Summary
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1.
If cardiac force-velocity (PV) relationships are determined in a rhythmically beating isolated preparation by progressively changing afterloads, the PV curves obtained exhibit a characteristic nonhyperbolic shape with an upward convexity in the force domain close to Po. It was suggested by others that this might be due to contractile element (CE) shortening against series elastic component (SEC) and/or the early decay of the active state at isometric peak tension.
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2.
The present investigation performed in isolated cat papillary muscles demonstrates that neither CE shortening against SEC nor the variation of the intensity of the active state canfully account for the nonhyperbolic shape of cardiac PV curves.
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3.
On the other hand large parts of the remaining deviation could be eliminated if the “progressive loading sequence” (PLS) was replaced for an “interpolated loading sequence” (ILS). Here, the muscle contracts under steady state conditions either isometrically or isotonically (zero load). Single afterloaded test contractions are interpolated after every 10th beat.
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4.
It is concluded that the nonhyperbolic shape of cardiac PV curves, determined by progressively changing afterloads, is the expression of at least four factors: (i) the existence of displacement dependent variation of excitationcontraction coupling (including the contraction-excitation-contraction recoupling loop), (ii) CE shortening against non CE bound SEC, (iii) a variable active state and (iiii) a fourth unknown mechanism.
Zusammenfassung
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1.
Kraft-Geschwindigkeit-(PV-)Beziehungen des Herzmuskels, die in einem rhythmisch schlagenden isolierten Präparat durch stetig wachsende oder fallende Nachbelastungen bestimmt werden, zeigen charakteristischerweise einen nichthyperbolischen Verlauf mit einer nach oben gerichteten Konvexität im Kraftbereich nahe Po. Verschiedene Autoren suchten den Grund dazu in der Verkürzung des kontraktilen Elementes (CE) gegen das serienelastische Element (SE) und/oder in dem frühen Abfall des „active state” vor dem isometrischen Spannungsgipfel.
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2.
Die vorliegenden Untersuchungen wurden an isolierten Katzenpapillarmuskeln gemacht und zeigen, daß weder die CE Verkürzung gegen das SE noch die Intensitätsvariation des „active state”voll für den nicht hyperbolischen Verlauf der kardialen PV Kurven verantwortlich zu machen sind.
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3.
Andererseits läßt sich ein beträchtlicher Teil der Restabweichung dann aufheben, wenn man statt einer „progressiven Belastungssequenz” (PLS) eine „interpolierte Belastungssequenz” (ILS) wählt. In diesem Fall kontrahiert sich der Muskel entweder unter isometrischen oder (nullbelasteten) isotonen Steadystate-Bedingungen. Einzelne nachbelastete Testkontraktionen werden dann nach jedem 10. Schlag interpoliert.
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4.
Es wird die Schlußfolgerung gezogen, daß der nicht hyperbolische Verlauf der kardialen PV-Kurven, die durch ein fortschreitend sich änderndes Nachbelastungsprogramm bestimmt werden, Ausdruck von mindestens vier Mechanismen ist: a) der Existenz einer längenabhängigen Variation der elektromechanischen Koppelung unter Einschluß des Kontraktions-Erregungs-Kontraktions-Rückkoppelungskreises, b) der Verkürzung des kontraktilen Elements gegen nicht CE-gebundene Serienelastizität, c) der Variabilität des „active state” und d) eines vierten, unbekannten Mechanismus.
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This work has been supported in part by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 30, Kardiologie.
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Hennekes, R., Kaufmann, R. & Steiner, R. Why does the cardiac force-velocity relationship not follow a Hill hyperbola? Possible implications of feedback loops involved in cardiac excitation-contraction coupling. Basic Res Cardiol 73, 47–67 (1978). https://doi.org/10.1007/BF01914655
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DOI: https://doi.org/10.1007/BF01914655