Myocardial Force-Velocity Relations Studied in Intact Unanesthetized Man*

13 conscious human subjects (7 men, 6 women), aged 16 to 55 years, who had previously undergone corrective cardiac operations (ASD closure, VSD closure, pulmonary valvulotomy, mitral commissurotomy, or valve replacement) during which silver-tantalum markers were sutured to their ventricles.

Various physiological and pharmacological interventions including intravenous infusions of methoxamine, isoproterenol (average 2.5 µg/min), or norepinephrine (average 25 µg/min); impeding venous return via a balloon inflated in the inferior vena cava; and altering heart rate via electrical stimulation.

Baseline control measurements obtained prior to each specific intervention.

Instantaneous myocardial force-velocity relations (velocity of shortening and intraventricular pressure measured at the isolength point).surrogate