/-92.1, P=0.04 by ANOVA; cortisol 60 min after ACTH(1-24): Con: 794.6+/-41.2 vs Uni Met: 990.8+/-92.9, and Bil Met: 1151.4+/-155.5, P=0.03 by ANOVA). Simultaneously, baseline and stimulated serum aldosterone concentrations were significantly blunted in the tumor groups. CONCLUSIONS: Adrenal insufficiency is infrequent and develops only in patients with bilateral metastases. However, the majority of patients have activation of the hypothalamic-pituitary-adrenal axis despite adrenal metastases with strongly elevated cortisol concentrations.

Adrenal Cortex↗
PubMed1999

[Micro-CT. Technology and application for assessing bone structure].

The strength and fracture resistance of bone is determined by the structure of the trabecular network and the cortical shell. While standard 2D techniques like histomorphometry are inadequate to assess the 3D nature of the trabecular network, isotropic 3D datasets of this network can be acquired with the new imaging modality of microCT. However, so far the quantitative analysis of the generated datasets, in particular the extraction of appropriate parameters describing the bone structure, has not been finally solved. In this article we describe the technology and applications of microCT systems relevant in the field of osteology. The most important technical features of current microCT systems in this context are: 1. A spatial resolution down to 5-10 microns can be achieved. 2. The maximum sample size is related to the desired resolution by a factor of approximately 1000, that is, a resolution of 10 microns limits the maximum sample size to approximately 1 cm. 3. Scan times for microCT systems vary between minutes and hours. Currently five areas for the application of microCT systems in osteology can be identified: 1. The search of parameters characterizing the 3D trabecular structure. 2. The application of finite element models to determine the biochemical competence of the structural parameters. 3. The use of microCT in preclinical trials to study drug effects in small animals. 4. The validation of analysis methods used in high-resolution in-vivo imaging systems. 5. The 3D quantification of modeling and remodeling processes.

Adult↗
PubMed1999

A neural network model of general olfactory coding in the insect antennal lobe.

A central problem in olfaction is understanding how the quality of olfactory stimuli is encoded in the insect antennal lobe (or in the analogously structured vertebrate olfactory bulb) for perceptual processing in the mushroom bodies of the insect protocerebrum (or in the vertebrate olfactory cortex). In the study reported here, a relatively simple neural network model, inspired by our current knowledge of the insect antennal lobes, is used to investigate how each of several features and elements of the network, such as synapse strengths, feedback circuits and the steepness of neural activation functions, influences the formation of an olfactory code in neurons that project from the antennal lobes to the mushroom bodies (or from mitral cells to olfactory cortex). An optimal code in these projection neurons (PNs) should minimize potential errors by the mushroom bodies in misidentifying the quality of an odor across a range of concentrations while maximizing the ability of the mushroom bodies to resolve odors of different quality. Simulation studies demonstrate that the network is able to produce codes independent or virtually independent of concentration over a given range. The extent of this range is moderately dependent on a parameter that characterizes how long it takes for the voltage in an activated neuron to decay back to its resting potential, strongly dependent on the strength of excitatory feedback by the PNs onto antennal lobe intrinsic neurons (INs), and overwhelmingly dependent on the slope of the activation function that transforms the voltage of depolarized neurons into the rate at which spikes are produced. Although the code in the PNs is degraded by large variations in the concentration of odor stimuli, good performance levels are maintained when the complexity of stimuli, as measured by the number of component odorants, is doubled. When excitatory feedback from the PNs to the INs is strong, the activity in the PNs undergoes transitions from initial states to stimulus-specific equilibrium states that are maintained once the stimulus is removed. When this PN-IN feedback is weak the PNs are more likely to relax back to a stimulus-independent equilibrium state, in which case the code is not maintained beyond the application of the stimulus. Thus, for the architecture simulated here, strong feedback from the PNs onto the INs, together with step-like neuronal activation functions, could well be important in producing easily discriminable odor quality codes that are invariant over several orders of magnitude in stimulus concentration.

Animals↗
PubMed1997

[What are you doing when you are doing nothing? ERP components without a cognitive task].

Two experiments, an "active" and a "passive" oddball-paradigm (1. phase) with visual and auditive stimuli were performed. In both, two stimuli with a probability of 0.7/0.3 were presented. The oddball-sequence was replaced in the 2. phase without knowledge of the subjects by a sequence, in which only targets were presented. One group of the subjects has got an active task (counting the rare stimulus), the other group was told to view the stimuli passively. The rare stimulus in the oddball-sequence evoked a larger parietal P3, the auditive stimulation additionally a larger fronto-central N1 and the visual stimulation a larger central P2. The non-expected change into the 2. phase resulted in a reverse of the ERP-lateralization between 150-300 ms: Before the change of the probability the amplitudes were more negative left than right, thereafter more negative right than left. All components and effects in the active task maintained without task, but they decreased. The differences were larger with the visual stimuli. These results suggest, that the passive paradigm could be applied to patients with motoric deficits. From a theoretical point of view these results lead to certain difficulties in the interpretation of the functional importance of the P3. It can be explained better by the context-closure theory (Desmedt, 1980; Verleger, 1988) than by the context-updating theory (Donchin, 1981).

Adult↗
PubMed1995

An ocular model of Adenovirus type 5 infection in the rabbit.

Adenoviruses are a common cause of viral eye disease in humans. Recently, new antiviral drugs have been developed, which possess promising anti-adenovirus activity. In order to test these drugs, an ocular model of adenovirus infection was developed in 10 Hollander rabbits following topical, intrastromal and subconjunctival inoculation with a standard laboratory serotype (Adenovirus type 5 from The American Type Culture Collection). Clinical signs of infection-conjunctivitis, keratitis, corneal edema, subepithelial opacities, anterior chamber reaction and iritis-were evaluated. Adenovirus was isolated from the eye several days after inoculation and intra-epithelial viral replication was detected using the replica-technique. Reproducible ocular infection was clinically demonstrated in all rabbits.

Adenine↗
PubMed1993

Instrument development in the measurement of unsupported arm exercise endurance in normal adult subjects.

Many daily activities, from basic grooming to employment tasks, require adequate unsupported arm endurance (UAE). We developed an electromechanical device to measure UAE endurance. The purpose of this study was to standardize the instrument for two rates of arm motion, moderate and slow, in 18 normal adult subjects (FEVI = 3.7L +/- .78, FVC = 4.2L +/- .74, FEV1/FVC = 1.1 +/- .08). Exercise endurance limits, and the following metabolic, ventilatory, and sensation responses were determined at rest prior to exercise and at end-exercise limits for both rates of UAE:minute ventilation (Ve), tidal volume (VT), respiratory rate (RR), duty cycle (Ti/Ttot), oxygen uptake (VO2), carbon dioxide production (VCO2), inspiratory flow (VT/Ti), heart rate (HR), and visual analog scale measurements (VAS) of dyspnea (D), respiratory effort (RE), and arm fatigue (AF). Significance increases from baseline rest were shown at the endurance limits for both rates of UAE in: VO2, VCO2, Ve, VT, RR, VT/Ti, HR, VAS-D, VAS-RE, and VAS-AF. There were no changes in Ti/Ttot and SaO2 with UAE. Peak VO2, RR, Ve, VT/Ti, and VAS-D with moderate exercise were significantly greater than slow UAE; and there was a trend increase in peak HR for moderate as opposed to slow rate UAE. Despite these differences, the endurance time between the two rates of UAE were similar. These data provide standards against which UAE in COPD can be evaluated.

Adult↗
PubMed1992

Immunogenicity of a mammalian cell-derived recombinant human growth hormone preparation during long-term treatment.

The development of anti-human growth hormone (anti-hGH) and anti-host-cell protein antibodies to recombinant hGH (rhGH) of mammalian cell origin was determined in 395 children (304 GH deficiency; 91 Turner syndrome) undergoing long-term treatment (up to 54 months) for growth disorders. In all patients, blood samples were obtained prior to and every 2-3 months during treatment, and analyzed at a central laboratory for anti-hGH antibodies by RIA and antibodies to host-cell antigens by ELISA. During the first 24 months of treatment, 9 (3%) of the 304 patients with GH deficiency developed antibodies to rhGH for longer than 3 months. However, persistent antibodies were seen in only 2 patients, both of whom had proven hGH-N gene defects. In the remaining 7 (2%) anti-rhGH-antibody-positive patients, antibody concentrations showed a tendency to increase for 3-12 months, irrespective of the time of onset of measurable concentrations, and declined thereafter. In these patients, binding capacities were between 0.01 and 0.1 mg/l, and binding affinities were between 7 x 10(8) and 8 x 10(9) l/mol. Height velocity was unaffected in these children. None of the 91 patients with Turner syndrome developed persistent anti-hGH antibodies. Further, no child developed antibodies to host-cell antigens during treatment with rhGH of mammalian cell origin.

Adolescent↗
PubMed1991

New ether oxime derivatives of erythromycin A. A structure-activity relationship study.

The discovery of roxithromycin is the result of a rational and scientific process, based on the fact that at least one reason for erythromycin A's resorption variability after oral administration was its instability in the gastric juice. This instability is due to the reactivity of the ketone in position 9 in acidic medium and one chemical approach was to mask it by an oxime function. Both stereoisomers of this oxime were isolated. Direct O-alkylation of this oxime allowed access to various ether oxime derivatives and of the latter the E stereoisomers were more interesting than the Z ones. The choice of the nature of the oxime substitution was made according to the lipophilic or hydrophilic character of the aliphatic ether chain and these alterations were mainly carried out by introducing heteroatoms into this chain. These different derivatives were classified in 5 groups according to the chemical nature of the chain: Aliphatic, aromatic and nitrogen-, oxygen- and sulfur-containing chains. Two classes, those containing a nitrogen or an oxygen in the ether side chains, showed differential in vitro/in vivo antibiotic activities, with improved bioavailability. Some preliminary pharmacokinetic data confirmed this improvement and led to the selection of five candidates, from which roxithromycin emerged as the best compound.

Animals↗
PubMed1986

A new microclip for vascular occlusion. Technical note.

A new microclip for use on blood vessels 300 mu to 1 mm in diameter is described. This clip is suitable for either temporary or permanent occlusion and has been used in experimental applications. Potential clinical applications are described.

Surgical Instruments↗
PubMed1981

[Cefotaxime, syn isomer of a new methoxyimino cephalosporin with unusual activity (author's transl)].

Cefotaxime, the - syn - derivative of 7 - [(2-(2-amino-4-4-thiazolyl)-2-methoxyimino) acetamido] cephalosporanic acid, is a new semisynthetic cephalosporin. In in vitro studies, it was 80 times more active than the - anti - derivative against beta-lactamase-producing strains of Gram-negative bacteria. The range of inhibitory concentrations of cefotaxime against Gram-negative bacteria, including Haemophilus influenzae, susceptible or resistant to penicillins and cephalosporins was from 0.01 to 0.1 micrograms/ml. This activity was consistently higher than that observed with cephalothin, cephaloridine, cephalexin, and cefazolin. Nevertheless, some strains of Enterobacter cloacae were resistant. Cefotaxime showed very similar activity to that of ampicillin against group A streptococci and Streptococcus pneumoniae.

Cefotaxime↗
PubMed1978

Arsenic in sediments, water and aquatic biota from lakes in the vicinity of Yellowknife, Northwest Territories, Canada.

Arsenic concentrations were measured in aquatic invertebrates, macrophytes, sediments, and water of lakes in the vicinity of Yellowknife (N.W.T.), Canada. In arsenic-contaminated lakes the arsenic concentration ranged from 0.70 to 5.5 ppm in water, 6 to 3,500 ppm in bottom sediments, 150 to 3,700 ppm in macrophytes, 700 to 2,400 ppm in zooplankton, and less than 1 to 1,300 ppm in other invertebrates. The arsenic concentration in invertebrates varied with sampling time, place, and taxon. Arsenic concentration factors were calculated, and found to decrease with increasing concentration of arsenic in ecosystem components of the lake. No evidence was found for biomagnification of arsenic through ascending trophic levels. In high-arsenic lakes herbivores had the highest arsenic concentrations, and omnivores the lowest. Pelecypoda, Ephemeroptera, Amphipoda, and Hirudinea were conspicuously absent from high-arsenic lakes. These particular organisms may be more susceptible to the effects of arsenic than others.

Animals↗
PubMed1977

[Unexpected antibiotic properties of a cephalosporin].

The presence of an oximino group on the methylene of the (2-aminothiazol 4-yl)-acetyl side chain bound to the 7-amino cephalosporanic acid affords derivatives with syn or anti configuration. Whereas the anti isomers display low antibiotic activities, the syn isomers possess a surprising high efficiency against gram negative bacteria, enhanced a factor of 10 to 100 as compared with the cephalosporins known at the moment.

Anti-Bacterial Agents↗
PubMed1977

Experimental evaluation of HR756, a new cephalosporin derivative: pre-clinical study.

HR 756 is a new cephalosporin derivative suitable for parenteral use. The compound possesses an unusally broad spectrum of antibacterial activity especially against gram-negative bacteria. Besides Escherichia coli, Salmonella, Klebsiella, indole-negative Proteae and other species also indol-positive Proteae, Serratia marcescens, Enterobacter and many Pseudomonas aeruginosa strains are inhibited by this compound. HR 756 is stable to most of the beta-lactamases produced by gram-negative organisms. Tests on different infection models also provided evidence of the high efficacy of HR 756 in vivo.

Animals↗