Left ventricular performance and its systolic mechanical properties

Abstract

The myocardium is a viscoelastic material whose mechanical properties are reflected in the pum** behavior of the ventricular chamber. Hence, the relationships between left ventricular (LV) pressure, volume, and flow may be characterized in terms of the chamber mechanical properties, elastance and resistance which are phenomenological descriptors of the observed behavior between pressure and volume and pressure and flow, respectively. For example, during the isovolumic phase of systole, the ability of the ventricle to generate pressure is expressed by the degree to which elastance increases, while during the ejection phase instantaneous LV pressure depends on both instantaneous volume (elastic behavior) and flow (resistive behavior). From the onset of systole to the end of ejection the following observations have been made; (a) ventricular elastance can be represented by a third order polynomial in time, (b) elastance is only sensitive to variations in contractile state and (c) ventricular resistance can be uniquely quantified as a linear function of LV pressure. Accordingly, a mathematical model which equates the pressure generated within the LV to the sum of the resistive and elastic components has been found to adequately describe ventricular dynamics. Using this model, it is possible to calculate the intrinsic mechanical properties of the LV from measurements of LV pressure, flow and volume obtained over a single cardiac cycle. These properties may prove useful in quantifying the functional state of the LV.