Kraft-Geschwindigkeits-Beziehungen der isotonischen Relaxation

Summary

Force-velocity relations of isotonic relaxation were studied in cat papillary muscles using isotonic afterloaded contractions. At a constant preload the peak velocity of isotonic relaxation successively rises with increments of after-load. It becomes maximum at loads of 30% ofP ₀, then declines and becomes zero at the maximum isometric tension. Increasing the preload force-velocity relations of isotonic relaxation are shifted upwards and to the right. At preloads more thanL _max, however, force-velocity curves of relaxation are depressed again at each level of afterload due to a successive reduction of the peak velocity of isotonic relaxation. The relations are markedly influenced by different temperatures, various frequencies of stimulation and inotropic interventions; their typical shape, however, qualitatively remains constant. The results are being discussed as to the three-elementmodel of cardiac muscle. They give evidence for both the existence of at least one viscous property in series to the contractile element and the contribution of a parallel elastic element to isotonic relaxation velocity at high initial muscle lengths.