Left ventricular stiffness during diastole and systole: The influence of changes in volume and inotropic state

AUTHORS' SYNOPSIS: A new technique has been developed to investigate in vivo the mechanical properties of the left ventricle during both diastole and systole. A flow-pulse generator was used to induce sinusoidal volume changes of constant amplitude into an isovolumically contracting left ventricle at a frequency several times greater than that of the heart. The resulting peak-to-peak pressure changes were used to determine volume stiffness or elastance, the ratio of the change in pressure to the change in volume. Determination of volume stiffness was made possible by subtraction of an averaged unperturbed pressure cycle from a comparable perturbed cycle obtained during use of the flow-pulse generator. The individual effects on volume stiffness of changes in ventricular volume, heart rate, and noradrenaline were studied. For these interventions, a single linear relationship between volume stiffness and ventricular pressure was established for any given dog. An increase in ventricular volume and in heart rate and the administration of noradrenaline resulted in higher values of peak systolic pressure and volume stiffness. Diastolic increases in pressure and stiffness were elicited by larger ventricular volumes and by certain higher heart rates.