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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 53 (1975), S. 1029-1039 
    ISSN: 1432-1440
    Keywords: Biomaterials ; Implants ; Blood compatibility ; Biomaterialien ; Implantate ; Blutverträglichkeit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die Bedeutung von Implantaten zur Wiederherstellung von Körperfunktionen, die durch Krankheit, natürliche Abnutzung oder Unfall verlorengegangen sind, nimmt stetig zu. Die Grenzen, die der Anwendung von chirurgischen Ersatzteilen bei dem heutigen Stand der Technik gesetzt sind, lassen sich auf die unzureichenden Eigenschaften der Biomaterialien sowie auf konstruktive und funktionelle Schwächen der benutzten Implantate zurückführen. Die Grundlage für die Verbesserung und Neuentwicklung von Implantaten ist daher eine funktionsgerechte Konstruktion unter Berücksichtigung der besonderen Eigenschaften des Materials, das seinerseits den speziellen Anforderungen des Implantationsortes angepaßt sein muß. Für Ersatzteile im Haltungs- und Bewegungsapparat müssen Werkstoffe entwickelt werden, die weitgehend korrosions-und degracationsfest sind und hohen mechanischen Belastungen standhalten. Für Implantate im vaskulären System steht die Blutverträglichkeit deutlich im Vordergrund. Der augenblickliche Stand der Materialentwicklung läßt sich durch eine Vielzahl von Bemühungen kennzeichnen, handelsübliche Polymere durch eine besondere Oberflächenbehandlung antithrombogen auszurüsten. Eine Möglichkeit hier voranzukommen besteht darin, durch Redoxkatalysatoren aktiv in den elektrochemischen Wechselwirkungsme-chanismus an der Grenzfläche zwischen dem Werkstoff und dem Blut einzugreifen.
    Notes: Summary There is a steadily increasing importance of implants used as substitutions for body functions which have been impaired due to disease, natural abrasion or accident. With the present state of the art, the limitations for the application of surgical substitutions are due to insufficient properties of biomaterials with regard to specific applications as well as to deficiencies in design and function of the implants used. The basis for the improvement and new development of implants is therefore a functionally adequate design in which the specific properties of the material are taken into account with regard to the individual requirements of the implantation site. For orthopedic implants, materials have to be developed which are to a large extent corrosion and degradation resistant, and withstand high mechanical stress. For implants in the cardiovascular system, compatibility with blood is most significant. Present research in this field is concentrated on efforts to improve the thromboresistivity of conventional polymers by different kinds of surface treatments. One possibility is to influence actively the electrochemical interactions between material and blood components, e.g. by the use of redox catalysts.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 44 (1966), S. 396-398 
    ISSN: 1432-1440
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary We report about a simple method which is allowed to postoperativ control of the patients with implanted cardiac pacemakers without surgical manipulation. The method bases on the measurement of the heart-electrode-resistance. From the resistance-value can be judged about the present stimulation state of the heart. In addition we are able with the application of this method to recognize fauls in the artificial stimulationsystem.
    Notes: Zusammenfassung Es wird über ein einfaches Verfahren berichtet, das die postoperative Überwachung von Patienten mit implantiertem Schrittmacher ohne operativen Eingriff gestattet. Das Verfahren beruht auf der Messung des Elektroden-Myokard-Widerstandes. Aus dem ermittelten Widerstandswert kann auf die bestehenden Reizverhältnisse geschlossen werden. Darüber hinaus eignet sich die Methode zur Differenzierung eventuell auftretender Störungen am künstlichen Reizsystem.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: OSSWALD, S., et al.: Closed-Loop Stimulation Using Intracardiac Impedance as a Sensor Principle: Correlation of Right Ventricular dP/dtmax and Intracardiac Impedance During Dobutamine Stress Test. Changes of the unipolar right ventricular impedance during the cardiac cycle are related to the changing content of blood (low impedance) and tissue (high impedance) around the tip of the pacing electrode. During myocardial contraction, the impedance continuously increases reaching its maximum in late systole. This impedance increase is thought to correlate with right ventricular contractility, and thus, with the inotropic state of the heart. In the new Inos2 DDDR pacemaker, integrated information from the changing ventricular impedance (VIMP) is used for closed-loop regulation of the rate response. The aim of this study was to analyze the effect of increasing dobutamine challenge on RV contractility and the measured impedance signals. In 12 patients (10 men, 68 ± 12 years) undergoing implantation of an Inos2 DDDR pacemaker (Biotronik), a right ventricular pigtail catheter was inserted for continuous measurements of RV-dP/dtmax and simultaneous VIMP signals during intrinsic and ventricular paced rhythm. Then, a stress test with a stepwise increase of intravenous dobutamine (5–20 μg/kg per min) was performed. To assess the relationship between RV contractility and measured sensor signals, normalized values of dP/dtmax and VIMP were compared by linear regression. There was a strong and highly significant correlation between dP/dtmax and VIMP for ventricular paced (r2= 0.93) and intrinsic rhythm (r2= 0.92), although the morphologies of the original impedance curves differed quite substantially between paced and intrinsic rhythm in the same patient. Furthermore, VIMP correlated well with sinus rate (r2= 0.82), although there were at least four patients with documented chronotropic incompetence. We conclude, that for intrinsic and ventricular paced rhythms sensor signals derived from right ventricular unipolar impedance curves closely correlate with dP/dtmax, and thus, with a surrogate of right ventricular contractility during dobutamine stress testing. Our results suggest that “inotropy-sensing” via measurement of intracardiac impedance is highly accurate and seems to be a promising sensor principle for physiological rate adaptation in a closed-loop pacing system.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Electrochimica Acta 13 (1968), S. 1279-1284 
    ISSN: 0013-4686
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters 16 (1965), S. 232-233 
    ISSN: 0031-9163
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 167 (1969), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 6 (1995), S. 844-848 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Recently, biomaterials research has focused on the creation of new materials. Mixing or doping of well-tried materials should aim to result in new physical or chemical properties, better tissue tolerability and improved long-term stability. We present another way of improving performance: the application of new technologies to well-known materials. The surface structure of a coating depends on the deposition technique. Hence, the transfer of, for example, sputtering technology to biotechnology may solve current problems with well-tried materials. This paper reports the influence of surface structure and area on the properties of pacemaker electrodes. Smooth electrodes were compared with porous electrodes produced by sintering and with fractal electrodes resulting from physical vapour deposition of iridium or titanium nitride. Micrographs revealed a slight enlargement of the surface area by sintering and an enormous enlargement with fractal coating. Analysis of electrochemical properties proved the advantages of fractal coating: the impedance spectra exhibited incomparable low impedances for frequencies down to 1 Hz and no after-potentials could be detected. Clinical results confirmed the superiority of fractal electrodes. The stimulation thresholds were significantly reduced, P-and R-wave amplitudes were increased, and ventricular evoked responses and monophasic action potentials were able to be measured with clarity unknown so far.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1996), S. 273-278 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: State of the art cardiovascular stent materials are a compromise between bulk properties and surface related properties. As a consequence, deficiencies in both characteristics lead to serious limitations of stenting therapy. Beside a dissatisfying X-ray visibility of current stent materials, which hinders precise angiographic control of the stent during implantation, insufficient hemocompatibility causes subacute vessel occlusions despite stringent anticoagulant medication. Additionally, bleeding complications result which further limit the therapeutical success. Therefore it is essential to develop a new coronary stent with improved material properties for the bulk of the stent and its surface. This is realized by a hybrid concept. The stent is manufactured from tantalum, having a high inherent radio-opacity. The stent is coated with amorphous silicon carbide, optimized for hemocompatibility. An appropriate deposition technology to maximize coating adhesion was developed. Amorphous silicon carbide was investigated in vitro and in vivo to assess its suitability for coronary stents.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1996), S. 393-397 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Electrophysiologic examinations as well as the electrotherapy of heart diseases require electrodes which distinguish themselves by outstanding sensing and pacing performance. Both, the sensing and the stimulation behaviour are determined by the interface between electrode and tissue. To avoid energy losses and distortions of heart signals having components down to 1 Hz, the interface's impedance has to be very small in the corresponding frequency range. Towards this goal a new coating has been developed: electrolytically deposited electroactive iridium oxide. On the electrode's surface iridium oxide forms a long-term stable reversible redox system which changes its oxidation state according to the applied potential. The decrease of impendance is demonstrated by impedance spectroscopy: the low-frequency limit is lowered by more than three orders of magnitude to a value of 0.4 Hz. The reason is the electroactivity of this material which is caused by reversible proton incorporation into the coating, as is proven by cyclic voltammetry. Due to the low interface impedance well below 1 Hz, the coated electrodes fulfil the requirements for medical applications. Outstanding sensing behaviour was shown by measuring the monophasic action potential in dogs, which is possible without any distortions.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-8256
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Type of Medium: Electronic Resource
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