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  • 1
    ISSN: 1573-2622
    Keywords: multifocal ERG ; notch filter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The filter settings of the amplifier section of ERG recording systems have large impact on the waveforms of the recorded responses. In this study, the effects of a 50 Hz notch filter were assessed for both First-Order-Kernel- (FOK) and Second-Order-Kernel-responses (SOK 1st slice) from multifocal ERGs recorded with a VERIS III system. Amplitude and phase responses of the amplifier section were recorded for typical filter settings with the notch filter active and inactive. Multifocal ERGs (MERGs) from a group of 11 normal subjects were recorded for both amplifier settings, the waveforms resulted from those recordings were compared in the time and frequency domain. To verify the results, the recordings without the notch filter were digitally filtered with a simulated notch filter and compared to the responses recorded with an active analog notch filter. The line filter has the biggest attenuation at 50 Hz with an additional phase jump of 180°. The FOK responses of MERGs are assembled by frequencies below 65 Hz with main spectral components between 19 and 47 Hz. The 1st slice of the SOK consists of frequencies up to 100 Hz with main components between 19 and 84 Hz. Thus, if FOK recordings are to be analyzed, the notch filter of the amplifier can be used in order to cope with noise problems caused by the line frequency of 50 Hz. However, one must be aware that the attenuation of higher frequency components will lead to changes of the waveforms. For SOK analysis, main spectral components are attenuated and/or shifted in phase, which leads to completely different waveforms and severe distortion of the recording results.
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  • 2
    ISSN: 1573-2665
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 3
    ISSN: 1438-2199
    Keywords: NMDA receptors ; Glycine site ; Antagonists ; Partial agonists ; Desensitisation ; Subtypes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glycine is a co-agonist at NMDA receptors and it's presence is a prerequisite for channel activation by glutamate or NMDA. Physiological concentrations reduce one form of NMDA receptor-desensitization. Interactions between the glycineB site and other domains of the NMDA receptor are complex and include the glutamate, Mg+ and polyamines sites. Glycine shows different affinities at various NMDA receptor subtypes probably via to allosteric interactions between NMDA2 subunits and the glycine recognition site on the NMDAR1 subunit. There is still some debate whether the glycineB site is saturatedin vivo but it seems likely that this depends on regional differences in receptor subtype expression, local glycine or D-serene concentrations and the expression of specific glycine transporters. GlycineB antagonists and partial agonists have been reported to have good therapeutic indices as neuroprotective agents against focal ischaemia and trauma, anti-epileptics, anxiolytics, anti-psychotomimetics and in models of chronic pain. They clearly lack two potentially serious side effects classically associated with NMDA receptor blockade, namely neurodegenerative changes in the cingulate/retrosplenial cortex and psychotomimetic-like effects. This improved therapeutic profile may be partially due to the ability of full glycineB antagonists to reveal Gycne-sensitive desensitization and possibly also via functional and/or regional NMDA receptor subtype selectivity.
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  • 4
    ISSN: 1573-2622
    Keywords: electroretinogram ; multifocal ERG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The First Order Kernel responses (FOK) from a group of 15 normal subjects aged 21–36 yrs were recorded under clinical conditions with the multifocal ERG (MERG) systems VERIS and RETiscan using system-specific software and hardware under various parameter settings. First, the multifocal ERG's of normal subjects were recorded with the standard-parameters of VERIS and RETIscan. Thereafter the VERIS system parameters were set as close as possible to the RETIscan-setup, and the recordings were repeated. The VERIS parameters changed were the luminance- and contrast-settings of the stimulus-monitor and m-sequence-timing. In addition, the effects of different sampling rates were also examined. The consequences of the parameter changes were analyzed by displaying the peak times of the First-Order-Kernel (P1). The parameter-combinations used for recording lead to system-specific results. By varying the luminance/contrast settings and/or the m-sequence-timing the results can be changed. The amplitude of the recorded results can be influenced by the luminance-settings of the stimulus-monitor, and the topography of the P1 peak times is affected by the m-/f-frame-combination of the recording stimulus. With their standard parameters, the two systems give different measures of the P1 peak times. By adjusting the recording parameters, these differences can be reduced significantly. The main parameter here is the m-sequence-timing, although the sampling rate must also be taken into account with regard to the accuracy of the recording results.
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  • 5
    ISSN: 1572-9605
    Keywords: phase transitions ; ruthenate–cuprate ; superconducting ferromagnets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have systematically investigated the magnetic, electrical, and structural properties of the high-purity superconducting ferromagnet RuSr2GdCu2O8, in which superconductivity and significant ferromagnetism have been reported to coexist. Our results show that there may exist in this compound a novel superconducting state which is characterized by the absence of a bulk Meissner effect, the presence of negligible superconducting condensation energy, and the appearance of an unusually large effective penetration depth. Such a state appears to have a nonuniform filamentary structure existing in the less magnetic walls between the ferromagnetic domains or a fine-grain structure beset by ferromagnetic walls between antiferromagnetic “domains,” similar to the case of NdNi2B2C. These results are presented and contrasted with the recently reported Meissner effect in RuSr2GdCu2O8 in terms of the various phase transition sequences predicted.
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  • 6
    ISSN: 1432-1289
    Keywords: Schlüsselwörter Jet-Lag ; Zirkadiane Rhythmik ; Leistungstests ; psychologische ; Leistungstests ; physiologische ; Langzeitmonitoring ; Polysomnographie
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Zum Thema Die physische und psychische Beanspruchung dürfte bei keiner Berufsgruppe so extrem hoch sein wie bei Flugpiloten. Somit eignet sich dieser Personenkreis auch vorzüglich zur Ermittlung diesbezüglicher Daten. Unter der Vielzahl belastender Faktoren sind die durch ständige Überwindung von Zeitzonen gestörte zirkadiane Rhythmik und die sehr langen, oft irregulären Arbeitszeiten bei sonstiger körperlicher Immobilität am wichtigsten. Eine breit gefächerte Fülle von psychologischen, physiologischen und physiologisch-chemischen Meßmethoden dient dazu, diese Belastungen mittels entsprechender Daten zu objektivieren. Die Synopsis aller Meßergebnisse hat das Ziel, die Belastbarkeitsgrenzen rechtzeitig zu erkennen und die Flugsicherheit zu erhalten und zu verbessern.
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  • 7
    ISSN: 1432-055X
    Keywords: Schlüsselwörter Lunge ; Funktionelle Residualkapazität ; Meßmethoden ; Mechanische Beatmung ; Überblick ; Key words Lung ; Functional Residual Capacity ; Measurement techniques ; Mechanical ventilation ; Review
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract Determination of Functional Residual Capacity (FRC) can be performed through washout methods, indicator gas dilution or bodyplethysmography. Some of these techniques have been adapted for use in intensive care patients whilst being mechanically ventilated. However, most measurement setups are bulky, cumbersome to use and their running costs are high. Hence FRC measurement has not become a routine method in intensive care although it offers considerable advantages in the management of ventilated patients such as the determination of „best PEEP”, the detection of progressive alveolar collapse in the course of acute lung injury and during weaning from mechanical ventilation. Up to now most efforts to improve and simplify FRC measurement were made at the expense of accuracy. An ideal method ought to be accurate, easy to handle and cost-effective. It should supply not only FRC data but also information about intrapulmonary gas distribution and dead space. These demands can be met using modern data acquisition software. The pros and cons of all methods available for FRC measurement are discussed in view of their suitability for intensive care patients. A conventional nitrogen washout using emission spectroscopy for measurement of nitrogen concentration gives satisfying exact values for the determination of the parameters mentioned above. The measurement error can be lowered under 5% by special corrections for flow and nitrogen signal (delay and rise times, changes of gas viscosity). For flow measurement a normal pneumotachograph can be used. Using a laptop computer for data acquisition the bed-side monitor fulfills most of the demands in intensive care. It is then also possible to measure indices of intrapulmonary gas distribution such as Alveolar Mixing Efficiency and Lung Clearance Index.
    Notes: Zusammenfassung Zur Bestimmung der Funktionellen Residualkapazität (FRC) bedient man sich verschiedener Auswaschverfahren, Dilutionsmethoden oder der Bodyplethysmographie. Einige dieser Methoden konnten für die Messung bei beatmeten Intensivpatienten adaptiert werden, jedoch sind sie bis heute zu aufwendig, teuer und platzraubend. Daher hat die FRC-Bestimmung den Weg in die klinische Routine noch nicht gefunden, obwohl sie eine Reihe von Vorteilen bei der Beatmungstherapie von Intensivpatienten böte, so für die Quantifizierung restriktiver Lungenfunktionsstörungen, die PEEP-Optimierung, die Verlaufskontrolle im akuten Lungenversagen und während des Weanings. Viele Vorschläge zur Vereinfachung der Messung gingen bisher auf Kosten der Genauigkeit. Eine ideale Meßmethode müßte ausreichend genau, mit geringem Meßaufwand verbunden, weitgehend automatisiert und wenig kostenintensiv sein. Sie sollte nicht nur einen Wert für die FRC, sondern auch Informationen über das Auswaschverhalten und die Größe des Totraums liefern. Durch den Einsatz moderner Meßwertverarbeitungsprogramme scheinen inzwischen diese Anforderungen erfüllbar zu sein. Wir geben einen Überblick über die heute verfügbaren Methoden zur FRC-Messung und vergleichen sie hinsichtlich ihrer Eignung für die Intensivtherapie. Eine klassische Stickstoffauswaschmethode mit emissionsspektrometrischer Messung der Stickstoffkonzentration liefert hinreichend genaue Werte zur Ermittlung der gewünschten Parameter. Der Meßfehler kann bei entsprechender Korrektur des Fluß- und Stickstoffsignals für methodenbedingte Signalfehler (Delay- und Anstiegszeiten, Schwankungen in der Gasviskosität) unter 5% liegen. Zur Flußmessung genügt ein handelsüblicher Pneumotachograph. Bei Verwendung eines Laptops zur Datenerfassung erfüllt der bettseitig einsetzbare Meßplatz die meisten Anforderungen in der Intensivtherapie. Neben der FRC stehen auch verschiedene Parameter zur Beschreibung des Auswaschverhaltens, wie die Alveolar Mixing Efficiency und der Lung Clearance Index zur Verfügung.
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  • 8
    ISSN: 1433-0474
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 9
    ISSN: 1433-0423
    Keywords: Key words Aniridia • WAGR syndrome • PAX6 • ; Mutations • Wilms' tumor risk ; Schlüsselwörter Aniridie • WAGR-Syndrom • PAX6 • ; Mutationen • Wilmstumor-Risiko
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Hintergrund: Aniridie ist eine kongenitale okuläre Fehlbildung, charakterisiert durch vollständige oder teilweise Irishypoplasie, häufig assoziiert mit Glaukom, Mikrokornea, Katarakt, Makula- und Optikushypoplasie sowie Nystagmus. Aniridie tritt hereditär oder sporadisch auf. Die sporadischen Fälle können einen Wilmstumor (embryonales Adenosarkom der Niere) – häufig als Teil des WAGR-Syndroms (Wilmstumor, Aniridie, urogenitale Fehlbildungen und mentale Retardierung) – entwickeln. Auf Chromosom 11p13 wurde das PAX6-Gen als das Kandidatengen für Aniridie identifiziert. Genprodukt ist ein Protein, das die Transkription anderer Gene reguliert. Patienten und Methode: Für die Analyse wurden PCR (Polymerasekettenreaktion), SSCP (single-strand-conformation-polymorphism) und Sequenzierung als Technik angewendet. Ergebnisse: Bei 13 von 20 Aniridie-Patienten konnten Mutationen im PAX6-Gen nachgewiesen werden. Schlußfolgerung: Aufgrund der Mutationen kommt es zur Bildung eines Genprodukts mit eingeschränkter Funktion bzw. zu einem reduzierten PAX6 Proteinspiegel. Die molekulargenetische Analyse der Aniridie erlaubt auch eine Einschätzung des Wilmstumor-Risikos, da Patienten mit einer nachgewiesenen PAX6-Genmutation – im Gegensatz zu den Fällen großer Deletionen der 11p13-Region – kein erhöhtes Risiko tragen, einen Wilmstumor zu entwickeln.
    Notes: Introduction: Aniridia represents a congenital ocular disorder with partial or complete iris hypoplasia. The disorder is associated with poor vision, glaucoma, corneal and lenticular opacities, ectopia lentis due to abnormal zonula fibers, as well as optic nerve and macular abnormalities. Aniridia may present as either hereditary or sporadic cases. Some of the sporadic cases develop Wilms' tumor, frequently as part of the WAGR syndrome (Wilms' tumor, aniridia, genitourinary abnormalities and mental retardation). PAX6, a candidate gene located on chromosome 11p13, is often mutated in aniridia patients. The gene encodes a transcription regulatory protein. Method: Analysis of the PAX6 gene was done using PCR (polymerase chain reaction), SSCP (single strand conformation polymorphism) and DNA sequencing. Results: In 13 of 20 aniridia patients a PAX6 gene mutation was found. Conclusion: The mutations result in a gene product with reduced function or a reduced PAX6 protein level. Molecular analysis of aniridia is also a valuable diagnostic tool for Wilms' tumor risk evaluation, as patients with proven PAX6 mutations – in contrast to cases with large deletions of the 11p13 region – are at no increased risk to develop Wilms' tumor.
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  • 10
    ISSN: 1432-1440
    Keywords: Dopamine ; Levodopa ; Positive inotropic effect ; Human heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The direct positive inotropic effects of dopamine and its precursor, levodopa, were measured using isolated, contracting human papillary muscle strips taken from patients during mitral valve replacement. Levodopa did not produce any positive inotropic effect at concentrations up to 3×10−3 M. The positive inotropic effects of dopamine were observed at concentrations above 1×10−5 M with the maximal effect at 3×10−3 M — concentrations higher than those observed in therapy. This inotropic effect was reduced by the β1 antagonist, 1-practolol (1×10−6 M); the β2 antagonist, ICI 118,551 HCl (1×10−6 M); the dopamine antagonist, haloperidol (3×10−6 M); the neuronal uptake inhibitor, cocaine (3×10−5 M), but not by the α1, prazosin (1×10−7 M). This indicates that dopamine exerts its positive inotropic effects on human heart muscle mainly through release of noradrenaline, together with possible interactions at β-and dopamine-receptors. The maximal inotropic effect of dopamine was about 50% that of calcium (15 mM, 6.2±0.7 mN) or ouabain (1×10−7 M, 5.0±0.8 mN) when measured in the same muscle strips, possibly due to the reduced cardiac noradrenaline content together with the reduced β-receptor number in congestive heart failure. This concentration of ouabain (1×10−7 M) gave almost maximal inotropy without marked toxicity; when dopamine was then added, only toxicity developed without any further increases in force of contraction. Any haemodynamic benefits of dopamine therapy in optimally digitalis-treated patients are probably due to other cardiovascular effects such as vasodilatation.
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