Phasic Dimensional Changes in the Left Ventricle

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Abstract
The following left ventricular (LV) dimensions were followed in 43 dogs during varying experimental conditions : circumference, opicardial segment lengths, myocardial longitudinal segment lengths in various orientations, internal length of the LV outflow tract, LV pressure, systemic arterial pressure. The data show that it was an asynchronous shortening of the LV inflow tract which raised LV pressure and elongated other dimensions during the isovolumic contraction phases of LV systole. During the isovolumic period the closed mitral valve must have been « tilted » toward the apex and the septum from a relatively fixed hinge point close to the root of the aorta. Changes of LV dimensions and pressures during the isovolumic phase must have been caused primarily by rapid shortening of papillary muscles and inner layers of LV wall. LV circumference and outflow tract length shortened during the ejection phase. The data suggest that the mechanical performance of the left ventricle is not so much determined by its cavity volume or pressure at the end of diastole, but rather by processes within the ventricular wall that take place during the isovolumic contraction phase.