Left ventricular force-length relations of isovolumic and ejecting contractions.
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.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004285:Dogs; D009200:Myocardial Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D016276:Ventricular Function
D011433:Propranolol; D002118:Calcium; D009638:Norepinephrine