Significance of geometrical reference models of the left ventricle for a new concept of evaluation of cardiac pumping function.

A methodological approach based on Frank's pressure-volume (P-V) diagram and model calculations for analyzing the determinants of stroke volume (SV) under conditions of altered ventricular geometrical configuration is discussed with respect to the underlying geometrical models. The approach is generalized in the sense that alterations in myocardial elasticity are considered. In addition, simplifying assumptions on which the stress-length (sigma-1) diagram in previous studies was based are now discarded. It can be shown that calculated stroke volume is only slightly affected by the choice of the models when referring to average wall stress. However, if we use the formula for midwall stress recommended by Mirsky, then the influence of the geometrical model becomes more important. Based on the example of a rat with experimental aortic stenosis in the decompensated stage it is demonstrated that this methodological approach is an indispensible completion of O. Frank's concept when evaluating ventricular dynamics, and could gain clinical significance in future.