Instantaneous Dimensional Changes of the Left Ventricle in Dogs

The cardiac cycle in dogs starts with an isovolumic period in which there is shortening of the base-to-apex length with an increase in cross-sectional area. Total shortening is about one-fourth of that in open-chest dogs. Minimal changes in base-to-apex length occur during the ejection phase, and there is a typical pattern of decrease in cross-sectional area. During isovolumic relaxation, the left ventricular base-to-apex length increases. Rapid filling is characterized by a sudden increase in cross-sectional area and is followed by a diastasis of varying lengths. Atrial systole is associated with a sudden significant increase in cross-sectional area and a decrease in base-to-apex length. The magnitude of change in cross-sectional area about the left ventricle during ejection may be used as an index of stroke volume. Our studies suggest that the ventricle contracts in an "eccentric manner," and relaxes in a "concentric fashion." Simultaneous monitoring of the instantaneous changes in cross-sectional area and circumference about the middle of the left ventricle may be used as an index of its efficiency of contraction in awake, intact dogs.