QUANTITATIVE ASSESSMENT OF INDEPENDENT CONTRIBUTIONS OF PERICARDIUM AND SEPTUM TO DIRECT VENTRICULAR INTERACTION

In the intact animal, it is difficult to discriminate between the inde pendent effects of series and direct ventricular interaction (DI) or t he individual contributions of the pericardium and septum to DI. Left ventricular (LV) venous return (LVVR) and right ventricular (RV) end-d iastolic pressure (RVEDP) were varied independently in a right-heart b ypass model. LV minor-axis diameters were measured, and the product of the two diameters was used as an index of LV volume (LVVI). At each R VEDP (0, 5, 10, and 15 mmHg), increased LVVR caused an increased LVVI. When RVEDP was increased, increased pump output was required to maint ain a given LVVI. RV-to-LV pressure gain (Delta LVEDP/Delta RVEDP) ref lects coupling and DI. With the pericardium closed, the gain was depen dent on RVEDP; when RVEDP was increased from 0 to 5 mmHg, the gain was not statistically different from zero, indicating little or no DI. Wh en RVEDP was increased from 10 to 15 mmHg, the gain was not statistica lly different from 1.0, indicating similar to 1:1 coupling of the vent ricles. Opening the pericardium reduced the gain, but significant inte raction remained. When the septal contribution was accounted for, the remaining interaction was eliminated. In conclusion, DI substantially affects LVEDP-volume relations. Considerable increases in RV output ma y be required to counterbalance increased constraint to LV filling. Wi th the pericardium closed, RV-to-LV coupling is minimal when RVEDP is low and increases to 1:1 coupling when RVEDP is high. Opening the peri cardium reduces DI, but significant septum-mediated interaction remain s.