Contractile filament and series elastic work and power—I. Mathematical development and application to left ventricular cineangiographic measurements

Abstract

A mathematical model of the left ventricle has been developed which describes the muscle element work and power including the contractile filament stress actually borne by the contractile element ( CE) and series elastic element ( SE). The muscle element work and power are then defined in terms of standard cineangiographic pressure and geometry measurements. For a normal left ventricle, the time variations of the CE and SE power for the circumferential direction at the mid-wall has been determined. There is a rapid initial rise of CE power coincident with isovolumic systole, due to the rapid contractile filament stress development. The SE is rapidly stretched during this period and energy is stored, resulting in a negative value of SE power. CE power falls away during systolic ejection and SE power falls away becoming slightly positive, due to (a) the fall in CE power and (b) circumferential fiber shortening. During diastole, CE power falls to zero and energy stored in the SE is released. Consequently, SE recoils with a rapid velocity of shortening and exhibits a peak positive power. The CE (which is now passive) is rapidly stretched during this period and exhibits a peak negative power value. Finally, both CE and SE return to their original lengths, velocities fall to zero and there is no further power produced during the latter phase of diastole.