The pressure-volume relation and the mechanics of left ventricular contraction.

The left ventricle is represented as an elastic thick-walled cylinder contracting symmetrically. The force generated by the active state of the myocardium in the radial direction is represented by body force (force/unit volume) and is included in the mathematical formalism that describes the contraction of the left ventricle. An equation for the P-V relation in the left ventricle is derived and various applications to study cardiac mechanics are discussed. The results obtained tend to demonstrate that the active force generated by the myocardium during an ejecting contraction reaches its maximum value near the end of the systolic phase, when the slope E of the P-V line reaches its maximum value Em, and that it is related to the peak isovolumic pressure.