INTERRELATION BETWEEN THE LENGTH OF SYSTOLE, STROKE VOLUME AND LEFT VENTRICULAR WORK IN THE DOG

Abstract

Statistical analysis of a large series of dog aortic pressure pulse contours demonstrated a rough relation between the length of systole and cycle length, and a better relation between the length of systole and stroke volume, and left ventricular work. These factors were then followed in a series of expts. in which cardiodynamics were abruptly altered. Mechanical factors which influence cardiac action alter systole duration regardless of cycle length. When arterial pressure is low, venous return adequate, and the stroke volume large, length of systole is increased. Systole is also prolonged when the heart is stimulated by ephedrine or Priscol to do more work. When aortic resistance to ejection is suddenly increased, stroke volume, work, and systole length are all reduced. The changes are not necessarily parallel, and length of systole is usually restored first. Cardiac nerve stimulation, or the ejection of epinephrine or related compounds, gives rise to a more prolonged curtailment of systole, which is independent of aortic pressure level or the stroke volume. Derived ejection curves reveal the source of this curtailment to lie in a change in form of the ejection, and work output curves.