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Biomedical subjects

G Schwarz

Publications and source records attributed to G Schwarz.

At least 163 records · Page 9Linked to original sources
PubMed1987

Incorporation kinetics in a membrane, studied with the pore-forming peptide alamethicin.

The reaction of fluorescence-labeled alamethicin with unilamellar phospholipid vesicles (DOPC and DMPC) has been investigated in a stopped-flow apparatus. Clearly single exponential time functions have been observed at temperatures above the phase transition of the bilayer. This can be interpreted in terms of an essentially one-step incorporation process. The pseudo first-order forward rate is found to be quite fast, falling in a range somewhat below the diffusion controlled upper bound. The data are quantitatively very well described on the basis of a simple mechanism. This comprises diffusion of peptide into the bilayer accompanied by a more or less slower change of the secondary structure. Aggregation of the incorporated molecules at higher concentrations is indicated to be comparatively rapid.

Alamethicin↗
PubMed1987

Continuous and simultaneous monitoring of EEG spectra and brainstem auditory and somatosensory evoked potentials in the intensive care unit and the operating room.

Individual monitoring of EEG and evoked potentials is gradually becoming standard in neurosurgery: compressed power spectra during carotid endarterectomy, brainstem auditory evoked potentials (BAEP) during posterior fossa surgery, and somatosensory evoked potentials (SEP) mainly during spinal cord surgery. In this paper, a new technique is described in which EEG, BAEP, and SEP are recorded and evaluated simultaneously and continuously. This allows a better survey of different neuronal structures and systems in the brain and brainstem. First results from intraoperative and intensive care patient monitoring are reported.

Adult↗
PubMed1987

HLA antigens in chronic pancreatitis.

Since immunological and hereditary factors may be important in chronic pancreatitis, histocompatibility antigens of classes I and II were studied in 50 British Caucasian patients, after exclusion of insulin-dependent diabetics for whom HLA associations are recognised. Chronic pancreatitis was defined by at least two independent criteria, and only subjects with alcohol-related and idiopathic disease were included. In 22 patients (21 male), weekly ethanol intake had chronically exceeded 100 g (usually substantially so); the remaining 28 had idiopathic chronic pancreatitis (ICP). Twenty patients (40%) had autoantibodies, in 11 (22%) to gastric parietal cells. Nine of those with ICP (three male) had parietal cell antibody, more than expected for the age/sex distribution. There were overall increased frequencies of HLA Cw5 and B44. In ICP there were increased frequencies of HLA A25 and Cw1, and a decreased frequency of B7. In patients with alcohol-related disease there were increased frequencies of Cw5 (50.0% vs control 15.9%), B44 (54.5% vs 29.4%), and DR4 (61.1% vs 33.6%). The increased frequency of Cw5 in alcohol-related disease alone remained significant after correction (p less than 0.05). A hypothesis that hereditary and possibly immunological factors may contribute to the aetiology of chronic pancreatitis is supported.

Alcoholism↗
PubMed1987

[Multimodal evoked potentials and heart rate variability in comatose patients--1: Method of measuring and normal values].

Multimodal EPs and heart rate variability-measurements in comatose patients have been performed for few years at the university hospitals of Graz and Erlangen. The following data and parameters are analysed and discussed: brainstem auditory evoked potentials, mechanical evoked long-latency SEP, VEP recorded over the central and occipital region and heart rate variability (HRV). The method of data acquisition and processing is described and normative data are introduced. For the long-latency EP-components a signal-to-noise-ratio (SNR) is calculated. SNR is defined as ratio of the largest EP peak-to-peak amplitude and the mean amplitude (standard deviation) of a period prior to the stimulation. An unmeasurable or questionable EP is defined when SNR less than 2.6. For the vertex-SEP the following mean +/- standard deviation was obtained: SNR = 10.6 +/- 4.6; the vertex VEP was calculated with SNR = 7.0 +/- 3.0. The SNR of the bipolar recorded occipitally VEP was 3.9 +/- 2.0. Heart rate variability measurements in normal persons revealed the following mean +/- standard deviation at a heart rate of 67.8/min +/- 10.8/min: HRV = 7.8% +/- 2.5%.

Brain Death↗
PubMed1987

[Acoustically evoked brain stem potentials. Prerequisites for clinical use, data quality and sources of error].

Ninety patients were subjected to brain-stem auditory evoked potential (BAEP) measurements in the intensive care unit. The data are analyzed and discussed with respect to their quality, reliability, and reproducibility. BAEPs of a quality satisfactory for diagnosis were found in 90% of the patients. About 10% of the measurements were distorted by artifacts and could not be used for diagnostic purposes. Reasons for these artifacts and problems of interpretation are discussed. Examples of single BAEPs and on-line monitoring of BAEPs in the form of "compressed BAEPs" are shown.

Adolescent↗
PubMed1986

Thermodynamic analysis of incorporation and aggregation in a membrane: application to the pore-forming peptide alamethicin.

Interaction of the pore-forming antibiotic alamethicin with small unilamellar vesicles of dioleoylphosphatidylcholine has been studied by means of circular dichroism. The data strongly suggest that alamethicin does not bind to the surface of the vesicles but incorporates into the lipid phase to a fairly large extent. Furthermore, aggregation of the peptide in the membrane is apparent from the existence of a 'critical concentration'. Quantitative evaluation and interpretation of the data rest on a quite generally applicable thermodynamic analysis. The underlying phenomenon is treated in terms of a partition equilibrium between the aqueous and lipid media. In the bilayer phase non-ideal interactions (described by appropriate activity coefficients) as well as aggregate formation are considered. Using this approach the relevant parameters of the alamethicin-lipid system have been determined (yielding, in particular, a partition coefficient of 1.3 X 10(3) for the monomeric peptide and a critical aqueous concentration of 2.5 microM). Finally, the possible relevance of these results for the voltage-dependent gating of alamethicin is briefly pointed out.

Alamethicin↗
PubMed1986

Long-lasting EEG reactions in comatose patients after repetitive stimulation.

Twenty patients with severe head injury and a Glasgow Coma Scale of 4-6 were subjects of a multimodality EP study. After EEG recording during rest (control 1) 60 mechanical vibration stimuli and 60 visual stimuli (interstimulus interval 10 sec) were applied. Thereafter a second EEG (control 2) was measured. To quantify a long-lasting stimulated EEG alteration, control 2 was compared with control 1 on the basis of the spectral theta/beta ratio calculated from central derivations. In 50% of the patients the theta/beta ratio was changed in control 2 and therefore a long lasting stimulation effect can be assumed. Stimulus-induced cardiac alterations were also found.

Adolescent↗
PubMed1986

[Auditory evoked brain stem potentials--possibilities and problems in the intensive care unit].

BAEP can be recorded under anesthesiologic intensive care conditions. The method does not depend on the patient's state of consciousness and is noninvasive. Observations of the course and topodiagnosis are also possible, as is an assessment of the depth of coma. The sensitivity to centrally active drugs and metabolic influences is comparatively low. For recording and evaluation of signals the specific conditions in an intensive care unit have to be taken into account, with regard to both the patients as well as the technical equipment. Continuous monitoring with so-called "compressed" BAEP broadens the scope of acute diagnosis of brain stem lesions.

Acoustic Stimulation↗
PubMed1985

[Reconstruction of the sitting position in automobiles by microtrace analysis].

Three car accidents are described in which microtrace analysis was of special significance in the clarification of the seating positions. In all three cases the occupants were under the influence of alcohol. In each case the accident occurred at night and without witnesses. The pattern of injuries in two cases was non-specific. In the first case, no fiber traces were visible to the naked eye; in the other two the fibers were recognizable to the naked eye after close examination. In all three cases, the seating position was ascertained by means of fiber trace analysis.

Accidents, Traffic↗
PubMed1985

Brain death and bioelectrical brain activity.

The effect of mechanical vibration and light stimulation on the ongoing and evoked bioelectrical activity was studied in two cases with clinically defined brain death and two other patients with severe head injury, one of them with an isoelectric EEG. The importance of such stimulation sequences for the definition of brain death is discussed, with particular emphasis on mechanical vibration.

Adult↗
PubMed1985

Molecular shape and dipole moment of alamethicin-like synthetic peptides.

The peptides Boc-(L-Ala-Aib-L-Ala-Aib-L-Ala)n-OMe, with n = 2 (P10) and n = 4 (P20), have been synthesized as purely hydrophobic models of the antibiotic alamethicin, which is known to be a voltage-dependent pore former in membranes and is apparently alpha-helical in lipophilic media. These peptides were investigated in 1-octanol, a solvent which resembles the membrane environment. From dielectric dispersion studies quantitative information on the molecular shape and dipole moments could be derived. Further independent data concerning conformation and extent of aggregation of the peptides were obtained by circular dichroism and ultracentrifuge measurements. The results suggest that the peptides assume the form of elongated particles having a significant amount of ordered secondary structure and carrying a dipole parallel to the long axis. Apparently the monomeric peptide molecules undergo, to some extent, a head-to-tail aggregation which is slightly enhanced at lower temperatures. Based on the high-frequency parts of the dielectric dispersion curves the lengths, diameters, and dipole moments of the monomer particles have been determined as 22.5A, 10A, 36 D (P10) and 28.5A, 12A, 64D (P20).

Alamethicin↗
PubMed1985

Clinical relevance of long-latency SEPs and VEPs during coma and emergence from coma.

Follow-up measurements of long-latency visual (VEP) and somatosensory (SEP) evoked potentials were performed on 30 comatose patients. Twenty-seven of the patients had severe head injury, 2 had encephalitis and 1 was in a posthypoxic state. For the SEP study a mechanical vibration stimulus was used, applied 60 times at intervals of 10 sec. The same rate was used for visual stimulation. The late EP components were classified by a signal-to-noise ratio (SNR), whereby an SNR of less than 2.6 is characteristic of a questionable or unmeasurable EP and an SNR greater than 2.6 is evidence of a clearly existing EP; the clinical state was scored using the Glasgow Coma Scale (GCS); the patient outcome was assessed 6 months after the injury using the Glasgow Outcome Scale. The highest correlation (r = 0.72) was found between the clinical state, represented by the GCS, and the SEP. A similar correlation (r = 0.66) was obtained between the GCS and the vertex VEP. The occipital VEP showed no correlation. Emergence from coma and recovery was accompanied by an increase of the SEP and an increasing spread of the VEP over the whole scalp. Most patients with a clear long-latency SEP in coma had a favourable outcome; a missing or a questionable SEP indicated a poor outcome.

Adolescent↗
PubMed1985

The kinetics of unmatched and HLA-matched 111in-labelled homologous platelets in recipients with chronic marrow hypoplasia and anti-platelet immunity.

The kinetics of homologous platelets, labelled in plasma with 111In-tropolonate, have been studied in five recipients with chronic marrow hypoplasia and severe thrombocytopenia, who were refractory to platelet transfusions as a result of alloimmunization. Mean platelet life span (MPLS), recovery, plasma 111In level and splenic and hepatic uptake kinetics were studied on two occasions, one using HLA-matched platelets and the other unmatched platelets. In each case, recovery of labelled platelets at 1 h post-injection and MPLS improved with HLA matching, although this improvement was highly variable. Only two of the five subjects would have derived any significant benefit from HLA-matched as compared with unmatched platelet transfusions. It was concluded that the need exists for additional cross-matching procedures, possibly related to platelet specific antigens, in patients who remain refractory to platelet transfusion.

Adolescent↗
PubMed1985

Antimicrobial activity of clavines.

The antimicrobial activity of two clavine-type ergot alkaloids (agroclavine, festuclavine), and 16 derivatives against four human pathogenic bacteria and Candida albicans was determined. It is shown that all ergolines tested with one exception exhibit antibacterial properties against one to four bacteria species. The most active compounds are 6-allyl-6-norfestuclavine (minimal inhibitory concentration (MIC) 30 micrograms/ml against Staphylococcus aureus), 1-propyl-6-norfestuclavine (MIC 60 micrograms/ml against Escherichia coli), 6-cyano-6-norfestuclavine (MIC 250 micrograms/ml against Pseudomonas aeruginosa), and 1-methyl-agroclavine (MIC 200 micrograms/ml against Proteus vulgaris). 1-Allyl-6-norfestuclavine and 1-propyl-6-norfestuclavine showed a broad action spectrum: the growth of all four bacteria species and of Candida albicans was inhibited. The most effective antifungal compounds are 1-propyl-6-norfestuclavine and 6-cyano-6-norfestuclavine (MIC 250 micrograms/ml). Three alkaloids of different structure (codeine, emetine, quinine) are inactive up to 500 micrograms/ml against the bacteria species and C. albicans. The acute toxicity (mouse) is remarkably diminished by the modifications of the natural clavines.

Animals↗