| Summary: | <p>Abstract</p> <p>Background</p> <p>Description of the heart as a pump has been dominated by models based on elastance and compliance. Here, we are presenting a somewhat new concept of time-varying passive and active elastance. The mathematical basis of time-varying elastance of the ventricle is presented. We have defined elastance in terms of the relationship between ventricular pressure and volume, as: <it>dP </it>= <it>EdV </it>+ <it>VdE</it>, where E includes passive (E<sub>p</sub>) and active (E<sub>a</sub>) elastance. By incorporating this concept in left ventricular (LV) models to simulate filling and systolic phases, we have obtained the time-varying expression for E<sub>a </sub>and the LV-volume dependent expression for E<sub>p</sub>.</p> <p>Methods and Results</p> <p>Using the patient's catheterization-ventriculogram data, the values of passive and active elastance are computed. E<sub>a </sub>is expressed as: <graphic file="1475-925X-4-10-i1.gif"/>; E<sub>p</sub>is represented as: <graphic file="1475-925X-4-10-i2.gif"/>. E<sub>a </sub>is deemed to represent a measure of LV contractility. Hence, Peak dP/dt and ejection fraction (EF) are computed from the monitored data and used as the traditional measures of LV contractility. When our computed peak active elastance (E<sub>a,max</sub>) is compared against these traditional indices by linear regression, a high degree of correlation is obtained. As regards E<sub>p</sub>, it constitutes a volume-dependent stiffness property of the LV, and is deemed to represent resistance-to-filling.</p> <p>Conclusions</p> <p>Passive and active ventricular elastance formulae can be evaluated from a single-beat P-V data by means of a simple-to-apply LV model. The active elastance (E<sub>a</sub>) can be used to characterize the ventricle's contractile state, while passive elastance (E<sub>p</sub>) can represent a measure of resistance-to-filling.</p>
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