Ventricular Response to a Pressure Load

The response of the left ventricle of the anesthetized dog to graded proximal aortic obstruction was expressed as a ventricular "pressure-function" curve relating peak ventricular pressure to end-diastolic ventricular pressure. Indices were suggested for numerical representation of the pressure-function curve and the normal variations of such indices in the same animal were defined. Pressure-function curves were found to be reproducible in the same animal during changes of cardiac output induced by arteriovenous fistulae or hemorrhage, but not after prolonged ventricular distention by high pressure loads. Changes of the pressure-function curves in both open-chest and closed-chest dogs paralleled changes of ventricular contractility which were expected during anoxia or the action of metaraminol, and which were measured in some experiments by strain-gauge arch or "flow-function" (Starling) curves. A theoretical basis for this relation of the pressure-function curve to ventricular contractility was discussed.