Dynamics of the interventricular septum and free ventricular walls during blood volume expansion and selective right ventricular volume loading in dogs.

To examine whether the right ventricle responds differently to blood volume expansion and selective right ventricular volume loading, segment lengths in the interventricular septum and the free walls of both ventricles and right ventricular septal-to-free-wall-distance were measured by an ultrasonic technique in open-chest dogs. Blood volume expansion increased segment lengths at all recording sites in proportion to stroke volume. Selective right ventricular volume loading induced by opening a shunt between the pulmonary artery and the superior vena cava increased right ventricular stroke volume by 40-80%; end-diastolic segment length and myocardial shortening increased in the septum and free wall of the right ventricle whereas left ventricular stroke volume and segment length decreased. Comparison of data obtained before and after opening of the shunt indicated that changes in myocardial dynamics of the right ventricle and septum accounted for approximately 30% of the increase in right ventricular stroke volume. However, both end-diastolic dimension and systolic shortening of the right ventricular septal-to-free-wall distance were larger during right ventricular volume loading than during blood volume expansion. Thus, most of the increase in stroke volume during selective right ventricular volume loading is caused by a change in the configuration of the right ventricle.