In isolated hearts, the force-length relations obtained isovolumically and at end ejection were virtually identical, with end-systolic length remaining constant for a given ejection pressure.
This study demonstrates that the end-systolic force-length relation is independent of loading and equivalent to the isovolumic force-length relation, establishing a fundamental principle of ventricular mechanics.
To determine the interrelationships between ejecting and isovolumic force-length relations and the extent to which the left ventricle will shorten, data obtained in 27 isolated, servo-regulated hearts were examined. For each heart a series of contractions, variably loaded (delta L) were derived for a thickwalled sphere and normalized by the cross-sectional area of muscle and length at zero end-diastolic pressure. It was found that within the physiological range examined total and active force were essentially a linear function of initial L with respective increments or reductions in slope produced by positive or negative shifts in contractile state. The force-L relations obtained isovolumically and at end ejection were virtually identical. For a given ejection pressure, end-systolic L was constant, despite variations in filling and therefore independent of initial L and deltaL; moreover, the L to which the ventricle shortened was determined by the course of the systolic force L-relation. Thus, irrespective of loading, delta L occurs within the confines of the contractile state-dependent isovolumic force-L relation and where the latter is equivalent to the end-systolic force-length relation.
Weber et al. (Sun,) conducted a other in Left ventricular force-length relations (n=27). Variably loaded contractions vs. Isovolumic contractions was evaluated on Force-length relations. In isolated hearts, the force-length relations obtained isovolumically and at end ejection were virtually identical, with end-systolic length remaining constant for a given ejection pressure.