Contractile Filament Stress: Comparison of Different Disease States in Man

Cardiac catheterization data on 39 patients was classified in 5 cardiovascular groups: normal, compensated volume overload, decompensated volume overload, compensated pressure overload, and congestive cardiomyopathy. Both the Lagrangian stress and contractile filament stress for the circumferential axis and the longitudinal axis were computed over a complete cardiac cycle. Contractile filament stress was 24% higher than Lagrangian stress in the circumferential direction, and 43% higher than Lagrangian stress in the longitudinal direction. The percent difference in stress between the contractile filament stress and Lagrangian stress was greatest for patients with pressure overload, and least for patients with compensated volume overload. No significant difference in calculated wall stress was noted between the normal group and the 4 pathological groups. Circumferential velocity of the contractile element occurring at peak stress was plotted as a function of peak contractile filament stress and patients with compensated pressure overload exhibited high values of both velocity and peak stress. Patients with congestive cardiomyopathy showed low values of both velocity and peak stress. Circumferential velocity of the contractile element occurring throughout the cardiac cycle was plotted as a function of both the instantaneous Lagrangian stress and the instantaneous contractile filament stress, resulting in 2 stress-velocity curves for each patient. The value of the maximum velocity extrapolated from either stress-velocity curve was approximately the same, but the maximum stress extrapolated from the contractile filament stress-velocity curve was significantly higher than the maximum stress extrapolated from the Lagrangian stressvelocity curve. The product of peak contractile filament stress in the circumferential direction times heart rate was a clinically useful index of myocardial oxygen consumption, and predicted a lower rate of oxygen consumption than did the product of peak developed stress times heart rate. OHIO J. SCI. 78(5): 259, 1978 Two types of stress have often been employed to describe the mechanics of ventricular contraction: a passive stress, which designates the load placed upon the muscle fibers of the ventricle, and an active stress, which designates the force per unit area developed by the myocardial fibers and transmitted to the ventricular wall. In both cases, stress is dependent upon a knowledge of ventricular pressure, geometry and wall thickness, in addition to some assumptions as to the material properties of the ventricle. Stress is important because it affects the velocity of Manuscript received February 7, 1977 and in revised form June 17, 1977 (#77-15). Present address: Department of Orthopedic Surgery, University of Cincinnati, Cincinnati, OH 44221. muscle fiber contraction and the resultant stress-velocity relationship, which characterizes the heart as an active muscle, and provides a quantitative estimation of cardiac performance. Previous investigators applied stress calculations in a one-dimensional direction, using as a model the isolated muscle fiber which we have previously referred to as the one-dimensional muscle model (Grood et al 1974). Most investigators have only considered passive stress, beginning with Wood (1892) who applied Laplace's Law to the heart. Sandier and Dodge (1963) applied the basic Laplace relation, modified to incorporate wall thickness, to an ellipsoidal left ventricle, but recognized that the application of thin-wall theory to a thick-walled struc-