Cardiac Output in Various Plasma Calcium Ion Concentration in Rabbit

Cardiac output was measured in rabbit under various plasma calcium ion concentrations induced by the intravenous infusion of EDTA or calcium chloride solution. Cardiac output 、，v a s determined by means of saline dilution method, recording on physiograph the extra-arterial conductivity, and analysed using Stewart-Hamilton formula. 1. Nonnal cardiac output measured by saline cond• uctivity method in rabbit was 88(±5.4) ml/min in 1. 9-2. 0 kg body weight. Stroke volume, heart rate , mean arterial blood pressure and total perip• heral resistance were O. 36(±0. 03) ml, 256(±4.2) Imin, 102(±2.0) mmHg and 1. 40(±0.1l)mmHg' min/mI , respectively. 2. Decreasing the plasma calcium ion concentration to 0.5, 1, 2. 3 mEq/L, cardiac output revealed to decrease to 84, 48, 48 and 41 per cent of nor mal , respectively. Decrement of cardiac ouput were consistant and significant when calcium ion level decreased more than 1 mEq/L. 3. Increasing, on the other hand, the plasma calcium lOn concentration to 0.5, 1. 2. 3 mEq/L, no siguificant change of cardiac output was recozniged. However, there was a tendency to decrease when calcium level elevated more than 3 mE/L. 4. Considering the similar pattern of change between the cardiac output and stroke volume, the derease of cardiac output in hypocalcemia was attributed primarily to the decreased stroke volume. 5. During the experimental hypocalcemia and tetany, in spite of abrupt decrement of cardiae output, arterial blood pressure was moderately well regulated and maintained. The mechanism of inotropic and chronotropic effects of calcium ion was discussed