A Fundamental Similarity Between Isolated Muscle Mechanics and Cardiac Chamber Dynamics

Abstract

The fundamental similarity that I want to discuss here is that which becomes evident when one compares the pressure-volume relation in the ventricular chamber against the force-length relation of isolated heart muscle. Perhaps no one will doubt that there is a close correspondence between ventricular pressure P(t) and myocardial force F(t) and an even closer interrelation between ventricular lumen V(t) and muscle length L(t). At the same time, no one will doubt that an accurate translation of ventricular P-V variables into muscle F-L variables is a formidable task for many reasons such as the complex shape and non-uniform thickness of the ventricular wall, the complex fibre course, and complex patterns of propagation of excitation and relaxation waves. The inverse path, that is, from one-dimensional muscle mechanics to the three-dimensional world has been fairly well beaten by modellers who assumed simple geometry, homogeneous wall, isotropic material property. Even this conceptual path is considerably bumpy to most cardiologists. Under the circumstances it is justifiable and it may even be wise to pursue entirely separate models, one for ventricular contraction and another for myocardial contraction. Nevertheless, a number of able researchers have challenged various aspects of the difficult task of unifying the two and some of them are presenting here the able consequences of their attempts. In the following I will review examples of parallelism between ventricular pressure-volume relationship and myocardial force-length relationship.