RE-EXAMINATION OF INFLUENCE OF MUSCLE LENGTH ON MYOCARDIAL PERFORMANCE

Length-dependence of activation accounted almost entirely for the dependence of tension production on muscle length over the ascending limb of the length-tension relation in isolated [frog, rat, cat and rabbit] papillary muscles. If the inotropic state of the muscle was equated with the degree of activation of the contractile system, then muscle length influenced inotropic state and a change of muscle length must be regarded as an inotropic intervention. If these results were applicable to the intact heart, then diastolic volume and inotropic state could not be regarded as independent regulators of cardiac output.