Circulation Research, Vol 68, 1532-1548, Copyright © 1991 by American Heart Association

ARTICLES

Short-time-scale left ventricular systolic dynamics. Evidence for a common mechanism in both left ventricular chamber and heart muscle mechanics

KB Campbell, SG Shroff and RD Kirkpatrick
Department of VCAPP, Washington State University, Pullman 99164-6520.

Based on the premise that short-time-scale, small-amplitude pressure/volume/outflow behavior of the left ventricular chamber was dominated by dynamic processes originating in cardiac myofilaments, a prototype model was built to predict pressure responses to volume perturbations. In the model, chamber pressure was taken to be the product of the number of generators in a pressure-bearing state and their average volumetric distortion, as in the muscle theory of A.F. Huxley, in which force was equal to the number of attached crossbridges and their average lineal distortion. Further, as in the muscle theory, pressure generators were assumed to cycle between two states, the pressure-bearing state and the non-pressure-bearing state. Experiments were performed in the isolated ferret heart, where variable volume decrements (0.01-0.12 ml) were removed at two commanded flow rates (flow clamps, -7 and -14 ml/sec). Pressure responses to volume removals were analyzed. Although the prototype model accounted for most features of the pressure responses, subtle but systematic discrepancies were observed. The presence or absence of flow and the magnitude of flow affected estimates of model parameters. However, estimates of parameters did not differ when the model was fitted to flow clamps with similar magnitudes of flows but different volume changes. Thus, prototype model inadequacies were attributed to misrepresentations of flow-related effects but not of volume-related effects. Based on these discrepancies, an improved model was built that added to the simple two- state cycling scheme, a pathway to a third state. This path was followed only in response to volume change. The improved model eliminated the deficiencies of the prototype model and was adequate in accounting for all observations. Since the template for the improved model was taken from the cycling crossbridge theory of muscle contraction, it was concluded that, in spite of the complexities of geometry, architecture, and regional heterogeneity of function and structure, crossbridge mechanisms dominated the short-time-scale dynamics of left ventricular chamber behavior.

This article has been cited by other articles:

				K. B. Campbell, A. M. Simpson, S. G. Campbell, H. L. Granzier, and B. K. Slinker Dynamic left ventricular elastance: a model for integrating cardiac muscle contraction into ventricular pressure-volume relationships J Appl Physiol, April 1, 2008; 104(4): 958 - 975. [Abstract] [Full Text] [PDF]

				K. B. Campbell, Y. Wu, A. M. Simpson, R. D. Kirkpatrick, S. G. Shroff, H. L. Granzier, and B. K. Slinker Dynamic myocardial contractile parameters from left ventricular pressure-volume measurements Am J Physiol Heart Circ Physiol, July 1, 2005; 289(1): H114 - H130. [Abstract] [Full Text] [PDF]

				J. Shimizu, K. Todaka, and D. Burkhoff Load dependence of ventricular performance explained by model of calcium-myofilament interactions Am J Physiol Heart Circ Physiol, March 1, 2002; 282(3): H1081 - H1091. [Abstract] [Full Text] [PDF]

				A. Landesberg and S. Sideman Force-velocity relationship and biochemical-to-mechanical energy conversion by the sarcomere Am J Physiol Heart Circ Physiol, April 1, 2000; 278(4): H1274 - H1284. [Abstract] [Full Text] [PDF]

				D. S. Berger, S. K. Fellner, K. A. Robinson, K. Vlasica, I. E. Godoy, and S. G. Shroff Disparate effects of three types of extracellular acidosis on left ventricular function Am J Physiol Heart Circ Physiol, February 1, 1999; 276(2): H582 - H594. [Abstract] [Full Text] [PDF]

				K. B. Campbell, Y. Wu, R. D. Kirkpatrick, and B. K. Slinker Left ventricular pressure response to small-amplitude, sinusoidal volume changes in isolated rabbit heart Am J Physiol Heart Circ Physiol, October 1, 1997; 273(4): H2044 - H2061. [Abstract] [Full Text] [PDF]