Abstract 11025: Ventricular Efficiency Depends Critically on Systolic Contraction Below Unloaded Equilibrium Volume
Background: Systolic left ventricular (LV) contraction below unloaded LV equilibrium volume (V0) generates restoring forces which enhance early diastolic filling, equivalent to lengthening of a spring that has been compressed below slack length. It is debated whether the LV normally contracts below V0 or if it operates above V0 the entire ventricular cycle. We investigated this in dogs and further calculated the work the myocardium spends on pure elastic deformation of the myocardial wall at different operating volumes relative to V0. This elastic work must be generated in addition to the work that moves blood in and out of the ventricle and should be as low as possible to optimize efficiency.
Methods: In 10 anesthetized open chest dogs with resutured pericardium we measured LV volume by sonomicrometry and LV and pericardial pressures during baseline, caval constriction, volume loading, dobutamine infusion, and ischemia. We assessed end systolic (VES) and end diastolic (VED) volumes. V0 was found from gradual caval constriction as the zero LV transmural pressure crossover of ED volume points. The passive LV pressure-volume operating stiffness was assessed and used to calculate the elastic work required to deform the ventricle by the mean stroke volume. This work was calculated for operating volumes below, around, and above V0.
Results: In almost all cases the LV contracted below V0. Mean VES and VED are shown in the top panel of the figure relative to V0 for each intervention. Mean passive pressure-volume relation is shown in the middle panel. The elastic work required to deform the ventricle by mean stroke volume showed a minimum for contraction below and filling above V0 (lower panel).
Conclusions: The LV contracted below and filled above V0 in the open-chest anesthetized dogs with slightly depressed function. The findings therefore suggest that also the normal LV, with presumably better contractility, operates around V0, which seems to be the most energetically efficient.
- © 2012 by American Heart Association, Inc.