Explaining Left Ventricular Pressure Dynamics in Terms of LV Passive and Active Elastances

Abstract

There has been much characterization of the heart as a pump by means of models based on elastance and compliance. The present paper puts forward the new concept of time-varying passive and active elastance. The biomechanical basis of cyclic elastances of the left ventricle (LV) is presented. Elastance is defined in terms of the relationship between ventricular pressure and volume as d P = Ed V + Vd E, where E includes passive elastance, Ep, and active elastance, Ea. By incorporating this concept in LV models to simulate diastolic (filling) and systolic phases, a time-varying expression has been obtained for Ea, and an LV volume dependent expression has been obtained for Ep. It is proposed to use these two elastances Ea and Ep to represent the intrinsic LV properties. The active elastance, Ea, can be used to characterize the LV contractile state and represents LV pressure variation due to LV volume variation (such as during the filling and ejection phases). The passive elastance, Ep, can serve as a measure of LV resistance to filling. Furthermore, it has been demonstrated how the LV pressure dynamics (and LV pressure response to LV volume) can be explained in terms of Ea and Ep.