Influence of aging on left ventricular hemodynamics and stiffness in beagles.

We studied the influence of aging on the contractile performance, stiffness, and contraction time of the canine left ventricle. Eight young (27 +/- 2.5 months, mean +/- SE) and seven old (128 +/- 20.5 months) beagles were placed on complete cardiopulmonary bypass, the arterial pressure was adjusted to 80 mm Hg, and the heart contracted isovolumically at a paced rate of 120 beats/min. Diastolic pressure-volume curves were established for each unpaced left ventricle at the beginning of each experiment, and the volume at the knee of the curve was used during the subsequent data collection when the heart was paced. Stiffness was measured with a sinusoidal forcing function, which imposed a sinusoidal displacement of 1 ml at 20 Hz into a balloon placed in the left ventricle. In each ventricle, stiffness was related linearly to pressure during the cardiac cycle, and was greater for any given pressure in the older beagles. Contraction duration was prolonged in the older dogs. In an additional seven old beagles during right heart bypass time, and duration of contraction were longer than in seven young beagles. Aging of the beagle heart is associated with an increase in left ventricular systolic and diastolic stiffness and prolonged duration of contraction.