Cardiac muscle mechanics and ventricular performance: force and time parameters

¹ Department of Pathology, Yale University School of Medicine, New Haven, Connecticut, and Department of Medicine, Columbia College of Physicians and Surgeons, New York City

Studies were designed to determine parameters of force and velocity derived from isolated cardiac muscle mechanics which would permit comparison with related performance characteristics in the intact ventricle. In the papillary muscle, for a wide range of resting muscle lengths, tension developed isometrically (Po) was found a linear function of initial muscle length and proportional to the extent of isotonic shortening (L). Length-tension curves obtained isotonically were virtually identical to those obtained isometrically. In the intact heart stroke volume is a function of L. Ventricular end-diastolic pressure is a function of resting muscle length. As increments of resting muscle length increased L, increasing ventricular end-diastolic pressure augmented stroke volume. Increasing the load carried by the muscle (afterload) at a given resting muscle length increased work performed by the papillary muscle. Similarly, increasing aortic pressure increased stroke work for a given ventricular end-diastolic pressure in the intact heart. In the papillary muscle time to maximal L was an inverse function of maximal velocity of shortening (V_max), but independent of both Lr and afterload. The inverse relation of time to max L and V_max were shown for norepinephrine and frequency. In the intact heart time to peak ventricular pressure, was found to be largely independent of ventricular end-diastolic and aortic pressures and inversely related to the inotropic state of the myocardium. Contractility of the papillary muscle strictly defined by V_max and Po, was thus characterized by time to maximal L, as well as L. Contractility of the ventricle at a given ventricular end-diastolic pressure could then be defined by stroke volume and peak pressure time, which are indices of force and velocity.

Key Words: force and velocity parameters in cardiac muscle • ventricular function and cardiac muscle mechanics • force and time parameters in the intact heart • preload, afterload, and inotropism in isolated papillary muscle and intact heart

Submitted on November 7, 1963

This article has been cited by other articles:

				G. Iribe, M. Helmes, and P. Kohl Force-length relations in isolated intact cardiomyocytes subjected to dynamic changes in mechanical load Am J Physiol Heart Circ Physiol, March 1, 2007; 292(3): H1487 - H1497. [Abstract] [Full Text] [PDF]

				K. Sagawa and K. Nakayama Simulation of Heart Muscle Contraction SIMULATION, September 1, 1976; 27(3): 173 - 176. [Abstract] [PDF]