Separation of myocardial versus peripheral effects of calcium administration in normocalcemic and hypocalcemic states using pressure-volume (conductance) relationships.

Abstract

This study used left ventricular pressure-volume (conductance) relationships to separate the effects of calcium administration on myocardial performance and peripheral vasoconstriction in normocalcemic and hypocalcemic states. Hypocalcemia was produced in anesthetized dogs with intravenous citrate-phosphate-dextrose until serum [Ca2+] was approximately 0.7 mmol/L. Calcium (CaCl2) bolus (5 mg/kg) was administered during normocalcemia (n = 6) and hypocalcemia (n = 6), and data were collected at 1, 5 and 10 min after CaCl2 administration. During normocalcemia, CaCl2 administration increased [Ca2+] 19% at 1 min and was accompanied by a 47% (P < 0.05) decrease in left ventricular contractility (i.e., end-systolic elastance or E(lves)) and a 13% (P < 0.05) increase in systemic vascular resistance. At 5 and 10 min, serum [Ca2+] and the hemodynamic variables began to return to the baseline values. During hypocalcemia, E(lves) decreased 25% (P < 0.05), but after CaCl2 bolus, it increased to baseline levels and remained there during the 10-min period. Hypocalcemia and the CaCl2 bolus did not significantly affect SVR. In conclusion, these studies suggest that the indications for the use of calcium should depend on the initial serum level of ionized calcium.