Afterload- and preload-dependent interactions in the isolated biventricular working rat heart

The afterload- (AL) and preload- (PL) dependent interactions between the left and right ventricle (LV, RV, respectively) of an isolated biventricular ejecting rat heart were measured in terms of left (L) and right (R) intraventricular peak pressure (LP(max) and RP(max), respectively) and aortic and pulmonary flow (AF, PF, respectively).

Starting with standardized loading conditions, LVPL was varied in six steps for each of five distinct LVALs (n=28) and then RVPL was varied in seven steps for each of five distinct RVALs (n=37). Thus, the entire range of loading conditions was covered.

Identification of AL-dependent systolic interactions revealed an important DeltaLP(max)-DeltaRP(max) gain of 0.25 (r(2)=0.78) and a still more dominant DeltaRP(max)-DeltaPF gain of 0.45 (r(2)=0.84). At least 26% of maximal PF were attributable to LV systolic function. In contrast, R-L systolic interaction impeded PF; there was no global crosstalk pressure gain and no ipsilateral pressure-flow gain. Reduction of RV activity augmented AF by at least 15%. PL-dependent L-R interactions were absent except for minimal LVAL. In contrast, the reverse interaction reflected an inverse correlation between RVPL and AF, which is coincidential with other studies (-11% AF for a doubling of the standard RVPL). For the minimal RVAL, there was a biphasic response of AF to RVPL. Unloading the maximally loaded RV revealed an overall inhibition of AF by 37% for the standardized LV. Unloading the standardized RV revealed a basal inhibition of AF by 6% for the standardized LV and a 4.5% augmentation for the highly loaded LV. Consequently, basal contribution of RV to LV performance depended on the conditions of LV loading.

The authors suggest a unidirectional transseptal R-L mechanism for diastolic interactions, and transseptal L-R and paraseptal R-L mechanisms for systolic interactions.