Diastolic properties of the canine left ventricle

Abstract

Left ventricular diastolic pressure-volume relations arise from a complex interplay of active decay of force (i.e. relaxation), passive elastic and viscoelastic myocardial properties, and time-varying inflow across the mitral orifice into the chamber that changes its geometry. To investigate each of this components I used a method of LV volume clamping with a remote controlled mitral occluder in five separate canine studies.;The first study was designed to quantify the passive properties of the intact ventricle and the effects of elastic recoil. Eleven open-chest fentanyl-anesthetized dogs were instrumented with aortic and mitral flow probes, LV and LA micromanometers, and a mitral occluder to determine the equilibrium volume (V{dollar}\sb{lcub}\rm o{rcub}{dollar}), i.e., volume at zero transmural pressure and characterize the diastolic passive P-V relation.;This approach was used in the second study to evaluate restoring forces in the hypertrophied left ventricles of six dogs. In hypertrophied ventricles the elastic recoil mechanism which normally facilitates early filling is unlikely to exist, and may be a component in the impairment of filling frequently seen in hypertrophy.;The third study was designed to uncouple passive forces from deactivation in order to reveal the instantaneous rate and duration of myocardial relaxation. I found that myocardial relaxation is modulated by filling which slows its rate and increases its duration, and is therefore a function of both ventricular volume and time.;In the fourth study I used the method of ventricular volume clamping to compare the pressure at a given volume of the fully relaxed ventricle at zero strain rate with the pressure at the same volume and high strain rate. In six open-chest fentanyl-anesthetized dogs I showed that viscoelastic effects are insignificant for the study of one-beat diastolic mechanics.;The fifth study was designed to investigate the relationship between left ventricular geometry and the passive elastic LV properties in eight open-chest dogs. I found that the shape changes are related to the elastic forces in the ventricle and the presence of restoring forces in a small ventricle facilitates filling by decreasing the energy losses across the mitral valve.