Relation of V _max to Different Models of Cardiac Muscle

Abstract

The present study was undertaken to reevaluate the effects of preload on maximum velocity of shortening at zero load, V max , relative to the lengthtension curve. Force-velocity relations were measured from afterloaded isotonic contractions and were calculated from isometric contractions of isolated cat papillary muscles. Results were interpreted in the light of three alternative mechanical models of muscle. V max was obtained by mathematical extrapolation of each force-velocity relation to zero load using a hyperbolic least-squares analysis performed on an IBM 360 computer. With the application of all three muscle models to isotonic force-velocity relations, V max was relatively constant at low preloads but was reduced substantially as muscle length approached L max (the length at the peak of the active length-tension curve). In force-velocity relations from isometric contractions, similar results were obtained with the two-element and Voigt models of muscle. With the Maxwell model, V max remained more nearly constant near L max . Peak developed force (isometric contraction), maximum dP/dt, peak calculated velocity of the contractile element (V CE ), and V max were compared in terms of their dependence on preload and length over the entire length-tension curve (using the Maxwell model). Peak V CE and V malc were similar and were less dependent on preload than maximum dP/dt or developed force. KEY WORDScontractile element series elastic element parallel elastic element Frank-Starling mechanism Voigt model Maxwell model cat papillary muscle preload contractile state• The classic studies of A. V. Hill (1) identified the hyperbolic relation between the velocity of shortening and force development as the most fundamental mechanical relation of skeletal muscle. The extension of this forcevelocity relation to cardiac muscle (2, 3) provided a precise means for quantifying the mechanical behavior of the myocardium. In particular, the extrapolated maximum velocityFrom the

The Influence of Preload Measured as Diastolic Mural Force on Myocardial Contractility Indices

“…However, this concept has become subject to criticism since it is usually determined by the use of total pressure (Voigt model for cardiac muscle) and thus dependent upon preload (12,13). Results from this study support the claim of preload dependence, with Vpm decreasing as preload increases.…”

“…The index (dP/dt)/CPIP, or as in this study (dP/dt)K. 30, has been considered to be the most reliable index for measuring contractility (2,12) ; therefore, the effects of an increased preload due to increasing blood volume were examined in all dogs using LVEDP as an index of preload as well as ADMF in the 12 dogs in which this was determined. The results of this examination are summarized in Table 11.…”

Load Independence of the Instantaneous Pressure-Volume Ratio of the Canine Left Ventricle and Effects of Epinephrine and Heart Rate on the Ratio

“…The computed ratio curve was recorded on an ink-pen recorder (Brush Mark 260) at a speed of 125 mm/sec simultaneously with pressure and volume curves reproduced from the magnetic tape. As a simultaneous and independent indicator of changes in myocardial contractility, we computed [ (dP/dt)/P]max (13,18), where P is the total ventricular pressure, with an analog computer (Medilab Myoputer).…”

“…Using a geometric model, the ventricular pressure and volume data have been reduced to myocardial fiber force, length, and shortening velocity variables and interpreted in the light of myocardial mechanics (6,8). However, some researchers have recendy questioned the validity of this method (9)(10)(11)(12)(13). Under diese circumstances, studies of the ventricu-From the Department of Biomedical Engineering, School of Medicine, The Johns Hopkins University, Baltimore, Maryland 21205.…”

Passive Elasticity of the Human Left Ventricle

“…[1][2][3] The concept of the parallel elastic element bearing the resting force of the muscle in the Maxwell model was applied to the intact heart and the diastolic behavior was assumed to represent the analog parallel elastic element. Analysis of the diastolic resting force is able to differentiate elevated filling pressure of myocardial failure from muscle stiffness.…”