Abstract 4732: Determinants of Left Ventricular Early Diastolic Lengthening Velocities
The proposed determinants of the LV wall early diastolic lengthening velocity (E′) are: relaxation rate of active fiber stress (tau), LV pressure during early filling, restoring forces, and passive elastic wall stiffness. In experimental and clinical studies the individual determinants are difficult to alter and investigate separately due to their inter-dependency. The purpose of this study was to develop a mathematical model that provided a physical basis for the determinants and to validate their individual effect on E′. The LV wall was represented by a lumped parameter model consisting of two elements in parallel (Fig. a⇓): one representing the active fiber stress (Sa) and the other the passive elastic stress (Sp) represented by an elastic spring with stiffness K and resting length L0. The sum of active and passive wall stresses was set to equal LV pressure (LVP). Active stress was prescribed to decay exponentially. E′ was assessed during a simulation with baseline model parameter values and a higher value of each parameter in turn. At baseline E′ was 6.2 cm/s. E′ was decreased to 4.1 cm/s and delayed by prolonging relaxation from tau = 40 to 60 ms (Fig. b⇓). Increasing LVP during early filling by 5 mmHg increased E′ to 10.6 cm/s (Fig. c⇓). Decreasing restoring forces by increasing end systolic length from 57 to 60 mm decreased E′ to 2.6 cm/s (Fig. d⇓). Increasing passive stiffness from K=1500 to 3000 mmHg/m decreased E′ to 5.1 cm/s (Fig. e⇓). The mathematical model validated former experimental results and confirmed that E′ increases with shortening of tau, increase of diastolic LVP, decreased end systolic length, and decreased passive stiffness.