Ventricular performance and energy of compression, power, and rate of change of power during isovolumic contraction.

During isovolumic contraction, there is a calculabe compression of the blood within the ventricle. Energy is expended by the ventricle during isovolumic contraction, and some of it is transferred to the blood in the form of elastic compression. The rate of energy transfer (power) and acceleration of energy transfer (rate of change of power) during isovolumic contraction were calculated based upon considerations of the energy of compression. In anaesthetized dogs, the isovolumic energy of compression was 42 plus or minus 6 (mean plus or minus SE) dyn cm; peak isovolumic power was 1,400 plus or minus 300 dyn cm sec-1; and peak rate of change of power was 56,000 plus or minus 15,000 dyn cm sec-2. During states of augmented contractility induced by isoproterenol, the peak acceleration of energy expeniditure (peak rate of change of power) increased to 126,000 plus or minus 33,000 dyn cm sec-2 (p smaller than 0.001). Conversely, with a reduction of contractility induced by propranolol, the peak isovolumic rate of change of power decreased to 30,000 plus or minus 5,700 dyn cm sec-2 (p smaller than 0.001). The peak rate of change of power was unaffected by changes of the afterload. A trend, however, suggests that it may be affected by preload. The derivations of the isovolumic energy of compression, power, and rate of change of power are based upon firm principles of fluid dynamics. No assumptions related to ventricular geometry, synergy of contraction, or characteristics of muscle fibers are implied. Because of its physiological meaning and the theoretical validity of its derivation, an expression such as the isovolumic peak rate of change of power, when utilized as an index of ventricular performance, would appear to be of value.