Physiological loading of isolated feline cardiac muscle. The interaction between muscle contraction and vascular impedance in the production of pressure and flow waves.

Isolated cat papillary muscle preparations were assumed to contract in the wall of a hypothetical cylindrical model of the left ventricle ejecting into a vascular impedance. Using analogcomputing techniques, a feedback system was created between shortening, velocity of shortening, and the load on the muscle. This feedback function could be modulated by altering the resistance and capacitance components of the vascular impedance and by changing either muscle mass or volume of the hypothetical ventricle. For different settings of the peripheral vascular impedance, the computed flow and pressure waves generated by the model were similar to flow and pressure waves in experiments on intact hearts under analogous impedance variations. Both an increase in initial muscle length and an increased contractility augmented ventricular pressure and flow waves. A reduction in hypothetical ventricular muscle mass increased force development and mechanical power of the physiologically loaded contraction. This increased mechanical power compensated for the reduction in muscle mass in producing ventricular flow and pressure waves. A decrease in muscle force development under ventricular volume reduction decreased the mechanical power of muscle contraction and reduced ventricular pressure and flow waves. From these registrations it appeared that the sets of pressure and flow waves for a given vascular impedance, ventricular geometry, and contractile state are in direct relation to the mechanical power development of muscle contraction. Ore Res 44: 491-497, 1979