SEPARATION OF MYOCARDIAL VERSUS PERIPHERAL EFFECTS OF CALCIUM ADMINISTRATION IN NORMOCALCEMIC AND HYPOCALCEMIC STATES USING PRESSURE-VOLUME(CONDUCTANCE) RELATIONSHIPS

This study used left ventricular pressure-volume (conductance) relatio nships to separate the effects of calcium administration on myocardial performance and peripheral vasoconstriction in normocalcemic and hypo calcemic states. Hypocalcemia was produced in anesthetized dogs with i ntravenous citrate-phosphate-dextrose until serum Ca2+! was almost-eq ual-to 0.7 mmol/L. Calcium (CaCl2) bolus (5 mg/kg) was administered du ring normocakemia (n = 6) and hypocalcemia (n = 6), and data were coll ected at 1, 5 and 10 min after CaCl2 administration. During normocalce mia, CaCl2 administration increased Ca2+! 19% at 1 min and was accomp anied by a 47% (P < 0.05) decrease in left ventricular contractility ( i.e., end-systolic elastance or E1ves) and a 13% (P < 0.05) increase i n systemic vascular resistance. At 5 and 10 min, serum Ca2+! and the hemodynamic variables began to return to the baseline values. During h ypocalcemia, E1ves decreased 25% (P < 0.05), but after CaCl2 bolus, it increased to baseline levels and remained there during the 10-min per iod. Hypocalcemia and the CaCl2 bolus did not significantly affect SVR . In conclusion, these studies suggest that the indications for the us e of calcium should depend on the initial serum level of ionized calci um.