Relation between ionized calcium concentration and ventricular pump performance in the dog under hemodynamically...

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Calcium Homeostasis

Background:

• Left ventricular function is crucial for systemic circulation.
• Plasma ionized calcium levels play a vital role in myocardial contractility.
• Understanding calcium's effects is key to managing cardiac conditions.

Purpose of the Study:

• To investigate the direct effects of varying plasma ionized calcium concentrations on canine left ventricular function.
• To quantify the impact of hypercalcemia and hypocalcemia on cardiac performance metrics.
• To establish the relationship between ionized calcium levels and left ventricular end-diastolic pressure and stroke work.

Main Methods:

• Utilized a canine right heart bypass model with controlled stroke volume, mean arterial pressure, and heart rate.
• Administered citrate to induce hypocalcemia (0.58 mM) and calcium chloride to induce hypercalcemia (1.70 mM).
• Compared left ventricular function parameters (dP/dt, end-diastolic pressure, stroke work) against a normocalcemic baseline.

Main Results:

• Sustained hypercalcemia showed a small decrease in left ventricular end-diastolic pressure and a 34% increase in peak left ventricular dP/dt.
• Hypocalcemia caused a marked depression in left ventricular function, increasing end-diastolic pressure significantly and reducing stroke work by 52%.
• Hypercalcemia slightly improved stroke work (11%), while hypocalcemia severely impaired it, demonstrating a clear dose-dependent effect of calcium.

Conclusions:

• Hypercalcemia provides only a modest enhancement of ventricular pump performance from a normal baseline.
• Marked improvement in left ventricular function is observed when calcium infusion follows a period of hypocalcemia.
• Plasma ionized calcium concentration is a critical determinant of left ventricular performance, with hypocalcemia posing a significant risk.