Relationships between resting tension and mechanical properties of papillary muscle

Abstract

The influence on mechanical properties of changes in resting tension over a range from 0.5 to 4.5 g was investigated in 12 isolated cat papillary muscles. At each resting tension, the muscles contracted isometrically with the exception of an externally applied sinusoidal stretch of 0.5% Lmax (deltaL) and 20 Hz. Stiffness (deltaT/deltaL) was determined from deltaL and the peak amplitudes (deltaT) of the individual cycles from the sinusoidal component of tension. Assuming that the muscle and experimental apparatus behaved as a linear second-order mechanical system, it was possible to divide stiffness into its elastic and viscous components. During rest, total stiffness and its components were linearly related to tension. During contraction, stiffness and its elastic component were linearly related to tension. Furthermore, increasing resting tension increased the intercept and decreased the slope of this linear stiffness-tension relationship. The relationship between viscous stiffness and tension during contraction is more complex in that it is a direct relationship at low resting tensions, but an inverse one at high resting tensions.

Effects of volatile anesthetics on elastic stiffness in isometrically contracting ferret ventricular myocardium

“…When heart muscle length or load is disturbed sinusoidally, it responds with sinusoidal force or length alterations like a linear second-order mechanical system (24,35,36,38). Inertia, viscosity, and elasticity present in muscle preparations are affected by sinusoidal forcing functions, and measurement of stiffness therefore reflects the response of all three components together.…”

“…This phase shift is quantified by resolving the sinusoid of the received signal into two components, one in phase with the imposed sinusoid and one in quadrature to the imposed sinusoid (i.e., leading or lagging by 90°). We imposed continuous small rapid length perturbations on the muscle attached to the electromagnetic lever system, all of which behaves as a linear second-order mechanical system (24,35,36,38). The relation of the sinusoidal responses to the imposed sinusoidal changes can be described mathematically…”

Diastolic ventricular-vascular stiffness and relaxation relation: elucidation of coupling via pressure phase plane-derived indexes

“…By applying the analog of the kinematic phase plane-derived geometric features of an ideal oscillator's loop in the PPP, we determined new, analogous PPP-derived parameters of stiffness that utilize PPP data and encompass both isovolumic relaxation and filling periods. Furthermore, because P and V can have different phases as a result of viscoelastic effects, stiffness, defined either as dP/dV or E(t) ϭ P(t)/[V(t) Ϫ V o ], relies on the assumption of minimal viscosity (or nearly steady state) change in P and V. However, previous work on viscous and elastic properties of the myocardium (55,56) shows that viscoelastic effects, are in general, not negligible. In diastole, for example, viscoelastic effects during relaxation cause a phase shift between pressure and flow (volume) (58).…”

Analyse viskoelastischer Eigenschaften isolierter Herzmuskelpräparate: Meßmethode und mathematisches Modell (II) - Viscoelastic properties, analysis of isolated heart muscle preparations: Measurement and mathematical model (II)

“…In der Literatur sind bereits Experimente [5,6,32,33,34,35] beschrieben, in denen die zeitabhängigen Eigenschaften von Steifigkeit und Dämpfung während des Kontraktionszyklus untersucht wurden. Dies geschieht durch Überlagerung von Sinuswellen konstanter Dehnungs-Amplitude und verschiedener Frequenzen auf die Muskelzuckung.…”