Myocardial Force - Velocity Relations Studied in Intact

In 1938, A. V. Hill demonstrated that the inverse relationship between the force generated and the velocity of shortening constitutes one of the most fundamental mechanical properties of skeletal muscle (1). More recently it has been shown that a similar reciprocal relationship between force and velocity also exists in the isolated cat papillary muscle (2-5). Moreover, at any given muscle length, various positive inotropic interventions, such as augmentation of heart rate (2, 3), administration of norepinephrine (3, 4), Ca++ (3), or digitalis (6), shift the force-velocity relation so that the velocity of shortening is greater at any given load and the maximal velocity of the unloaded muscle is increased. This type of shift in the force-velocity relation is interpreted to reflect an augmentation of the contractile state of the myocardium. The ability to alter the relationship between the force generated and the velocity of shortening in heart muscle is in contrast with the relative stability of the forcevelocity relation in skeletal muscle. Recently, studies on isolated human papillary muscle extended to man the concept that the force-velocity relation may be used to characterize the basic contractile state of heart muscle (6). Fry, Griggs, and Greenfield (7) and Levine and Britman (8) have shown in open-chest dogs that the inverse relationship between force and instantaneous velocity is applicable to the intact canine ventricle. The objective of the present investigation was to determine whether or not the intact ventricle in conscious human subjects adheres to this basic law of muscular contraction that had been elucidated in various experimental