Myocardial Force-Velocity Relations Studied in Intact Unanesthetized Man*

Open Access
Publisher Website
Google Scholar
Abstract
With a cine-radiographic technique, myocardial force-velocity relations were investigated in 23 studies on 13 patients at the time of postoperative cardiac catherterization. The technique consisted of exposing cine-radiograms at 30 frames/sec and measuring the velocity of movement of roentgenopaque markers that had been sutured to the external surface of the ventricles, while simultaneously recording intraventric-ular pressure. A beat-to-beat analysis of the force-velocity relationship was then accomplished by measuring the velocity and the pressure at a constant length point in each contraction. Thereby, a constant relation was established between intraventricular pressure and myocardial wall tension. When afterload was augmented with methaxamine or was decreased by impeding venous return with a balloon distended in the inferior vena cava, force and velocity varied inversely. In contrast, norepinephrine, isoproterenol, increasing heart rate by electrical pacing, and paired electrical stimulation all augmented velocity at any given pressure. Thus, in intact, conscious man, the heart displays the same reciprocal relation between velocity of shortening and generation of force observed in isolated papillary muscle, and a change in the contractile state of the human heart is manifested by a shift in the force-velocity relation.