Evaluation of myocardial force-velocity relation in closed-chest dogs

Abstract

The force-velocity characteristics of the left ventricle in 35 closed-chest anesthetized dogs were studied by means of a strain-gauge catheter assembly. Instantaneous velocity of shortening was determined at an isolength point on the curve of fiber shortening, by drawing a tangent to the curve relating height of deflection to time. Ventricular pressure related in time to the isolength point was used as a measure of force. Instantaneous force-velocity relations at a constant muscle length could thus be studied. Alterations in afterload induced by inflating and deflating an intra-aortic balloon and by methoxa-mine led to reciprocal changes in force and velocity. Positive inotrophic drugs, i.e., epinephrine, norepinephrine, and isoproterenol, on the other hand, shifted the torce-velocity curve upwards, or upwards and to the right, indicating either an increase in velocity alone or an increase in force plus velocity, respectively. These results pointed to an augmentation of the contractile state of the heart. Beta adrenergic blockade with propranolol led to a decline of both force and velocity.