Elastic and viscous stiffness of the canine left ventricle.

viscous stifness of the canine left ventricle. J. Ap pl. Ph ysiol. 36 ( I): 123-I 27. 1974.-Elastic and viscous stiffness of canine left ventricles was measured continuously over the entire cardiac cycle. These mechanical properties were determined from the sinus-oidally varying portion of the left ventricular pressure induced by an externally applied sinusoidal volume change with a constant peak amplitude of 0.5 ml and a frequency of 22 Hz. The sinusoidal pressure perturbations varied during the cardiac cycle both in peak amplitude and in the time of occurrence of the peak ampli-tude with respect to the volume changes that produced them. De-terminations were made of ventricular stiffness, or elastance, which is defined as the ratio of the peak change in the pressure perturbations to the peak change in volume. Stiffness and the time difference between the occurrence of the peak volumetric perturbation and the corresponding peak of the pressure perturba-