Series viscoelasticity affects end - diastolic pressure - volume curves

It is typically assumed that the end-diastolic pressure - volume (EDPV) curve is free of time dependent viscoelastic effects and is equal to the static curve (SPV). In this study, the effects of series and parallel viscosity were incorporated into a math model to examine this assumption. The ventricle was modeled by a time and volume dependent pressure. The SPV curve was represented by an exponential function. Series and parallel viscoelastic elements were added to the basic model. Afterload was a three element Windkessel and preload was a constant pressure with flow resistance. The SPV curve was computed directly from the exponential function. The BDFV curve was determined from a vena caval occlusion, represented by slowly decreasing preload (fig.). It was found that the EDPV and SPV curves differ considerably in the low PV range. Hence, we concluded that series viscoelasticity affects EDPV.