Pressure segment length analysis of right ventricular function: influence of loading conditions.

The purpose of this study was to determine whether segment lengths measured from the right ventricular inflow and outflow tract regions of the right ventricle would accurately reflect true volume changes of the right ventricle and to determine the response of the right ventricle to afterload increases induced by both constricting the pulmonary artery (PAC) and embolizing the pulmonary circulation with glass beads (GBE). Three excised hearts were instrumented with segment-length crystals attached to the inflow and outflow tract regions, and saline was instilled into a balloon implanted inside the right ventricular cavity. The experiments showed a high correlation (r greater than or equal to 0.90 in all cases) between static segment lengths and volume instilled. In open chest, open pericardial canine experiments, vena caval occlusion reduced end-diastolic segments lengths and right ventricular systolic pressure consistent with a reduction in right ventricular end-diastolic volume. In a separate group of animals, volume loading with dextran increased inflow and outflow end-diastolic segment lengths and increased cardiac output. In two further groups of animals, one of which was pretreated intravenously with propranolol (Inderal), both forms of pressure overload increased end-diastolic lengths in both regions. However, GBE increased right ventricular stroke work compared with PAC. We conclude that end-diastolic segment lengths reflect true volume changes of the right ventricle. Furthermore, during acute pressure overload, the right ventricle dilates to compensate for the afterload change. However, ventricular function is better maintained after GBE.