Left ventricular function and muscle mechanics in hypertrophied rabbit heart

Ventricular contractile performance was studied in relation to wall muscle mechanics in isolated rabbit left ventricles during pressure-overloaded hypertrophy. The isovolumic pressure-volume relation of the hypertrophied ventricle (LVH) shifted to the left and upward from the normal control (NC) (P less than 0.001), but calculated wall stress at each normalized circumferential length decreased in LVH. The pressure-ejection rate relation, determined accurately by velocity control technique, could be adequately approximated by a hyperbola. In LVH, the maximum pressure (Po) was larger (154.3 +/- 17.0 mmHg), whereas the maximum ejection rate (Vej max) was smaller (13.7 +/- 4.2 ml/s, P less than 0.001) than those for NC (127.7 +/- 23.3 mmHg and 22.3 +/- 5.7 ml/s, respectively). The pressure-stiffness relation was linear in both groups, but the vertical axis intercept increased, indicating increased resting stiffness in LVH. Ventricular volume stiffness vs. the mean wall stress relationship of LVH shifted upward, whereas the normalized wall muscle stiffness vs. the mean wall stress relationship of LVH showed a smaller slope. Thus the hypertrophied ventricle can maintain its pumping ability at normal or augmented levels with depressed contractile function of the wall muscle.