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  • 1
    ISSN: 1432-1106
    Keywords: Motor cortex ; Exercise ; Transcranial magnetic stimulation ; Inhibition ; Paired stimuli ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Transcranial magnetic stimulation (TMS) causes the corticospinal system to become refractory to subsequent stimuli for up to 200 ms. We examined the phenomenon of paired pulse inhibition with TMS under conditions of rest, ongoing voluntary activation (isometric force generation), and at variable delays following activation (postactivation) of the wrist extensors of seven normal subjects. Paired stimuli were delivered to the motor cortex with a circular coil at 1.1 times motor evoked potential (MEP) threshold, with various interstimulus intervals. Voluntary activation caused a marked decrease in the variability of the ratio of the amplitude of the MEP evoked by the test pulse to that of the MEP evoked by the conditioning pulse. Marked inhibition of the MEP evoked by the test pulse was still present. Postactivation, however, caused a dramatic reversal of the inhibitory effect of the conditioning pulse in all subjects at interstimulus intervals ranging from 40 to 120 ms. This effect lasted for up to 10 s following the cessation of activation. MEPs to transcranial electrical stimulation were also inhibited by conditioning TMS, but postactivation did not reverse this inhibition, indicating that the reversal of paired pulse inhibition is intracortical. We conjecture that paired pulse inhibition reflects activity of inhibitory interneurons or inhibitory connections between cortical output cells that are inactivated in the postactivation state.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    HNO 47 (1999), S. 947-956 
    ISSN: 1433-0458
    Keywords: Schlüsselwörter Stenosen der oberen Atemwege ; Lokaler Widerstand ; Körperliche Belastung ; Key words Upper airway stenoses ; Local resistance ; Exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary In benign laryngotracheal stenosis the amount of respiratory deterioration rather than the crude morphologic appearance will determine whether or not surgical measures such as dilatation or resection should be applied. This review focusses on currently available and newly developed diagnostic tools to assess the functional importance of central airway obstruction. After an outline of upper airway physiology is formulated, spirometric measurements at rest are collected. Among these, Peak Expiratory Flow Rate (PEF) proved to be the simplest and most reliable parameter to monitor an obstructing lesion of the upper airways. A novel technique for fibrobronchoscopic assessment of glottic and tracheal resistance is presented in detail. In contrast to usual tests of total airflow resistance which cannot distinguish between central and peripheral contributions, this test identifies the pressure-flow-relationship created exclusively by the local lesion. In serial stenoses, it indicates which is of higher clinical impact. Patients with upper airway obstruction complain of impaired exercise capacity. They tend to hypoventilate with imminent respiratory muscle fatigue. Therefore, spiroergometry may play a role in defining the point of incomplete compensation of a central load. The decision to operate will depend upon up the degree of physical capacity required to compensate for the stenosis.
    Notes: Zusammenfassung Bei der benignen laryngotrachealen Stenose entscheidet der Grad der Atembehinderung und nicht die Morphologie und Geometrie der Läsion über das bevorzugte operative oder konservative Procedere. Dieser Überblick beschäftigt sich mit konventionellen und neuentwickelten diagnostischen Möglichkeiten zur Sicherung der funktionellen Relevanz zentraler Atemwegshindernisse. Die Physiologie der oberen Atemwege wird skizziert. Die Parameter der spirometrischen Messungen werden noch einmal kurz abgehandelt. Unter diesen ist der exspiratorische Spitzenfluß (PEF) immer noch der am einfachsten zu erhebende und zuverlässigste Wert, um eine obstruierende Veränderung der oberen Atemwege zu kontrollieren. Eine neu entwickelte fiberbronchoskopische Technik zur lokalen Messung der durch Glottis- oder Trachealstenosen verursachten Widerstandserhöhung wird vorgestellt. Sie unterscheidet sich von üblichen Verfahren zur Erfassung des totalen Atemwegswiderstands darin, daß sie die zentralen Anteile der Druck-Fluß-Beziehung isoliert. Serielle Stenosen können einzeln ausgemessen und so in ihrer funktionellen Bedeutung gewichtet werden. Patienten mit einer Einengung der oberen Atemwege klagen unabhängig vom morphologischen Ausmaß der Stenose über eine mehr oder weniger eingeschränkte Belastbarkeit. Sie neigen unter körperlicher Anstrengung zur Hypoventilation. Dieser Punkt des unvollständig kompensierten zentralen Widerstands kann mithilfe der Spiroergometrie bestimmt werden. Er signalisiert möglicherweise die bevorstehende Ermüdung der Atemmuskulatur. In Zukunft wird die Operationsentscheidung auch an die Frage gebunden werden müssen, ob und bis zu welcher körperlichen Belastung ein Patient die zentrale Stenose respiratorisch kompensiert.
    Type of Medium: Electronic Resource
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