Force-velocity-length relationship during cardiac hypertrophy. Time course of activation.

Basic mechanical properties observed during cardiac hypertrophy were studied in left ventricular rat papillary muscles after exposure to chronic pressure and/or volume overloading. It is always possible, during such overloading conditions, to define the level of contractility in terms of a force-velocity-length (F-V-L) relationship regardless of time and initial length. Thus, during a determined period of the contraction phase and for a given total load, shortening velocity remained an univocal time-invariant function of shortening length, involving a time-independent maximum intensity of activation. The onset of this precise phase was reached relatively soon after stimulus. The time-independent F-V-L relation was observed both in controls and in hypertrophied heart muscles, whatever the degree and the type of induced hypertrophy, and even during the latest phases of congestive heart failure.