[Effects of calcium on left ventricular diastolic function in anesthetized dogs]

The effects of extracellular calcium concentration on isovolumic relaxation, rapid filling phase, and passive properties of left ventricle, were studied in open chest dogs instrumented with ultrasonic crystals, and a miniature pressure transducer. A single dose of calcium chloride (0.025 mEq/kg/m) was administered to each dog. In another experimental group beta-adrenergic blockade (propranolol 2 mg/kg) was induced before calcium administration. Diastolic function was evaluated using the time constant of the isovolumic relaxation (tau), the ratios between both +dP/dtmax and -dP/dtmax, and +dP/dt and -dP/dT at the common pressure of 35 mmHg, +dD/dtmax (as an equivalent of peak filling rate) and the chamber stiffness constant (Kc). To avoid the problem that rapid filling phase includes a portion of isovolumic relaxation, the concept of passive pressure for calculation of Kc was used. Calcium produced more increase in +dP/dtmax than in -dP/dtmax. The ratio between both maximal velocities was increased. When both velocities were examined at the common pressure of 35 mmHg, the ratio between them was not changed. tau was not changed but the asymptotic value was decreased. +dD/dtmax was increased, and Kc did not change. The same results on diastolic function of left ventricle were obtained after beta-adrenergic blockade. These data suggest that increased extracellular calcium did not alter the relaxation rate and chamber stiffness, but increased the peak filling rate and decreased the value towards left ventricular pressure decays.