The Mechanical Cardiac Cycle

Shortening Time of the Internal Diameter of the Canine Left Ventricle

Abstract

Ventro-dorsal internal diameter of the canine left ventricle, the left ventricular and aortic pressure, and electrocardiogram were recorded simultaneously to measure the various systolic time intervals. Systolic time intervals related to isometric contraction time and ejection time shortened with increased heart rate and lengthened with elevation of left ventricular pressure. The onset of the shortening of internal diameter occurred 31.57±10.08 milliseconds, with a range of 0 to 48 milliseconds before the onset of the upstroke of aortic pressure. End-systole, defined as the shortest internal diameter, occurred 12.82±5.51 milliseconds, with a range of 4 to 27 milliseconds, before end-ejection, defined as the dicrotic notch of the aortic pressure. Dynamic geometry during isovolumetric contraction, the differences between the phases of end-systole and end-ejection, and the artifact of microtip manometer are discussed.