Chapter 10. The Force-Velocity-Length-Time Interrelation of Cardiac Muscle

  1. Ruth Porter and
  2. David W. Fitzsimons
  1. Dirk L. Brutsaert

Published Online: 30 MAY 2008

DOI: 10.1002/9780470720066.ch10

Ciba Foundation Symposium 24 - Physiological Basis of Starling's Law of the Heart

Ciba Foundation Symposium 24 - Physiological Basis of Starling's Law of the Heart

How to Cite

Brutsaert, D. L. (1974) The Force-Velocity-Length-Time Interrelation of Cardiac Muscle, in Ciba Foundation Symposium 24 - Physiological Basis of Starling's Law of the Heart (eds R. Porter and D. W. Fitzsimons), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9780470720066.ch10

Author Information

  1. University of Antwerp, Antwerp

Publication History

  1. Published Online: 30 MAY 2008
  2. Published Print: 1 JAN 1974

ISBN Information

Print ISBN: 9789021940250

Online ISBN: 9780470720066

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Keywords:

  • heart muscle;
  • cardiac physiology;
  • mechanical activat;
  • cardiac muscle;
  • isotonic contraction

Summary

Phase-plane analysis of the change in shortening velocity with instantaneous length during shortening at fixed loads has permitted critical reconsideration of the relative importance of changing length and time in twitch contractions of heart muscle. With unloading techniques imposed on the shortening muscle, this force-velocity-length-time relation can also be studied at loads smaller than the preload and at almost zero load over the entire length range below lmax that is below the length where active force development is maximal. Maximal unloaded shortening velocity is independent (within 5% of maximum) of length above 87.5 % of lmax and decreases with shortening below this length in parallel with isometric peak tension if allowance is made for internal shortening of the muscle during force development due to the extension of series elastic components. Experiments in which sudden load alterations (load clamps) were imposed on the shortening muscle have demonstrated that the force-velocity-length relation is independent of time over the major portion of external shortening. Abrupt unloadings to zero load (zero load clamps) have indicated that this time independence is attained early in the course of the contraction within 10–20% of the time to reach peak tension. In afterloaded contractions, the onset of this time independence is delayed owing to the slower rise in force during the isometric phase of the contraction. The duration of this time independence is partly determined by the total load and by the length changes during shortening per se. These findings indicate that this time-independent interrelation between force, velocity and length reflects a unique state of equilibrium of the degree of activation resulting from the interaction of several variables.