We evaluated the effect of milrinone (MIL) on venous return by constructing the right ventricular output curve and systemic venous return curve.
In the open-chest dogs (n=12) anesthetized with intravenous pentobarbital, total spinal anesthesia was performed to eliminate the baroreflex. The dogs were divided into two groups, i.e. Non-MIL group (n=6) and MIL group (n=6) receiving an intravenous MIL (100μg/kg + 2.5,μg/kg/min ). We measured the mean circulatory pressure (MCP) and other hemodynamic parameters at the baseline (before blood volume change), immediately after blood letting (5ml/kg) and immediately after dextran injection (5ml/kg). Taking the right atrial pressure (RAP) on the abscissa and the cardiac output (CO) on the ordinate, we drew the right ventricular output curve. The systemic venous return curve was drawn by connecting the CO-RAP plot to the point of MCP on the abscissa. The slope of the systemic venous return curve represents the resistance to venous return (RVR).
MIL shifted the right ventricular output curve to the left and upwards, and shifted the systemic venous return curve to the left (MCP being decreased) and rotated it clockwise (RVR being decreased). These results suggest that venous return was increased by decreasing RVR and by increasing the right ventricular pump function.
